Paroxysmal Nocturnal Hemoglobinuria

Practice Essentials

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal hematopoietic stem cell (HSC) disease. It is a rare, chronic, debilitating disorder that most frequently presents in early adulthood and usually continues throughout the patient's life. PNH usually presents as hemolytic anemia, thrombosis, and smooth muscle dystonias, as well as bone marrow failure in some cases. PNH results in the death of approximately 50% of affected individuals due to thrombotic complications. Until recently, no specific therapy was available.

PNH is caused by somatic mutations in PIGA (which encodes phosphatidylinositol N-acetylglucosaminyltransferase subunit A) in one or more HSC clones. The gene product of PIGA is required for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors; thus, PIGA mutations lead to a deficiency of GPI-anchored proteins, such as complement decay-accelerating factor (also known as CD55) and CD59 glycoprotein (CD59), which are both complement inhibitors.

Clinical manifestations of PNH occur when a HSC clone carrying somatic PIGA mutations acquires a growth advantage and differentiates, generating mature blood cells that are deficient of GPI-anchored proteins. The loss of CD55 and CD59 renders PNH erythrocytes susceptible to intravascular hemolysis, which can lead to thrombosis and to much of the morbidity and mortality of PNH. The accumulation of anaphylatoxins (such as C5a) from complement activation might also have a role.

The name of the disorder is a descriptive term for the clinical consequence of red blood cell (RBC) breakdown with release of hemoglobin into the urine, which manifests most prominently as dark-colored urine in the morning (see image below).

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This series of containers holds urine of a patient with paroxysmal nocturnal hemoglobinuria, showing the episodic nature of the dark urine (hemoglobin....

The term "nocturnal" refers to the belief that hemolysis is triggered by acidosis during sleep and activates complement to hemolyze an unprotected and abnormal RBC membrane. However, this supposition was later disproved. Hemolysis has been shown to occur throughout the day and is not actually paroxysmal, but the concentration of urine overnight produces the dramatic change in color.

PNH has been referred to as "the great impersonator" because of the variety of signs and symptoms observed during its initial manifestation and course. This variety reflects the contributions of the following three underlying pathophysiologic events^{[1, 2, 3, 4, 5]} :

• An acquired intracorpuscular hemolytic anemia due to the abnormal susceptibility of the RBC membrane to the hemolytic activity of complement
• Thromboses in large vessels, such as hepatic, abdominal, cerebral, and subdermal veins
• A deficiency in hematopoiesis that may be mild or severe, such as pancytopenia in an aplastic anemia state

The triad of hemolytic anemia, pancytopenia, and thrombosis makes PNH a unique clinical syndrome.

The principal studies used to establish the diagnosis of PNH are flow cytometry of peripheral blood and bone marrow analysis. Flow cytometry measures the percentage of cells with the deficiency in complement-regulating surface proteins that underlies PNH; bone marrow analysis differentiates classic PNH from PNH secondary to other bone marrow disorders. (See Workup).

Several complement inhibitors (eg, pegcetacoplan, eculizumab, ravulizumab, crovalimab, iptacopan, danicopan) are approved for treatment of PNH. These drugs target varioius complement factors, resulting in reduction of the hemolysis associated with PNH and its sequelae. The complement inhibitors can dramatically alleviate symptoms, improve quality of life, and eliminate complications of PNH; however, they do not alter the underlying defect of the disease. Allogeneic hematopoietic stem cell transplantation is curative but it requires a histocompatible donor and is associated with significant morbidity and mortality, so it is reserved for severe cases of PNH with aplastic anemia or transformation to leukemia. See Treatment.

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Pathophysiology

Paroxysmal nocturnal hemoglobinuria (PNH) was previously classified as purely an acquired hemolytic anemia due to a hematopoietic stem cell mutation defect. This classification was abandoned because of the observation that surface proteins were missing not only in the RBC membrane but also in all blood cells, including the platelets and white cells.

The common denominator in the disease, a biochemical defect, appears to be a genetic mutation leading to the inability to synthesize the glycosyl-phosphatidylinositol (GPI) anchor that binds these proteins to cell membranes.^{[5, 6, 7]} The corresponding gene PIGA (phosphatidylinositol glycan class A) in the X chromosome can have several mutations, from deletions to point mutations.^[8]

Due to its location on the X chromosome, and X inactivation in female somatic cells, only one mutation is required in either males or females to abolish the expression of GPI-linked proteins. Most type II PNH cells (total lack of GPI-linked protein) are due to a frame shift mutation occurring in the early hematopoietic progenitor cells, resulting in the same mutation in all blood cell lines.

The essential group of membrane proteins that are lacking in all hematopoietic cells in PNH are called complement-regulating surface proteins, including the decay-accelerating factor (DAF), or CD55^[9] ; homologous restriction factor (HRF), or C8 binding protein; and membrane inhibitor of reactive lysis (MIRL), or CD59.^[10] All of these proteins interact with complement proteins, particularly C3b and C4b, dissociate the convertase complexes of the classic and alternative pathways, and halt the amplification of the activation process.

The absence of these regulating proteins results in uncontrolled amplification of the complement system. This leads to intravascular destruction of the RBC membrane, to varying degrees. See the image below.

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In paroxysmal nocturnal hemoglobinuria (PNH), the absence of anchor proteins that bind complement-regulating proteins (eg, CD55, CD59) to the surface ....

Breakdown of RBC membranes by complement leads to the release of hemoglobin into the circulation. Hemoglobin is bound to haptoglobin for efficient clearance from the circulation. After saturating the haptoglobin, free hemoglobin circulates and binds irreversibly with nitric oxide (NO), depleting NO levels in peripheral blood.

Because NO regulates smooth muscle tone, depletion of NO levels leads to smooth muscle contraction, with consequent vasoconstriction, constriction of the gut, and pulmonary hypertension. Resultant symptoms may include the following:

• Abdominal pain
• Bloating
• Back pain
• Headaches
• Esophageal spasms
• Erectile dysfunction
• Fatigue

Progressive chronic kidney disease can occur after several years of hemoglobinuria from the acute tubulonecrosis effects of heme and iron (pigment nephropathy), decreased renal perfusion from renal vein thrombosis, and tubular obstruction with pigment casts. Patients with PNH experience a high incidence (40%) of thrombotic events (mostly venous) in large vessels (cerebral, hepatic, portal, mesenteric, splenic, and renal veins) and, most recently recognized, arterial thrombosis.

The pathophysiology of thrombophilia in PNH is not fully understood, but the increased incidence during hemolytic episodes suggest a direct relationship with the hemolytic process. Increased procoagulant and fibrinolytic activity, suggesting increased fibrin generation and turnover, increased plasma levels of urokinase-type plasminogen activator, and platelets deficient in GPI-linked proteins activated by complement, have been implicated. However, none of these identified platelet and coagulation abnormalities can fully explain the hypercoagulable state in PNH.

Bone marrow failure is defined as peripheral cytopenias associated with decreased hematopoiesis. Bone marrow dysfunction is present in all patients with PNH, even when peripheral blood counts are normal and the bone marrow is hypercellular. The degree of marrow failure may vary from severe aplastic anemia to a decrease in the number of hematopoietic stem cells. Bone marrow failure is possibly due to similar destruction by complement, but the cause or causes are still poorly understood.

Venous thrombosis usually manifests as a sudden catastrophic complication, with severe abdominal pain, a rapidly enlarging liver, and ascites (Budd-Chiari syndrome). This thrombosis may be due to a lack of CD59 on platelet membranes, which induces platelet aggregation and is highly thrombogenic, particularly in the venous system.

Deficient hematopoiesis may occur due to diminished blood cell production by a hypoplastic bone marrow; thus, patients have a 10-20% chance of developing aplastic anemia in their course. In turn, PNH eventually develops in 5% of patients with aplastic anemia.^{[8, 11]} The nature of the pathogenetic link between those two diseases is still unknown.

