Eruptive vellus hair cysts
Published Web Locationhttps://doi.org/10.5070/D37nh4m6jt
Eruptive vellus hair cystsNew York University Department of Dermatology
Julie K Karen MD, Marissa Heller MD, Sue Ann Wee MD, Radha Mikkilineni MD
Dermatology Online Journal 13 (1): 14
A 20-year-old man presented with multiple, asymptomatic, follicular papules that were distributed over his abdomen. Microscopic examination showed classic features of a vellus hair cyst. The term eruptive vellus hair cysts refers to a benign condition, which may be inherited or acquired. Apart from occasional pruritus, cosmetic disability is the chief concern of most patients. An estimated 25 percent of lesions remit spontaneously; however, treatment of persistent lesions is often challenging with disappointing results.
A 20-year-old man presented to the Dermatology Clinic at Bellevue Hospital Center for evaluation of multiple, small, asymptomatic papules that were localized to his abdomen. The patient estimated that the lesions had appeared approximately 3 years previously. Medical history included ulcerative colitis, for which he had recently received a 1-month course of oral prednisone. His medications included mesalamine, mercaptopurine, lansoprazole, ferrous sulfate, and folic acid. No family members had similar lesions. A biopsy was performed to confirm the diagnosis.
Numerous, 1-2 mm, flesh-colored-to-bluish-gray, follicular, nontender, non-pruritic papules were distributed over the abdomen.
|Figure 1||Figure 2|
Histopathology reveals small dermal cysts lined by stratified squamous epithelium and containing transversely sectioned vellus hair shafts. There is surrounding fibrosis and granulomatous inflammation secondary to rupture of the cyst wall.
The term eruptive vellus hair cysts (EVHC) was introduced in 1977 in a report of two pediatric patients with multiple, asymptomatic, monomorphous, hyperpigmented papules that were distributed on the trunk and flexor aspects of the extremities. Histopathologic examination showed intradermal cysts that contained keratinous material and multiple fragmented vellus hairs .
EVHC may occur sporadically or be inherited in an autosomal dominant fashion . The majority of cases are isolated and benign findings. However, there are reports of EVHC occurring in association with renal failure and with such disorders as anhidrotic ectodermal dysplasia, hidrotic ectodermal dysplasia, pachyonychia congenita, and Lowe syndrome [3, 4, 5, 6, 7].
EVHC demonstrates no sex or racial predilection. The literature contains reports of the onset of EVHC ranging from birth to adulthood [8, 9]. Generally, in familial cases, lesions are first noted at birth or shortly thereafter, whereas the usual age of onset is between 4 and 18 years in the acquired form. The precise pathogenesis of EVHC is unknown; however, some postulate that developmental abnormalities predispose vellus hair follicles to infundibular occlusion. Follicular occlusion leads to retention of hairs, proximal cystic dilatation, and consequent atrophy of the hair bulb .
Classically, EVHC manifests with multiple, 1-4 mm, smooth, dome-shaped, asymptomatic papules. Sites of predilection include the anterior chest and extremities; however, the abdomen, back, neck, axillae, groin, and face may also be affected. There are reports of generalized  and of isolated facial  variants in the literature. Lesions may appear hyperpigmented, flesh-colored, yellow, erythematous, or blue. Rarely, lesions are umbilicated or hyperkeratotic . The vast majority of cases are asymptomatic; however, there are reports of associated tenderness  or pruritus .
The clinical differential diagnosis includes steatocystoma multiplex (SM), milia, keratosis pilaris, folliculitis (i.e., microbial, sterile, or perforating), infundibular cysts, trichilemmal cysts, dermoid cysts, acne cysts, and molluscum contagiosum. Overlapping histopathologic features and reports of EVHC and SM appearing together in the same patient have led some to posit an etiologic link between these two entities .
Diagnosis of EVHC is confirmed by examination of a cutaneous biopsy specimen, which shows a mid-dermal cyst that contains laminated keratin and multiple transversely- and obliquely-cut vellus hairs. A flattened squamous epithelium lines the cyst wall. Ruptured cysts demonstrate a granulomatous reaction in the adjacent dermis . An alternative, less invasive diagnostic approach has been described in which a superficial incision at the top of the lesion enables expression of the cystic contents. Microscopic examination of the expressed contents in a potassium hydroxide preparation shows numerous vellus hairs .
Although generally an asymptomatic and innocuous condition, EVHC can be cosmetically bothersome. Spontaneous resolution occurs in an estimated 25 percent of lesions and is thought attributable either to transepidermal elimination  or to granulomatous dissolution . Treatment of persistent lesions is challenging and oftentimes disappointing. Modest benefit has been achieved with 12 percent lactic acid and retinoids . Mild improvement has been reported with the use of an abrading sponge followed by the application of 10 percent urea cream . Neither oral isotretinoin (1 mg/kg for 20 weeks), nor vitamin A therapy has been successful . Surgical techniques, which include excision, curettage, needle evacuation, and incision and drainage, have been utilized but are time consuming and may result in scars. Other destructive modalities, which include dermabrasion and laser therapy using a CO2 or erbium:yttrium-aluminum-garnet (Er:YAG) laser, have been employed. These approaches enable rapid treatment of multiple lesions; however, their utility is limited by inconsistent results and an increased risk of scars [23, 24].
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