Eruptive Vellus Hair Cysts

Background

Eruptive vellus hair cysts (EVHCs) were first described in 1977 by Esterly et al, who reported two children with symmetrically distributed follicular papules on the chest and flexor extremities. Histologically, these papules had the unique characteristic of dermal cysts containing small vellus hairs.^[1]

EVHCs may either be acquired or inherited in an autosomal dominant fashion. Generally, they are isolated findings. In some cases, however, they may be associated with other skin disorders (eg, anhidrotic ectodermal dysplasia, hidrotic ectodermal dysplasia, pachyonychia congenita).

Approximately one quarter of cases resolve spontaneously. Medical treatment, if required, may include keratolytic therapy, retinoids, or calcipotriene. Other treatments include needle evacuation of the cyst, simple excision (though this is impractical in most cases), and laser therapy. (See Treatment.)

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Pathophysiology

EVHCs are thought to arise as a developmental abnormality of vellus hair follicles. A predisposition exists for follicular occlusion at the level of the infundibulum, A gradual disruption occurs between the proximal and distal parts of the follicle, usually at the level of the infundibulum. This results in retention of hairs, cystic dilatation of the proximal follicle, and subsequent secondary atrophy of the hair bulb.^[2]

EVHCs have also been considered a type of follicular hamartoma. The cyst wall may consist of keratinization patterns from different levels of the follicular infundibulum. The keratinization is generally that of the epidermis or the outer root sheath, but foci of trichilemmal keratinization have also been reported.

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Etiology

EVHCs may be either acquired or inherited in an autosomal dominant fashion. A case report described facial EVHCs occurring after topical application of minoxidil.^[3]

Although EVHCs are typically isolated findings, they are sometimes associated with other skin disorders.

A case report described EVHCs in association with syringomas.^[4]

EVHCs have been reported in cases of pachyonychia congenita as well.^{[5, 6]}  Pachyonychia congenita is an autosomal dominant disorder associated with palmoplantar hyperkeratosis, dystrophic nails, oral leukoplakia, follicular hyperkeratosis, and corneal abnormalities. Several cases have been associated with other types of multiple cutaneous cysts (eg, steatocystoma multiplex and epidermoid cysts).

A case report linked EVHCs with hidrotic ectodermal dysplasia.^[7]  The patient had sparse hair and disabling palmoplantar hyperkeratosis. Incidentally, the patient was taking oral etretinate at 1 mg/kg/d for more than 2 years, which resulted in improvement of her keratoderma but did not alleviate the EVHCs.

EVHCs have also been reported in association with anhidrotic ectodermal dysplasia.^[8]  In this condition, patients have a greatly reduced number of eccrine sweat glands and sebaceous glands, experiencing difficulties with temperature regulation as a result. Other clinical features include sparse hair, brittle nails, and teeth abnormalities.

Mieno et al reported two cases of EVHCs occurring in association with renal failure, both of them involving 58-year-old Japanese patients with acquired renal disease on hemodialysis.^[9]  EVHCs were confirmed by skin biopsy from the cervical region in both cases. The authors hypothesized that advanced glycation end product may play a role in the development of the cystic structures in these patients; however, cause and effect were not demonstrated.

A possible link has been suggested between neurologic abnormalities and EVHCs. Morgan et al reported a patient with developmental delay, mild intellectual impairment, and congenital EVHCs.^[10] They cited two other patients with incidental seizure disorders and EVHCs as corroborating evidence; however, at present, there is insufficient evidence to support a new neurocutaneous syndrome involving EVHCs.

One report described EVHC occurring in a patient with Lowe syndrome.^[11] Lowe syndrome is an X-linked recessive oculocerebrorenal syndrome with mutations of Xq24-26.1. The authors suggested that a defect in the oculocerebrorenal-Lowe 1 gene (OCRL1) might account for the cyst formation. Features of Lowe syndrome include renal failure, intellectual disability, and eye abnormalities.

A case report described multiple EVHCs occurring in a patient with Stüve-Wiedemann sundrome.^[12]

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Epidemiology

The true frequency of EHVCs is unknown. As of early 2020, fewer than 200 cases had been reported in the literature^[13] ; however, EVHCs may occur more frequently than reports have suggested,^[14] possibly because definitive confirmation of the diagnosis can be obtained only by means of biopsy.

In familial cases, EVHCs are first noted at birth or during infancy. In sporadic cases, cysts usually develop in the late first or the second decade of life. Males and females are affected equally. No racial predilection has been demonstrated.