Pathogenesis

When intravascular hemolysis occurs, RBCs release hemoglobin (Hb) into the plasma. This free Hb is rapidly dimerized and bound by serum protein haptoglobin and rapidly removed by macrophages, which then degrades it after endocytosis. Since haptoglobin is not recycled, large amounts of free Hb can deplete the body's supply, leaving the excess Hb free in the plasma.

When the capacity to manage and degrade free Hb during acute or chronic hemolysis is reached, levels of Hb and heme increase in the plasma and urine. Plasma Hb has the ability to scavenge nitric oxide (NO), resulting in rapid consumption of NO and clinical sequelae of NO depletion. NO plays a major role in vascular homeostasis and has been shown to be a critical regulator of basal and stress-mediated smooth muscle relaxation and vasomotor tone, endothelial adhesion, and platelet activation and aggregation.

Thus, the clinical consequences of excessive cell-free plasma Hb levels during intravascular hemolysis or the administration of Hb preparations include dystonias involving the gastrointestinal, cardiovascular, pulmonary, and urogenital systems, as well as clotting disorders. Many of the clinical sequelae of intravascular hemolysis in a prototypic hemolytic disease, PNH, are readily explained by Hb-mediated NO scavenging.

Paroxysms or episodes of symptoms occur during sudden and marked increases in the rate of intravascular hemolysis. These episodes can be precipitated by infections, drugs, or trauma or they can occur spontaneously. During paroxysms, PNH patients exhibit symptoms consistent with smooth muscle perturbation through the release of Hb and NO scavenging, including abdominal pain, esophageal spasms, and erectile dysfunction.

NO also plays an important role in the maintenance of normal platelet functions through the down-regulation of platelet aggregation and adhesion and the regulation of molecules in the coagulation cascade. Accordingly, the long-term consumption of NO by plasma Hb has been implicated in the formation of clots in PNH patients.^[12]

Thrombosis is the most common cause of death in persons with PNH, accounting for 50% of the mortality from the disease. The most frequent sites of thrombosis include the hepatic, pulmonary, cerebral, and deep and superficial veins, as well as the inferior vena cava. Approximately 15%-20% of thrombosis in PNH is arterial.^[13] Interestingly, there is a close correlation between thrombosis and a large PNH clone, and clone size correlates with hemolytic rates.

The reason for the propensity for thrombosis is not entirely clear. Intravascular hemolysis may provide altered membrane surfaces upon which coagulation may be initiated.

More likely, it is the effect of the activation of complement on platelets and perhaps endothelial cells. In platelets, the deposition of C9 complexes on the surface stimulates their removal by vesiculation; these vesicles are very thrombogenic. Because PNH platelets lack the mechanism for down-regulating C9 deposition (ie, CD59), even a minimal stimulus from activated complement results in a greatly increased production of these vesicles.^[14]

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Etiology

For some time, paroxysmal nocturnal hemoglobinuria (PNH) has been known to result from somatic mutations in the PIGA gene, which encodes phosphatidylinositol glycan class A (PIGA). These mutations result in hematopoietic stem cells that are deficient in glycosyl-phosphatidylinositol anchor protein (GPI-AP). Nonmalignant clonal expansion of one or several of these stem cells leads to clinical PNH.

Shen et al have identified additional somatic mutations associated with PNH. These mutations are in genes known to be involved in myeloid neoplasm pathogenesis, including TET2, SUZ12, U2AF1, and JAK2. Clonal analysis indicated that these additional mutations arose either as a subclone within the PIGA-mutant population or had occurred prior to PIGA mutation.^[15]

The clinical pathology in PNH may actually be an epiphenomenon resulting from an adaptive response to injury, such as an immune attack on hematopoietic stem cells.

In PNH, the peripheral blood and bone marrow is a mosaic composed of GPI-AP+ and GPI-AP– cells; with GPI-AP–, cells can be derived from multiple mutant stem cells. The GPI-AP–mutant cells may appear to dominate hematopoiesis in PNH by providing a proliferative advantage under some pathologic conditions. For example, if damage to stem cells causing bone marrow failure is mediated through a GPI-linked surface molecule, the PNH cells lacking these molecules will survive. The close association of PNH with aplastic anemia and myelodysplastic syndrome (MDS) suggests that the selection process arises as a consequence of this specific type of bone marrow injury.

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Epidemiology

Paroxysmal nocturnal hemoglobinuria (PNH) incidence is estimated at 1–1.5 cases per million individuals worldwide, but might be higher in certain regions. The disease occurs more frequently in countries in Asia (for example, Japan, Korea and China) than in western countries (the United States, Spain and the United Kingdom). 

The rarity of PNH has prompted the establishment of registries for collecting information about the disease. The International PNH Registry was established in 2003 to collect comprehensive data on the natural history of PNH and can provide some epidemiology data.^{[16, 17]}  Patients of any age with a clinical diagnosis of PNH (by any applicable diagnostic method) or a detectable fraction of PNH-affected blood cells (that is, a PNH clone) of ≥0.01% of all blood cells are eligible for inclusion.

As of June 30, 2012, 1610 patients from 273 centers in 25 countries were enrolled; of these patients, 92.5% were from Europe and North America and 87.5% were of White ethnicity. No definitive biological data exist to fully explain this distribution; furthermore, there may be bias in the registry. The remaining patients were of Asian or Pacific Island descent (5%), African descent (3.5%), native/Aboriginal descent (0.2%), or of other or unknown ethnicity (3.9%).

A limitation of the data from the International PNH Registry is that information on PNH is not available from all countries. Furthermore, many patients enrolled in the International PNH Registry have aplastic anemia as their primary diagnosis, as the registry allows inclusion of patients with > 0.01% PNH granulocytes. Thus, these prevalence rates are not only based on patients with hemolytic PNH.

The Global PNH Registry, initiated in 2021, is a patient-driven and patient-focused PNH registry. It is open to individuals with a self-reported PNH diagnosis.^[18]  

Race

Specific clinical manifestations of PNH might vary in different ethnicities. PNH-associated thrombotic events occur in up to 30% of patients in western countries, compared with < 15% of patients in Asian countries. The differences of PNH among races were shown in a study that compared 176 patients from the United States and 209 patients from Japan.^[19] White US patients were younger and had significantly more classic manifestations of the disease, including thrombosis, hemoglobinuria, and infection, whereas Asian patients were older, with more marrow aplasia and a smaller PNH clone. Survival analysis showed a similar death rate in each group, although the causes of death were different, with more thrombotic deaths seen in the US patients. Japanese patients had a longer mean survival time (32.1 vs 19.4 y), but Kaplan-Meier survival curves were not significantly different.^[19]

Other geographic ethnic differences were observed in the thrombosis incidence in 64 patients with classic PNH.^[20] The investigators found that African Americans (n = 11) and Latin Americans (n = 8) had a higher risk or rate of thrombosis by Cox regression analysis and that this had an impact on length of survival compared with other patients (n = 45).^[19]

The epidemiology of PNH-associated bone marrow failure is not as well described in these studies. However, given the overall increased prevalence of aplastic anemia in Asian countries compared with western Europe and the United States, one could hypothesize that PNH-associated bone marrow failure is more common in Asian patients than is thrombosis associated with PNH.^{[21, 22]}

Sex- and age-related demographics

Men and women are affected equally with PNH, and no familial tendencies exist.

PNH may occur at any age, from children (10%) as young as 2 years to adults as old as 83 years, but median age at the time of diagnosis was 42 years (range, 16-75 y) in an English series of 80 consecutive patients.^[23] In childhood through adolescence, patients with PNH presented with more of the primary features of aplastic anemia than the otherwise healthy adult population. Other complications, such as infections and thrombosis, occurred with equal frequency in all age groups.

