Practice Essentials
Halo nevi are common benign skin lesions that represent melanocytic nevi in which an inflammatory infiltrate develops, resulting in a zone of depigmentation surrounding the nevus. They are entirely benign lesions and of only cosmetic significance.
Because melanoma that has undergone regression may appear gray or white, halo nevi have been erroneously confused with melanoma and can be the source of much anxiety among both clinicians and patients.[1]
Pathophysiology
The etiology is unknown, but halo nevus is believed to be due to an immune response against melanocytes. Numerous studies have attempted to unravel the immunologic mechanisms by which an immune response develops to existing aggregates of nevus cells.[2] The infiltrating cells are predominantly T-lymphocytes, and cytotoxic (CD8) lymphocytes outnumber helper (CD4) lymphocytes by a ratio of approximately 4:1. These, as well as scattered macrophages, comprise most inflammatory cells in halo nevi.[3] As seen in vitiligo, melanocytes in the epidermis in the halo component of the nevus are completely absent, suggesting a similar etiologic mechanism.[4]
A distinct relationship seems exist that distinguishes halo nevus in patients without vitiligo and halo nevus in patients with vitiligo, although definitive features have not been determined. Multiple halo nevi, the presence of Koebner phenomenon, and a family history of vitiligo have been identified as possibly increasing the risk of vitiligo in patients with halo nevi.[5]
Nevus excision may prevent progression to vitiligo vulgaris. In a study of 54 patients with excised halo nevus, the presence or absence of vitiligo vulgaris was associated with improvement in the surrounding vitiligo following excision.[6]
The exact role that the lymphocytes play in the regression of halo nevi has not been fully determined, although a theory of direct cytotoxic effects on melanocytes seems plausible.
Of interest, circulating antibodies to the cytoplasm of melanoma cells have been detected in patients with halo nevi.[7] Because these antibodies have disappeared after removal of the halo nevus, they were thought to be related. Subsequent investigation failed to reveal a temporal relation between the appearance of these antibodies and the regression of nevus cells, and these antibodies are now believed to appear as a consequence of the release of cytoplasmic proteins of halo nevus melanocytes secondary to cell damage.
Ultrastructurally, advanced lesions of halo nevus show dermal macrophages containing portions of nevus cells. While it is clear that an immunologic mechanism results in the demise of melanocytes in halo nevi, the precipitating cause and the exact role of the lymphocytes remain unknown.[8]
Cases of halo nevi developing following intermittent intense sun exposure have been reported suggesting ultraviolet exposure may have a role in the etiology.[9]
Epidemiology
Frequency
The incidence of halo nevi in the population is estimated to be 1%.[10] Patients with Turner syndrome have been reported to have an increased incidence of halo nevi.[11]
Race
All races are susceptible to the development of these lesions. A familial tendency for halo nevi has been reported.
Sex
No sexual predilection is reported.
Age
Halo nevi are found most commonly in children.[12] The average age of onset is 15 years.
Prognosis
Halo nevi are benign. Morbidity is minimal and limited to cosmetic appearance. Because halo nevi are benign, the prognosis for patients is excellent. The course of halo nevi is normally uncomplicated. Problems arise in those instances where the lesions have been misdiagnosed or when the lesion is excised and wound complications develop postoperatively.
Patient Education
Patients should be instructed to monitor the lesion. If changes occur that suggest irregularity or if such symptoms as bleeding, itching, pain, or ulceration develop, the patient should be reevaluated promptly to exclude the possibility of cutaneous melanoma. For patient education resources, see the patient education article Mole Removal.
History
Patients with halo nevi are usually asymptomatic. The central nevus may or may not involute with time. Repigmentation often takes place over months or years; however, it does not always occur. Occasionally, inflammation occurs with crusting in the depigmented zone of a halo nevus. Most commonly, the chief complaint is that of a changing mole (or moles).
Physical Examination
Halo nevi are usually single but may be multiple. They can develop anywhere on the body but are seen most frequently on the trunk. Clinically, they appear as one or more uniformly colored, evenly shaped, round or oval nevi centrally with even peripheral margins of hypopigmentation. The central nevus may be tan, pink, or brown. The width of the halo is variable but is generally of uniform radial distance from the central nevus.
View Image | Classic appearance of a halo nevus. |
View Image | Note the central pink papule (intradermal nevus) and the surrounding halo. The halo is of uniform width at all points, and no inflammatory component c.... |
Other Tests
Performing an examination using a Wood lamp may aid in differentiating halo nevi from other disorders.
Procedures
Lesions that are not uniform in shape and color or that have a papular component that is not centrally located should be considered for biopsy to exclude the presence of melanocytic atypia.
Histologic Findings
The histology of halo nevus is variable depending on the age of the lesion; however, in most cases, a dense, somewhat bandlike lymphocytic infiltrate is present in the papillary and often reticular dermis with nests of nevus cells located centrally. The lesion usually demonstrates a dome-shaped architecture similar to that seen in noninflamed nevi. Identifying residual nevus cells may be difficult in some cases, particularly with older lesions or those in which the infiltrate is quite dense. Mitotic figures usually are not seen, although occasional apoptotic cells may be identified. Macrophages may be seen within the infiltrate, some of which are laden with melanin, although, surprisingly, the number of melanophages is less than would be expected in an inflamed melanocytic lesion.
View Image | At low magnification, a dome-shaped papular lesion reveals a dense infiltrate of lymphocytes in the dermis (hematoxylin and eosin, original magnificat.... |
View Image | Higher magnification reveals nests of nevus cells with numerous lymphocytes surrounding them and in the interstitium (hematoxylin and eosin, original .... |
In more mature lesions, nevus cells may appear to be absent or decreased in number. Clinically, a noninflammatory halo nevus may demonstrate a halo, but, histologically, virtually no inflammatory infiltrate may be present. Conversely, some nevi may demonstrate marked inflammation, but, clinically, no halo is visible. Therefore, clinical correlation is important in rendering a diagnosis of halo nevus. The most important lesion to differentiate from halo nevus is melanoma (see Table).
Table. Distinguishing Features of Halo Nevus and Melanoma
View Table | See Table |
Approach Considerations
Halo nevi are benign, and no treatment is necessary.
Author
Edward J Zabawski, Jr, DO, MBA, Adjunct Assistant Professor, Clinical Sciences
Disclosure: Nothing to disclose.
Coauthor(s)
Clay J. Cockerell, MD, President and Owner, Cockerell Dermatopathology; Adjunct Clinical Professor, Department of Internal Medicine (Dermatology), Division of Dermatopathology, University of North Texas Health Science Center at Forth Worth
Disclosure: Nothing to disclose.
Chief Editor
Dirk M Elston, MD, Professor and Chairman, Department of Dermatology and Dermatologic Surgery, Medical University of South Carolina College of Medicine
Disclosure: Nothing to disclose.
Additional Contributors
Susan M Swetter, MD, Co-Director, Pigmented Lesion/Melanoma and Cutaneous Oncology Programs, Professor, Department of Dermatology, Stanford University Medical Center and Cancer Institute, Veterans Affairs Palo Alto Health Care System
Disclosure: Nothing to disclose.
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