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Prognosis

Although EVHCs are asymptomatic, they may be cosmetically bothersome. Morbidity may be associated with treatment of the disorder. Lesions may resolve spontaneously via transepidermal elimination of cyst contents. 

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History

Eruptive vellus hair cysts (EVHCs) typically develop as an acneiform eruption on the chest and extremities.^[15] They have also been reported on the eyelids and periorbital skin, as well as the labium majus.^{[16, 17, 18, 19]} Often, no antecedent trauma or triggering factor is reported. EVHCs may be congenital or acquired. Several familial cases have been reported in which the condition is thought to be inherited as an autosomal dominant trait.^[20]

EVHCs may be present at birth or arise in childhood. In sporadic cases, lesions typically arise in the first and second decades with the onset of puberty.

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Physical Examination

EVHCs are clinically manifested as discrete follicular papules, which may appear erythematous, yellow, bluish-gray, or even slightly brown. (See the images below.) The chest and the flexor or extensor surfaces of the extremities are the most common sites of involvement. They can occur in the axilla.^[14] Generalized EVHCs and facial variants have been reported.^[21] A case report described EVHCs on the face that led to blue-gray discoloration of the skin and mimicked nevus of Ota.^[22] EVHCs may also be seen on the ears.^[23] Unilateral EVHCs of the face have been described.^[24]

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Clinical photo of eruptive vellus hair cysts, showing involvement on patient's chest.

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Eruptive vellus hair cysts in axilla.

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Patient seen here is expanding his cheek with air to better demonstrate multiple eruptive vellus hair cysts on his face.

Although patients may have only a few cysts, they often may have as many as several hundred. More than 400 cysts were seen on one patient with generalized EVHC. The cysts are usually dome-shaped with a smooth surface, measuring 1-4 mm in diameter. They sometimes demonstrate central puncta, hyperkeratotic crusts, or umbilication. Mechanical irritation of the cysts may produce transepidermal elimination of retained vellus hairs, similar to that seen in perforating folliculitis.

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Procedures

Punch biopsy of the skin is the diagnostic procedure of choice for eruptive vellus hair cysts (EVHCs).

Alternatively, the diagnosis can be confirmed with a potassium hydroxide wet mount of cyst contents extruded through a small incision. Microscopic examination of the cyst contents reveals vellus hairs. The cyst can be anesthetized with a local or topical anesthetic prior to incision with a sterile blade or an 18-gauge needle.

In 2006, Kaya et al described an extraction technique in which patients were treated with topical anesthetic before the surface of the cyst was punctured with a sharp-tipped electrocautery instrument.^[25] The cyst wall and contents were then dissected out with forceps and either sent to a pathology laboratory or examined microscopically with 10% potassium hydroxide to confirm the diagnosis of EVHC.

A report by Alfaro-Castellon et al indicated that dermoscopy can help distinguish EVHC from acne and molluscum contagiosum.^[26]

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Histologic Findings

Histopathologic examination of EVHCs reveals a cystic structure in the middermis arising from the infundibulum of a hair follicle.^[27] The cysts contain multiple cross-sections of vellus hairs and layered laminated keratinous material. (See the images below.) They are lined by squamous epithelium that is two to five cells thick. Generally, no sebaceous glands are present in the cyst wall. A surrounding granulomatous reaction may be present, especially if the hairs disrupt the cyst wall.

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Histopathology of eruptive vellus hair cyst, showing middermal cyst with squamous epithelium.

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Close-up view of contents of eruptive vellus hair cyst, showing cross-sections of vellus hairs and laminated keratinous material.

The differential diagnosis of pilosebaceous cysts includes infundibular cysts, steatocystoma multiplex, and EVHCs. All three commonly affect the anterior chest and consist of asymptomatic papules or nodules. Obstructed or occluded follicles form the common infundibular cysts. These do not contain sebaceous glands or vellus hairs. The cysts of steatocystoma multiplex arise in the sebaceous duct and have a crenulated, eosinophilic, hyaline lining to the cyst wall where the granular layer is absent. Steatocystomas also contain sebaceous glands arising within the cyst wall.

Some authors have suggested that EVHC and steatocystoma multiplex are variants of the same disorder, on the grounds that the two lesions have been reported to occur together in the same patient.^[28] Other authors have continued to maintain that these are two distinct entities, on the basis of differences in histologic patterns.