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Prognosis

The prognosis in patients with paroxysmal nocturnal hemoglobinuria (PNH) is variable, depending on the severity of symptoms and the presence of complications. An aplastic phase is a serious prognostic factor, because the resulting pancytopenia and thrombosis of hepatic, abdominal, and cerebral veins can have life-threatening consequences. Prophylactic anticoagulation has not been shown to be of benefit because of a lack of data from a clinical trial setting.

The disease process of PNH is insidious and has a chronic course, with a median survival of about 10.3 years. Morbidity depends on the variable expressions of hemolysis, bone marrow failure, and thrombophilia that define the severity and clinical course of the disease.

A study of the first 1610 patients enrolled in the International PNH Registry found that overall, 16% of patients had a history of thrombotic events and 14% a history of impaired kidney function. Frequently reported symptoms included the following^[24] :

• Fatigue (80%)
• Dyspnea (64%)
• Hemoglobinuria (62%)
• Abdominal pain (44%)
• Chest pain (33%)

Patients also reported impairment in quality of life from their disease, with 17% stating that they were not working or were working less because of PNH.

In several large studies, the main cause of death in patients with PNH was venous thrombosis, followed by complications of bone marrow failure; however, spontaneous long-term remission or leukemic transformation of the PNH clone has been reported and well documented.

The median survival after diagnosis was 10 years in a series of 80 consecutive patients seen at the Hammersmith Hospital in London who were treated with supportive measures, such as oral anticoagulant therapy after an established thrombosis, and transfusions.^[23]  Sixty patients died; of 48 patients whose cause of death was known, 28 died from venous thrombosis or hemorrhage. Thirty-one individuals (39%) had one or more episodes of venous thrombosis during their illness.^[23]  No leukemic transformations occurred in this series.

Twenty-two of the 80 patients (28%) survived for 25 years.^[23]  Of the 35 patients who survived for 10 years or more, 12 had spontaneous clinical recovery; no PNH-affected cells were found among the RBCs or neutrophils during their prolonged remission, but a few PNH-affected lymphocytes were detectable in 3 of 4 patients tested.^[23]

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History

The classic manifestation of paroxysmal nocturnal hemoglobinuria (PNH) is dark urine during the night with partial clearing during the day (see image below). However, hemoglobinuria may occur every day in severe cases; more frequently, it occurs in episodes lasting 3-10 days; and in some cases, it does not occur at all.

View Image

This series of containers holds urine of a patient with paroxysmal nocturnal hemoglobinuria, showing the episodic nature of the dark urine (hemoglobin....

A working classification has been developed for PNH that includes all the variations in its presentation, clinical manifestations, and natural history. PNH can present as any of the following three syndromes or sets of symptoms:

• Classic PNH
• PNH in the setting of another specified bone marrow disorder (eg, PNH/aplastic anemia or PNH/refractory anemia–myelodysplastic syndrome [MDS])
• Subclinical PNH (PNH-sc)

Hemolytic anemia is usually in the form of intravascular hemolysis. The most common presentation is the presence of anemia associated with dark cola-colored urine that is a manifestation of hemoglobinuria. The latter may be confused with hematuria, and erroneous treatment could be given for urosepsis.

Thrombosis involves the venous system, and it typically occurs in unusual veins, namely the hepatic, abdominal, cerebral, and subdermal veins. The tendency of patients with PNH to suffer thrombosis has been recognized as a major part of the syndrome and interpreted as a very bad prognostic sign and the most common cause of death in PNH. About 30-40% of patients of European origin have serious thrombosis at some time; for unexplained reasons, only 5-10% of patients of East Asian (Chinese, Japanese, and Thai) or Mexican origin develop this complication.^{[25, 26]}

Hepatic vein thrombosis results in Budd-Chiari syndrome, which manifests as a sudden and catastrophic event characterized by jaundice, abdominal pain, a rapidly enlarging liver, and accumulation of ascitic fluid. This syndrome may be severe and lead to vascular collapse and death, or it can be slow and insidious, leading to liver failure.

Abdominal vein thrombosis presents as upper abdominal pain, or pain elsewhere in the abdomen, lasting 1-6 days. It can lead to bowel infarction in severe cases.

Cerebral vein thrombosis can range from the mildest form to a severe headache, depending on which veins are involved. The sagittal vein is commonly affected, which can give rise to papilledema and pseudotumor cerebri.

Dermal vein thrombosis manifests as raised, painful, red nodules in the skin affecting large areas, such as the entire back, which subsides within a few weeks, usually without necrosis. In cases that do result in necrosis, skin grafting may be necessary.

Patients with deficient hematopoiesis usually present with anemia, despite the presence of an erythroid marrow with suboptimal reticulocytosis. In some cases, neutropenia and thrombocytopenia can occur in a hypoplastic bone marrow similar to aplastic anemia (aplastic episodes).

Other symptoms of PNH include esophageal spasms that occur in the morning and, like the dark-colored urine, clear up later in the day. In males, erectile dysfunction can occur concomitantly with hemoglobinuria; the cause of this is unknown.

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Physical Examination

Most commonly, in patients with paroxysmal nocturnal hemoglobinuria (PNH), pallor suggests anemia; fever suggests infections; and bleeding, such as mucosal bleeding or skin ecchymoses, suggests thrombocytopenia similar to that in aplastic anemia. Other physical examination findings may include the following:

• Hepatomegaly and ascites in the presence of Budd-Chiari syndrome
• Splenomegaly in the presence of splenic vein thrombosis
• Absent bowel sounds in the presence of bowel necrosis
• Papilledema in the presence of cerebral vein thrombosis
• Skin nodules that are red and painful in the presence of dermal vein thrombosis

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Approach Considerations

In addition to a complete blood cell count, the principal studies used to establish the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) are flow cytometry of peripheral blood and bone marrow analysis. Flow cytometry measures the percentage of cells that are deficient in the glycosyl phosphatidylinositol–anchored proteins (GPI-APs) and identifies discrete cell populations with different degrees of deficiency. Because of the missing GPI-APs, red blood cells (RBCs) and other cells in patients with PNH lack complement decay-accelerating factor (CD50) and membrane inhibitor of reactive lysis (CD59), which regulate complement.

Hemosiderin is nearly always present in the urine sediment and can accumulate in the kidneys; this is visible on magnetic resonance images (MRI) or computed tomography (CT) scans. An elevated reticulocyte count and serum lactate dehydrogenase (LDH) level with a low serum haptoglobin level in the absence of hepatosplenomegaly are the hallmarks of intravascular hemolysis.

Bone marrow examination will differentiate classic PNH from PNH that develops in the setting of other bone marrow disorders.^[29] In addition, bone marrow examination will identify an erythroid and hyperplastic bone marrow during the hemolytic phase or a hypoplastic bone marrow in the aplastic phase.

Imaging studies are indicated in patients with venous thrombosis.

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Laboratory Studies

The tests involved in establishing the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) demonstrate the presence of red blood cells (RBCs) that are exceptionally sensitive to the hemolytic action of complement. These tests include the following:

• Flow cytometry
• Acidified serum lysis and Ham test
• Complement lysis sensitivity test
• Sugar water or sucrose lysis test

Most laboratories no longer perform the Ham test or the sugar water test.

Flow cytometry

The state-of-the-art laboratory test is flow cytometry of the patient's blood to detect complement decay-accelerating factor (CD50) and membrane inhibitor of reactive lysis (CD59), which are invokved in regulation of complement action. Absence or reduced expression of both CD59 and CD55 on RBCs is diagnostic of PNH.

The use of flow cytometry in PNH differs from many applications in that the diagnosis depends upon demonstrating the absence of relevant antigens. In this context, it is important that at least two glycosyl-phosphatidylinositol (GPI)–linked antigens are studied to exclude rare congenital deficiencies of single antigens (CD55 and CD59) and polymorphism with individual antigens (CD16), which render them undetectable by some monoclonal antibody clones.

Standard and high-sensitivity flow cytometric procedures for detecting PNH cells are now available.^[30] For routine analysis and diagnosis of suspected PNH, the standard test is sufficient. This test can detect 1% or more PNH cells, but most laboratories report only 10% or more as a positive result. High-sensitivity analysis (in which as little as 0.01% PNH cells can be detected) may be helpful in aplastic anemia patients, who may eventually develop PNH, and possibly in those with hypoplastic myelodysplasia syndrome (MDS), to predict responses to immunosuppressive therapy.

Fluorescent aerolysin

A more accurate alternative reagent for PNH screening and PNH clone measurement is the bacterial toxin aerolysin, which binds to RBCs via GPI anchor and initiates hemolysis. A modified, nonhemolytic form of a fluorescently labeled molecule has been developed that can detect PNH cells to a level of 0.5% (fluorescently labeled inactive toxin aerolysin [FLAER] binding of peripheral blood granulocytes). The advantage of this assay is that it can detect the clone in all hematopoietic cell lineages in one assay.

This is the most specific test for PNH, as FLAER binds the GPI anchor specifically. Thus, the lack of FLAER binding to granulocytes (measured by flow cytometry) is sufficient for the diagnosis of PNH. The disadvantage of the test is in measuring binding in the absence of adequate granulocytes, such as in severe aplastic anemia, when the number of circulating granulocytes is extremely low.

Immmunotyping

Peripheral blood is the most suitable specimen for immunophenotyping for PNH, and it is important to screen both RBCs and granulocytes, because RBC transfusions are common among these patients and granulocytes may not be present in severe hypoplastic anemia patients.

Studies have shown that the size of the PNH clone correlates with the risk for venous thrombosis. Patients with less than 50% PNH granulocytes seldom develop thrombosis, whereas patients with larger clone sizes appear to be at great risk and will require anticoagulation.

Acidified serum lysis and Ham test

If performed properly, acidified serum lysis and the Ham test (from Thomas Hale Ham) are reliable ways to diagnose PNH (see image below). Dr. Ham demonstrated that the RBCs in PNH were lysed by complement when normal serum was acidified or activated by alloantibodies.

View Image

The Ham test (acidified serum lysis) establishes the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH), demonstrating a characteristic abnormalit....

The serum pH is lowered to about 6.2 and the magnesium level is adjusted to 0.005 mol/L to achieve maximum sensitivity. The cells that are hemolyzed are the sensitive cells, and those that remain intact are normal cells, indicating 2-3 subpopulations of RBCs in the circulation.

A false-positive test result is seen in congenital dyserythropoietic anemia, type II (hereditary erythroblastic multinuclearity with positive acidified serum tests [HEMPAS]). These patients have a negative sucrose hemolysis ("sugar water test") result. Some normal serum can give a false-negative Ham test result; thus, the sucrose water test is more sensitive but less specific for paroxysmal nocturnal hemoglobinuria (PNH).

Complement lysis sensitivity test

The complement lysis sensitivity test of Rosse and Dacie is a more precise method for diagnosing PNH. RBCs are sensitized with a potent lytic anti-I antigen and hemolyzed with limiting amounts of normal serum as a source of complement.^{[31, 32, 33]} This demonstrates threee groups of RBCs in patients with PNH, including the following:

• PNH I cells are normal in sensitivity to complement
• PNH II cells are moderately more sensitive to complement than normal cells
• PNH III cells are markedly sensitive to complement, requiring one fifteenth to one twentieth of the amount of complement for an equal degree of lysis; this group of cells is increased in patients with more severe PNH, and it is associated with a mean life span of 10-15 days

Sugar water or sucrose lysis test

The sugar water or sucrose lysis test uses the ionic strength of serum that is reduced by adding an iso-osmotic solution of sucrose, which then activates the classic complement pathway, and complement-sensitive cells are lysed. This test is less specific but more sensitive for PNH than the Ham test, because some RBCs hemolyze from autoimmune hemolytic anemias, leukemia, and aplastic anemia to a minor degree. Although the tests are inexpensive and simple to perform, they are more labor intensive and less sensitive due to the short half-life of circulating PNH RBCs.

Other tests for intravascular hemolysis

Other tests to demonstrate intravascular hemolysis include the following:

• Elevated serum lactate dehydrogenase (LDH)
• Elevated reticulocyte count
• Low-to-absent serum haptoglobin
• Hemoglobinuria and hemosiderinuria; however, hemolysis may occur intermittently and hence can be missed easily, depending on when the tests are performed

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Imaging Studies

Thromboses of major veins are best evaluated by radiographic means.

Investigate hepatic vein thrombosis with a routine technetium-99m (^99m Tc) colloid scan of the liver and spleen. This study often reveals diminished function in all portions of the liver except the caudate lobe, which is spared because it is drained by the inferior vena cava rather than the hepatic vein. A magnetic resonance imaging (MRI) study or ultrasonogram can demonstrate the cessation of flow through the hepatic vein or by injection or use of a dye to demonstrate a thrombus in the vein.

MRI with contrast may demonstrate sagittal vein thrombosis.

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Other Tests

PIGA gene mutation analysis is still limited to research laboratories. In addition, although it is very specific, it is still not diagnostic for paroxysmal nocturnal hemoglobinuria (PNH).

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Approach Considerations

According to current understanding of paroxysmal nocturnal hemoglobinuria (PNH), the ideal treatment is to replace the defective hematopoietic stem cell with a normal equivalent by hematopoietic stem cell transplantation (HSCT); however, this is not realistic for many patients, because HSCT requires a histocompatible donor and is associated with significant morbidity and mortality.^[34] HSCT is reserved for severe cases of PNH with aplastic anemia or transformation to leukemia, both of which are life-threatening complications.

In most cases, treatment instead involves the control of symptoms with agents that inhibit components of the complement system. Several monoclonal antibodies (ie, eculizumab, ravulizumab, crovalimab) that target the C5 complement component have been approved for treatment of PNH by the US Food and Drug Administration (FDA). A monoclonal antibody that inhibits C3, pegcetacoplan, has also been approved for treatment of PNH. 

Iptacopan, an oral inhibitor of factor B (a component of the alternative complement pathway) was approved by the FDA in 2023. It is indicated as monotherapy for PNH.^{[35, 36, 37]}

Danicopan, a selective inhibitor of complement factor D, was approved by the FDA in 2024 for patients who experience clinically significant extravascular hemolysis, as an add-on to C5 inhibitor therapy (eg, eculizumab, ravulizumab).^[38]   

Indications for allogeneic HSCT include persistent hemolysis, persistent thrombosis, and associated marrow failure. A review by Cooper et al of HSCT in 55 patients with PNH reported minimal to no graft versus host disease in 2 patients who received eculizumab after HSCT; these authors suggest that this warrants further study.^[39]

Treatment of bone marrow hypoplasia

Bone marrow hypoplasia is a serious cause of morbidity and mortality. It is treated most effectively with HSCT; however, if no suitable donor is available, antithymocyte globulin (ATG) has been used in the treatment of aplastic anemia with considerable success.^[40]

Treatment of thromboembolism

Patients with PNH who develop acute thrombosis should immediately be started on eculizumab or ravulizumab, if they are not already taking it, as this reduces the risk of thrombosis extension or recurrence.^[13] Otherwise, management of thrombotic complications follows standard principles, including using heparin emergently, then maintenance therapy with an oral anticoagulant, such as warfarin. Sometimes, heparin can exacerbate the thrombotic problem, possibly by activating complement. This can be prevented by using inhibitors of the cyclooxygenase system such as aspirin, ibuprofen, or sulfinpyrazone.