One study showed that EVHC lesions expressed keratins 1 and 10, calretinin, and p63, but findings were negative for epithelial membrane antigen, filaggrin, and androgen receptors.^[29] Another study demonstrated differential expression of keratins 10 and 17.^[30] In two cases of EVHC, strong staining for keratin 17 was found, but no staining for keratin 10 was evident. In seven cases of steatocystoma, both keratin 10 and keratin 17 were expressed in the suprabasal cells of the cyst wall. In five epidermoid cysts, positive staining occurred only for keratin 10.

Certain patients may have cysts containing elements of both EVHCs and steatocystoma multiplex. The term hybrid cyst has been proposed to describe cysts containing combinations of EVHCs, steatocystoma multiplex, and epidermoid cysts.^[31] Some authorities have argued that these cyst types all form from the pilosebaceous unit and therefore all fall along a spectrum of the same disorder. Combinations of infundibular cysts, trichilemmal cysts, and pilomatricomas have also been described as hybrid cysts.

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Medical Care

Approximately 25% of eruptive vellus hair cyst (EVHC) cases resolve spontaneously through transepidermal elimination.

Keratolytic treatment was reported as beneficial after gentle mechanical dermabrasion with an exfoliating sponge (eg, Buf Puf; 3M, St Paul, MN) followed by an application of 10% urea cream. Significant clinical improvement resulted in one case with 12% lactic acid applied to the affected areas.

Retinoid treatment can be helpful. Topical tretinoin applied nightly to the affected area is a reasonably safe treatment option. This method reportedly cleared a case of congenital EVHC after only five applications, leaving only a slight residual erythema that gradually faded. Topical tazarotene cream 0.1% applied to the affected area was shown to be more effective than some surgical options for the treatment of EVHC.^[32]  

Oral isotretinoin (1 mg/kg/day) produced no improvement in one patient after 20 weeks of therapy.^[33]  Systemic vitamin A therapy (100,000 IU/day) has also been tried; however, this also produced no clinical improvement and resulted in severe headaches that necessitated discontinuance of therapy.

The use of calcipotriene to treat EVHCs has been reported. A case report noted a partial response of EVHCs after a 2-month treatment course with topical calcipotriene.^[34]

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Surgical Care

Needle evacuation of EVHCs can be performed via an 18-gauge needle after local anesthesia with a topical anesthetic (EMLA cream). This technique can also be helpful in the diagnosis of EVHC. After extrusion, the cyst is examined histologically, pressed between a glass slide and a cover slip with mineral oil. Multiple thin, fine hairs can be seen within the lumen of the thin cyst wall.

Simple excision (eg, punch biopsy technique) removes the cyst; however, this is not practical for most cases of EVHCs, because the cysts are too numerous and punch biopsy scars may be unsightly.

A case report by Huerter et al described successful use of carbon dioxide laser vaporization to treat EVHCs on the face.^[35] A test spot was performed with the carbon dioxide laser (10,600 nm) at 5 W of power, an irradiance of 160 W/cm², a 2-mm spot size, and a pulse duration of 0.2 s. No scarring occurred after the face was treated in this manner. Eyelid lesions were treated in the same manner, except with only 3 W of power and an irradiance of 100 W/cm². Slight hyperpigmentation occurred at some of the treated sites; no hypertrophic scarring was noted. Cystic regeneration did not occur.

The pulsed erbium:yttrium-aluminum-garnet (Er:YAG) laser (2940 nm) was reported to be effective in treating two patients with EVHCs on the trunk.^[36] The technique employed a 2-mm spot size, a pulse duration of 250 ms at 60.5-63.7 J/cm², and a pulse energy of 1.9-2.0 J. Three to five stacked pulses were delivered, and the cysts were expressed with digital pressure and were extracted with forceps. The base of the cyst wall was further ablated with three pulses, and the area was allowed to heal by secondary intention. In the follow-up evaluation (performed only by telephone interview), patients reported no scarring, discoloration, or recurrence of the cysts.

Another report, however, suggested early recurrence of the cysts after the use of the Er:YAG laser to treat EVHCs on the face.^[37]

A split face study compared the 2940 nm Er:YAG laser with a nonablative 1540 Er:Glass laser.^[38] The treatment period was 9 months, with treatment intervals of 6-12 weeks. The study found a reduction in the total number of cysts, with a tendency toward better clinical outcomes with the Er:YAG ablative laser.

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Tretinoin topical (Altreno, Atralin, Avita)

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Tazarotene (Arazlo, Avage, Fabior)

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Calcipotriene (Calcitrene Ointment, Dovonex, Sorilux)

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Ammonium lactate (AmLactin, Lac Hydrin, Proxymetacaine)

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Urea topical (Aquacare, Carmol 10, Carmol 20)

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