Primary prophylaxis of thromboembolism for patients with PNH has been advocated. Whether this approach is safe and effective in all patients with PNH remains controversial, however.

Corticosteroids

Modulation of complement is controlled poorly by high doses of glucocorticoids. The usual adult dose of prednisone is 20-40 mg/d (0.3-0.6 mg/kg/d) given daily during hemolysis and changed to alternate days during remission. On this regimen, about 70% of adult patients experience improvement in hemoglobin levels, but long-term therapy is fraught with complications.

Investigational agents

A variety of agents that inhibit complement are under development for treatment of PNH. Novel anti-C5 agents include monoclonal antibodies and an anti-C5 small interfering RNA.^[41]  Other inhibitors of complement factor D are also being studied.^{[41, 42]}  

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Complement Inhibition

Several monoclonal antibodies that target complement have been approved for use in PNH. Eculizumab, ravulizumab, and crovalimab are humanized monoclonal antibodies that target terminal complement protein C5. Each agent have been shown to decrease intravascular hemolysis, reduce the need for blood transfusions, and improve PNH-related symptoms such as fatigue.^{[43, 44, 45, 46, 47, 48]}  

Eculizumab and ravulizumab are administered intravenously, but eculizumab is infused every 2 weeks and ravulizumab is infused every 8 weeks. Subcutaneous administration of ravulizumab may considered for maintenance therapy. Crovalimab loading doses are administered as IV infusions, and then by subcutaneous injection every 4 weeks. 

Pegcetacoplan targets complement protein C3, and can control both intravascular and extravascular hemolysis. It is administered by subcutaneous infusion.

Iptacopan is the first oral monotherapy approved for treatment of PNH. It is a factor B inhibitor that acts proximally in the alternative complement pathway, providing control of RBC destruction within and outside of blood vessels (intra- and extravascular hemolysis).^{[35, 36, 37]}

Danicopan, a selective inhibitor of complement factor D, is indicated for patients who experience clinically significant extravascular hemolysis. It is used as an add-on to C5 inhibitor therapy (eg, eculizumab, ravulizumab).^[38]   

Complement inhibitor use

At least 2 weeks before initiating complement inhibitors, vaccinate patients against encapsulated bacteria, including Streptococcus pneumoniae and Neisseria meningitidis (serogroups A, C, W, Y and B), according to current Advisory Committee on Immunization Practices (ACIP) recommendations.

If urgent therapy is needed for a patient who is not current with aforementioned vaccines, prescribe antibacterial drug prophylaxis and administer these vaccines as soon as possible. 

Patients receiving complement inhibitors may develop meningococcal disease despite vaccination or antimicrobial prophylaxis. Often these infections involve nongroupable N meningitidis, whichtypically does not cause invasive disease in immunocompetent individuals. Consequently, clinicians need a high index of suspicion for these infections, and patients should be educated about this risk.^[49]

Eculizumab

Eculizumab (Soliris) alleviates the intravascular hemolysis associated with PNH and its sequelae, dramatically improving symptoms, improving quality of life, and eliminating complications of PNH.^{[9, 50]}  Eculizumab does not alter the underlying defect of the disease, however; thus, treatment needs to continue lifelong or until spontaneous remission, which occurred only in a minority of patients (12 of 80 patients in one study^[23] ) before the advent of eculizumab.

The efficacy and safety of eculizumab has been demonstrated in two multinational phase III trials and a multinational extension study.^[2] Long-term analysis showed that PNH improvements can be maintained over 3 years  in patients on eculizumab, and erythropoietin can overcome anemia due to bone marrow failure.^[48]  The 5-year survival of patients with PNH prior to eculizumab therapy in a cohort followed at Leeds Hospital in the United Kingdom was 66.8%. With eculizumab therapy, 5-year survival improved to 95.5%, which is not statistically different from age-matched controls in the general population.^[51]  

Treatment breakthrough from complement control can occur in small minority (10%) of patients due to an inadequate dosing schedule. The eculizumab level must remain above 35 μg/mL, but trough levels at 2 weeks may fall below this level and cause recurrence of hemolysis. The recommended adjustment for patients whose eculizumab levels fall into this category is to increase the dose to 900 mg every 12 days or 1200 mg every 2 weeks.

If therapy is stopped for any reason, withdrawal hemolysis can occur. Therapy protects type II and III PNH cells from destruction, allowing these cells to accumulate. When eculizumab is stopped and this protection is lost, the resulting hemolysis may be massive. 

Ravulizumab 

In both C5 inhibitor–naïve patients with PNH and those previously treated with eculizumab, ravulizumab (Ultomiris) has proved non-inferior to eculizumab across all efficacy endpoints.^{[45, 46, 52]}  In addition, ravulizumab has a low incidence of breakthrough hemolysis compared with eculizumab.^{[53, 54, 55]}  Because of this lower incidence, ravulizumab has been shown to be more cost-effective than eculizumab. Patient acceptance is also high, because of the less-frequent dosing.^{[55, 56, 57]}  

The US Food and Drug Administration (FDA) approved ravulizumab in 2018 for treatment of adults with PNH.^[58] Ravulizumab gained FDA approval in 2021 for treatment of PNH in children aged 1 month and older. Effectiveness was evaluated in a 26-week study enrolling 13 pediatric patients aged 9-17 years with PNH. Five of the 13 patients were complement inhibitor-naïve and 8 patients had received eculizumab. After the 26-week study, 60% of patients who had not previously received complement inhibitors avoided a transfusion, as did all the patients who had received prior eculizumab.^[59]  

In 2022, the FDA approved a subcutaneous (SC) formulation of ravulizumab for the treatment of adult patients with PNH. The efficacy of the SC formulation was established in a phase III study in 136 patients with PNH who had previously been treated with eculizumab. For 71 days, 90 patients received SC ravulizumab and 46 received intravenous (IV) ravulizumab, thereafter, all patients received SC ravulizumab. At day 71, the amount of ravulizumab in the blood of patients taking SC ravulizumab was no less than in patients taking IV ravulizumab. Serum free C5 concentrations were maintained below the target threshold (< 0.5 mcg/mL) in all patients throughout the one year of SC treatment. Adverse effects were comparable to IV ravulizumab.^[60]  

Crovalimab 

Crovalimab (Piasky) is a monoclonal antibody that binds to complement protein C5, resulting in inhibiting its cleavage into C5a and C5b and preventing formation of membrane attack complex (MAC). This inhibits terminal complement-mediated intravascular hemolysis in patients with PNH. It was approved in June 2024 for patients aged 16 years and older with PNH.  

Approval was supported by the phase III COMMODORE 2 and COMMODORE 3 clinical trials. In COMMODORE 2 (N = 204), crovalimab was shown to be noninferior to eculizumab for hemolysis control (79.3% vs 79%).^[43]  In the single-arm COMMODORE 3 study, 51 complement-naïve patients showed significant hemolysis control and transfusion avoidance from baseline through Week 25 (P< 0.001).^[44]  

Pegcetacoplan

Pegcetacoplan (Empaveli) binds to complement protein C3 and its activation fragment C3b, thereby regulating C3 cleavage and generation of downstream effector of complement activation. It is administered as a SC infusion twice weekly.

The phase III PEGASUS trial included patients with PNH who were still anemic despite at least 3 months of eculizumab therapy. Pegcetacoplan proved superior to eculizumab with respect to the change in hemoglobin level from baseline to week 16, with an adjusted mean difference of 3.84 g/dL (P< 0.001). A total of 35 patients (85%) receiving pegcetacoplan no longer required transfusions, as compared with 6 patients (15%) receiving eculizumab. The most common adverse events were injection site reactions, diarrhea, breakthrough hemolysis, headache, and fatigue.^[61]  

PRINCE, a phase III, randomized, open-label, controlled trial, demonstrated the benefit of pegcetacoplan in treatment-naïve patients with PNH (53 treated patients and 18 controls). Compared with controls, pegcetacoplan rapidly and significantly stabilized hemoglobin and reduced lactate dehydrogenase (LDH) levels and had a favorable safety profile.^[62]

Wong and colleagues conducted a matching-adjusted indirect comparison (MAIC) using patient data from the PRINCE trial and aggregate data from the ALXN1210-PNH-301 trial. The results of the comparison found pegcetacoplan was associated with statistically significant improvements in most clinical endpoints compared with ravulizumab or eculizumab treatment.^[63]  

Iptacopan 

Iptacopan (Fabhalta) is a factor B inhibitor that acts proximally in the alternative complement pathway. It provides control of RBC destruction within and outside of blood vessels (intra- and extravascular hemolysis) by regulating C3 cleavage. It is indicated as oral monotherapy for adults with PNH. Approval was supported by the phase III APPLY-PNH and APPOINT-PNH trials.^{[35, 36, 37]}

In APPLY-PNH, patients who had a mean Hb < 10 g/dL despite receiving anti-C5 therapy for at least 6 months were randomized to receive iptacopan 200 mg twice daily or continue their anti-C5 regimen for 24 weeks. Patients could then opt to enter a 24-week extension period, continuing on iptacopan or switching from anti-C5 to iptacopan monotherapy. In patients in the iptacopan arm, the improvements seen at 24 wks were sustained at 48 wks, with a mean increase in Hb of 3.35 g/dL from baseline. Patients who switched from anti-C5 to iptacopan had rapid improvement in hemoglobin levels, with a mean increase in Hb of 3.36 g/dL from baseline.^[35]   

In the APPOINT-PNH trial, which enrolled treatment-naïve patients, 62.5% of patients (25 of 40) achieved a complete response to iptacopan by Week 24. In APPLY-PNH, by comparison, complete response rates at Week 24 were 71% in the iptacopan arm (44/62) versus 0% in the anti-C5 arm.^[36]  

Danicopan 

Danicopan is indicated for PNH in patients who experience clinically significant extravascular hemolysis, as an add-on to C5 inhibitor therapy with eculizumab or ravulizumab. It selectively inhibits complement factor D. 

In PNH, intravascular hemolysis is mediated by the terminal membrane attack complex (MAC), while extravascular hemolysis is facilitated by C3 fragment opsonization. Danicopan acts proximally in the alternative pathway of the complement cascade to control preferentially C3 fragment–mediated extravascular hemolysis, while co-administered ravulizumab or eculizumab is anticipated to maintain control over MAC-mediated intravascular hemolysis.

Approval was supported by results from the phase III ALPHA trial that compared the addition of danicopan (n = 42) to ravulizumab or eculizumab or the addition of placebo (n = 21). At week 12, hemoglobin had increased by 2.94 g/dL in the danicopan arm compared with 0.5 g/dL in the placebo arm (P< 0.0001).^[38]   

Emergency treatment

Patients with PNH might require urgent treatment in the event of thrombosis or acute kidney injury (AKI). Specialist consultation should be sought where possible.

Acute thrombosis

Anticoagulation therapy with heparin or low-molecular-weight heparin is still the first action to take in the setting of a new thrombotic event. Complement inhibition therapy with eculizumab should be commenced within 24 hours of any new thrombotic event, wherever possible, to reduce the risks of propagation of the thrombotic insult, recurrence, and subsequent long-term complications. Because eculizumab seems to provide protection against the propagation of thrombosis or the occurrence of further thrombotic events, it is our opinion that the development of a PNH-related thrombosis is one of the primary indications to initiate eculizumab therapy.^[64]

In patients with PNH, the management of Budd-Chiari syndrome, which may occur despite anticoagulant prophylaxis, is complex. Immediate initiation of eculizimab does not reliably restore hepatic blood flow. Thrombolytic therapy has also been used, but hemorrhagic complications remain a concern; however, thrombolytic therapy is less likely to be required if eculizumab is started. The risk of developing hepatocellular carcinoma is increased after an episode of Budd–Chiari syndrome; thus, patients should receive routine screening, such as regular blood tests for α-fetoprotein or liver ultrasound scans.^{[65, 66]}

Acute kidney injury

Management of AKI involves hydration, supportive care, and occasionally hemodialysis. A Doppler ultrasound scan is recommended to rule out renal vein thrombosis. Although AKI can be reversible, end-stage kidney disease or ongoing progressive kidney damage can ensue. Long-term eculizumab therapy can contribute to improved kidney function.^[67]

Effect on thromboembolic complications

Complement inhibitor treatment reduces the risk of clinical thromboembolism in patients with PNH (the leading cause of death in PNH) and is recommended for PNH patients with a history of prior thromboembolism.^[68] The rate of thrombotic complications prior to eculizumab was 5.6 per 100 patient years; after eculizumab, it dropped to 0.8 per 100 patient years.

In an international multi-institutional cooperative study involving 195 PNH patients, the thromboembolic (TE) event rate per 100 patient-years with eculizumab treatment was 1.07, compared with 7.37 events (P< 0.001) prior to eculizumab treatment, a relative absolute reduction of 85%. With equalization of duration of exposure before and during treatment for each patient, TE events were reduced from 39 before eculizumab to 3 during eculizumab (P< 0.001). The TE event rate in antithrombotic-treated patients (n = 103) was reduced from 10.61 to 0.62 events/100 patient-years with eculizumab treatment (P< 0.001).

One study has documented elevated D-dimer levels in PNH patients with a history of thrombosis. D-dimer levels decreased immediately after initiation of eculizumab therapy.^[69]

Continuation of anticoagulation in patients with PNH with a previous thrombosis while on eculizumab is recommended, as stopping therapy has not been studied. However, patients with no previous thrombosis have discontinued warfarin after starting eculizumab, with no thrombotic sequelae.^{[70, 71]}

Kidney dysfunction

Chronic hemosiderosis and/or microvascular thrombosis from PNH causes kidney dysfunction or damage at an incidence of 65%, defined by stages of chronic kidney disease (CKD), in a large cohort of PNH patients. Eculizumab treatment was safe and well-tolerated in patients with kidney dysfunction or damage and resulted in the likelihood of improvement as defined as categorical reduction in CKD stage (P< 0.001) compared with baseline and placebo (P = 0.04).^[72]

Improvement in kidney function was more commonly seen in those with less severe impairment. Improvements occurred quickly and were sustained for at least 18 months of treatment. Administration of eculizumab to patients with kidney dysfunction or damage was well tolerated and was usually associated with clinical improvement.^[72]

Iron

Monitoring iron levels is recommended, even if the patient no longer requires transfusions, because hemosiderinuria — a protective mechanism in PNH to excrete iron — no longer occurs with eculizumab. Measuring serum ferritin is recommended and chelation therapy may be necessary in patients with high levels.

• References

Treatment of Anemia

The anemia of PNH may have three components: intravascular hemolysis, inadequate erythropoiesis, and superimposed iron deficiency (massive iron loss through hemoglobinuria). In view of the increased rate of erythropoiesis, give 5 mg/d of folic acid orally. Assess iron stores with the use of the transferrin saturation index (TSI) and give oral ferrous sulfate if the result is < 20%. (Ferritin levels should not be used for this purpose, as ferritin is an acute-phase reactant and levels can be misleading.)

Determine steady-state hemoglobin levels after correction for iron deficiency. When appropriate, transfuse packed red blood cells (RBCs) with leukocytes depleted by filter. Washing RBCs is no longer necessary, and use of irradiated blood products is recommended for future stem cell transplantation.

Supportive care for severe anemia includes blood transfusion using leuko-depleted packed RBCs to prevent alloimmunization. Development of alloantibodies can be a problem with future transfusions because of activation of complement and delayed hemolysis of transfused blood.

Iron

Replacement of nutritional iron, because of increased loss of iron from the hemolysis and the 200-fold increase in iron urinary excretion, is necessary to prevent development of iron deficiency. Iron replacement can stimulate reticulocytosis that can trigger hemolysis by releasing a new cohort of complement-sensitive cells. This process can be prevented by adding prednisone during replacement therapy.

Stimulation of erythropoiesis using androgenic hormones has been successful in patients with a moderate decrease in RBC production. This approach has been replaced mainly with the use of recombinant erythropoietin therapy.

• References

Hematopoietic Stem Cell Transplantation

In severe cases of paroxysmal nocturnal hemoglobinuria (PNH) with an aplastic phase, referral to a hematopoietic stem cell transplantation (HSCT) center is indicated for possible allogeneic HSCT. Umbilical cord stem cell transplantation from the patient's own cord blood, from a related donor, or from the registry for HLA–matched unrelated donors may be an option in pediatric patients.

HSCT using allogeneic donors is the only curative therapy for PNH. With the advent of eculizumab, the indications for HSCT have changed. Clinical results from HSCT from various programs in a rare disease are limited to small numbers of patients. A retrospective analysis of the Italian bone marrow transplantation group in 26 patients with a median age of 32 years (22-60 y, range) with 23 HLA-identical donors (22 siblings, one unrelated) shows a transplant-related mortality of 42%, 8% graft failure, and a 10-year survival (disease-free) of 57% for all patients.^[73] The mortality rate remains high, so this form of therapy is reserved for those who are severely hypoplastic and refractory to other forms of therapy.

The International Bone Marrow Transplant Registry (IBMTR) reported a 2-year survival probability of 56% in 48 recipients of HLA-identical sibling transplants between 1978 and 1995.^[74] Data using nonmyeloablative conditioning and haploidentical donors was similar to the identical donors, indicating some form of graft-versus-PNH effects. Now that an effective, nontransplant therapy is available, the use of allogeneic HSCT to treat PNH has decreased.

Before the introduction of eculizumab, PNH patients with severe symptoms from classic PNH and patients with aplastic anemia/PNH with peripheral cytopenias meeting criteria for severe aplastic anemia were considered good candidates for allogeneic HSCT, especially if a matched sibling donor was available.

With eculizumab for PNH, the indications for allogeneic HSCT in this setting have changed. First, HSCT should not be offered as initial therapy for most patients with classic PNH, given the high transplant-related mortality, especially when using unrelated or mismatched donors. Exceptions are PNH patients in countries where eculizumab is not available. HSCT is also a reasonable option for patients who do not have a good response to eculizumab therapy. Second, aplastic anemia/PNH patients continue to be reasonable candidates for HSCT if they have life-threatening cytopenias.^[34]

An analysis by the International PNH Interest Group reviewed data from 67 patients from single centers and from two registry studies, with special emphasis in eliminating duplication in patient reporting.^[27] Results included the following:

• Of the seven patients transplanted from a twin syngeneic donor, the four who had no conditioning therapy either failed to engraft or relapsed after transplantation, indicating that marrow ablative conditioning is necessary before syngeneic transplantation.
• In 47 of 67 patients, a human leukocyte antigen (HLA)-identical sibling was used as the donor, 1 from a haploidentical family member and 12 from an unrelated donor (matched unrelated donor [MUD]).
• In the only single-center study providing a Kaplan-Meier analysis, overall survival at 5 years was 58 ± 13%. This is less favorable than the survival estimate of approximately 75% generated by combining the data from the other reports.
• Investigation is currently in progress regarding whether reduced-intensity conditioning can improve the outcome.

A retrospective study of 21 PNH patients who underwent HSCT after previous treatment with eculizumab found that HSCT was associated with almost 30% mortality, mainly due to infections and acute graft-versus-host disease (GVHD). Syngeneic HSCT transplants were well tolerated. The authors suggested that these results may call into question the role of HSCT for patients with classic PNH who continue to require transfusions despite eculizumab, in the absence of a syngeneic donor.^[75]

• References

Treatment in Pregnancy

Pregnancy in patients with PNH poses very significant risks. There is a very high risk of thrombotic complications for the expectant mother, as well a risk of developing hypoplastic anemia. Maternal mortality in these patients is approximately 20%, mostly from thrombosis and infections, and risk of fetal loss is increased. Consequently, full anticoagulation with low-molecular-weight heparin (LMWH) is recommended for pregnant women with PNH. Warfarin may be substituted after the first trimester.

The use of eculizumab in pregnancy has proved beneficial.^[76] In a review of 75 pregnancies in 61 women with PNH, Kelly and colleagues reported a high rate of fetal survival and a low rate of maternal complications. No maternal deaths occurred. There were three fetal deaths (4%) and six first-trimester miscarriages (8%). During pregnancy, patients demonstrated increased requirement of red blood cell transfusions, and approximately half required an increase in the eculizumab dosage. Ten hemorrhagic events occurred, and two postpartum thrombotic events. Eculizumab was detected in some infants' cord blood, but not in breast milk.^[77]

No information is available regarding the presence of eculizumab in human milk, the effects on the breastfed infant, or the effects on milk production. No information is available on the use of ravulizumab during breastfeeding, but the manufacturer recommends against breastfeeding during ravulizumab therapy and for 8 months after the final dose.^[78]

• References

Complications

Primary care physicians should be aware of the thrombotic complications of paroxysmal nocturnal hemoglobinuria (PNH) and how to diagnose them when they occur.

Kidney complications

Chronic hemolysis and renal iron deposition, which is a particular risk in PNH when complement inhibition therapy is delayed or not available, may result in acute tubular injury or acute kidney injury (AKI). Consultation with a nephrologist may be indicated to help manage these cases. Continuous renal replacement therapy (CRRT) is one of the best options for the treatment of PNH-associated AKI. Dialysis techniques may include immunoadsorption, dedicated hemodialysis filters that use convective techniques, backfiltration, or coupled plasma filtration adsorption (CPFA).^[79]

• References

Long-Term Monitoring

Patients with PNH on eculizumab therapy should be monitored regularly, for several reasons. First, the underlying bone marrow failure might progress and require treatment; second, to confirm that intravascular hemolysis is well controlled; and third, to monitor the proportion of PNH cells.

In the small percentage of patients who have spontaneous remission of PNH, therapy can be discontinued. Rarely, the abnormal PNH clone may eventually disappear. This usually takes at least 5 years, and often as long as 15-20 years. Reactivation of PNH in these patients has been observed with acute infections. Patients with chronic anemia alone, without thrombotic complications, can live relatively normal lives for many years. However, occasionally what appears to be a spontaneous remission might actually be evolving transformation and careful reassessment is required.^[80]

Continued anemia due to inadequate response to eculizumab is common and its reason should be explored. In true refractory cases, the patients had mutant complement C5 that prevented eculizumab binding. An alternative complement inhibitor is desirable for these patients, with trial enrollment if available. Bone marrow failure is a common cause and concomitant immunosuppressive therapy can be safely administered if necessary. 

Furthermore, up to 20% of patients might require a higher dose of eculizumab to maintain terminal complement blockade during the 14-day interval between infusions. This situation often presents clinically as a return of PNH-related symptoms (abdominal pain, dysphagia and dark urine) 1–2 days before the next infusion is due. However, the patient might also be relatively asymptomatic and the underdosing can only be uncovered by the need for transfusions or raised lactate dehydrogenase (LDH) levels. Thus, it is useful to check LDH levels on the day of the infusion and increase the eculizumab dose if necessary to reduce the risks of PNH-related complications and transfusion requirements.^[81]

Plasma products should be avoided in patients on eculizumab therapy, because they contain high levels of complement proteins. If the administration of plasma products is required (for example, in cases of trauma or substantial hemorrhage), eculizumab will need to be re-administered.

Low-level extravascular hemolysis is present in the majority of patients treated with eculizumab. No intervention is usually necessary, but patients might need occasional red blood cell transfusions. Patients who experience clinically significant extravascular hemolysis can be treated with danicopan as an add-on to C5 inhibitor therapy.

Patients with iron overload also have reduced hematopoiesis, which can limit improvement in the hemoglobin level. Adequate hematinic replacement should be provided: folate supplementation as required and exogenous erythropoietin (the hormone that stimulates erythropoiesis) administration if erythropoietin levels are inappropriately low for the degree of anemia.

If the hemoglobin level temporarily falls during treatment for anemia, usually in association with an infection, three scenarios should be considered:

• Suppression of bone marrow hematopoiesis (as seen in the setting of many infections
• Increased extravascular clearance of red blood cells (which is also often associated with infections)
• Breakthrough of terminal complement blockade due to increased complement activity

The first two situations require appropriate anti-infective and supportive measures only and do not result in increased PNH-associated complications. The third situation, however, could require attempts to restore terminal complement blockade to avoid complement-induced thrombosis or kidney damage. During strong complement activation (for example, in certain infections), intravascular hemolysis might occur owing to a conformational change in C5 that limits the ability of eculizumab to block C5 convertases. In this situation, treatment may need to shift to a C3-blocking antibody preparation (ie, pegcetacoplan).

Occasional outpatient RBC transfusion often is necessary to keep a patient with PNH and chronic anemia able to function and live a normal life. Discontinuing anticoagulation therapy when a patient is on effective doses of eculizumab has been increasingly performed worldwide, and there is little concern about recurrence of thrombotic events as long as the patient is routinely monitored.^[82]

• References

Medication Summary

The agents used in treatment of paroxysmal nocturnal hemoglobinuria (PNH) include the following:

• Complement inhibitors (eg, pegcetacoplan, eculizumab, ravulizumab, crovalimab, iptacopan, danicopan), to stop hemolysis
• Recombinant erythropoietin or androgens, to stimulate erythropoiesis
• Anticoagulants, to treat thrombotic complications
• Immunosuppressive agents, to stimulate hematopoiesis in the aplastic phase

• References

Ravulizumab (Ravulizumab-cwvz, Ultomiris)

• Dosing, Interactions, etc.

Clinical Context:  Indicated for paroxysmal nocturnal hemoglobinuria (PNH) in adults, adolescents, and children as young as 1 month. Long-acting IV product that allows for every 8 week dosing starting 2 weeks after a single loading dose in patients weighing at least 20 kg. Every 4 week dosing is needed if weight less than 20 kg. May be administered SC for maintenance treatment in adults. 

• References

Eculizumab (Bkemv, Eculizumab-aagh, Eculizumab-aeeb)

• Dosing, Interactions, etc.

Clinical Context:  Indicated for adults with paroxysmal nocturnal hemoglobinuria (PNH) to reduce hemolysis. After weekly IV loading doses over 5 weeks, maintenance doses are administered every 2 weeks.

• References

Crovalimab (Crovalimab-akkz, Piasky)

• Dosing, Interactions, etc.

Clinical Context:  Indicated for patients with PNH aged 13 years and older who weigh at least 40 kg.

• References

Pegcetacoplan (Empaveli)

• Dosing, Interactions, etc.

Clinical Context:  Indicated for adults with paroxysmal nocturnal hemoglobinuria (PNH). Administered as a twice weekly SC infusion. After proper training in SC infusion, the patient/care-giver may administer, if the healthcare provider deems appropriate. 

• References

Iptacopan (Fabhalta)

• Dosing, Interactions, etc.

Clinical Context:  Binds to Factor B of the alternative complement pathway and regulates C3 cleavage, generation of downstream effectors, and terminal pathway amplification. Iptacopan acts proximally in the alternative pathway of the complement cascade to control both C3b-mediated extravascular hemolysis and terminal complement-mediated intravascular hemolysis. It is indicated as oral monotherapy in adults with PNH.

• References

Danicopan (Voydeya)

• Dosing, Interactions, etc.

Clinical Context:  Indicated for paroxysmal nocturnal hemoglobinuria (PNH) in patients who experience clinically significant extravascular hemolysis (EVH), as an add-on to complement component-5 (C5) inhibitor therapy (eg, eculizumab, ravulizumab). It selectively inhibits complement factor D. 

In PNH, intravascular hemolysis (IVH) is mediated by the terminal membrane attack complex (MAC), while extravascular hemolysis (EVH) is facilitated by C3 fragment opsonization. Danicopan acts proximally in the alternative pathway of the complement cascade to control preferentially C3 fragment–mediated EVH, while co-administered ravulizumab or eculizumab is anticipated to maintain control over MAC-mediated IVH. 

• References

Class Summary

Pegcetacoplan binds to complement protein C3 and its activation fragment C3b, thereby regulating C3 cleavage and generation of downstream effector of complement activation.

Other monoclonal antibodies (ravulizumab, eculizumab, crovalimab) bind downstream in the complement cascade to C5 with high affinity inhibit cleavage to C5a (proinflammatory anaphylatoxin) and C5b (initiating subunit of the terminal complement complex [C5b-9]). The prevents generation of the terminal complement complex C5b9. This action inhibits terminal complement-mediated intravascular hemolysis in patients with PNH.

Iptacopan is a factor B inhibitor that acts proximally in the alternative complement pathway of the immune system. 

Danicopan selectively inhibits complement factor D and is used in combination with ravulizumab or eculizumab in patients with PNH who experience clinically significant extravascular hemolysis (EVH). 

All of these agents carry Black Box warnings regarding increased risk of meningococcal infection. Because of that risk, they are available only through a restricted program, under a Risk Evaluation and Mitigation Strategy (REMS), which providers must enroll in. 

• References

Oxymetholone (Anadrol-50)

• Dosing, Interactions, etc.

Clinical Context:  Anabolic and androgenic derivative of testosterone in an oral formulation.

Used to stimulate erythropoiesis by increasing endogenous levels of erythropoietin and by enhancing the response of precursor cells to the growth factor.

• References

Danazol

• Dosing, Interactions, etc.

Clinical Context:  Synthetic steroid analogue, derived from ethisterone, with strong antigonadotropic activity (inhibits LH and FSH) and weak androgenic action without adverse virilizing and masculinizing effects. Increases levels of C4 component of the complement. May push the resting hematopoietic stem cells into cycle, making them more responsive to differentiation by hematopoietic growth factors. May also stimulate endogenous secretion of erythropoietin.

May impair clearance of immunoglobulin-coated platelets and decreases autoantibody production.

• References

Class Summary

Androgens are used to stimulate erythropoiesis by increasing endogenous levels of erythropoietin and by enhancing the response of precursor cells to the growth factor.

Attenuated androgens, such as danazol, are recommended for use in women, as the attenuated androgen has fewer adverse virilizing and masculinizing effects.

• References

Antithymocyte globulin rabbit (ATG rabbit, Thymoglobulin)

• Dosing, Interactions, etc.

Clinical Context:  Off-label use for PNH. Purified preparation of pasteurized polyclonal IgG obtained from rabbits immunized against human thymocytes (T cells) for IV use. This preparation has replaced the equine preparation (Atgam) on the market and is considered an equivalent.

• References

Class Summary

Antithymocyte globulin is an antiserum to human T cells.^[40] The mechanism of action of polyclonal antilymphocyte preparations to suppress immune responses is not fully understood.

• References