Eruptive Vellus Hair Cysts: An Underdiagnosed Entity.

Eruptive vellus hair cyst (EVHC) is a rare follicular developmental abnormality of the vellus hair follicles. The usual onset is between 17 and 24 years but may be congenital. It can arise sporadically or may be inherited in an autosomal dominant fashion. They are caused by an abnormality at the infundibular level of vellus hairs. They usually appear as yellow to reddish-brown papules over the chest, limbs, and abdomen. Histologically, cyst has a stratified squamous epithelium and it contains lamellated keratin and several vellus hairs. We present this rare case of a 12-year-old male because of its unusual morphology and distribution and also to generate awareness about this rarely diagnosed condition. To the best of our knowledge, no case of an axillary variant of EVHC has been reported till date. Copyright:

INTRODUCTION

Eruptive vellus hair cyst (EVHC) represents the developmental abnormality of vellus hair follicle. It is defined as occlusion and cystic dilatation of the hair follicles. Cysts are characteristically located in the mid dermis and contain a variable amount of lamellated keratin and multiple transversely and obliquely cut vellus hairs. They are uncommon benign tumors of the pilosebaceous unit. We are reporting this rare case of a 12-year-old male due to its unusual presentation of multiple EVHCs over the axilla and forehead along with other common sites such as trunk and extremities.

CASE REPORT

A 12-year-old boy presented with multiple, asymptomatic light-colored lesions over the flexor aspect of upper extremities, the chest, axilla, and forehead for 6 months. Few lesions resolved on their own, leaving behind postinflammatory hyperpigmentation. The patient denied the use of any cosmetic product, excessive sun exposure, and any mechanical trauma. There was no family history of similar lesions.

Physical examination revealed discrete, symmetrically distributed, 1–2 mm sized, dome-shaped, pale yellow follicular papules, over the flexor aspect of both upper extremities, the axilla, chest, and a single lesion over the forehead [Figure 1]. Oral, genital, and nail examinations were normal.

Figure 1

Multiple pale-yellow follicular papules, with few hyperpigmented papules over the flexor aspect of both upper extremities (1a, 1b), the chest, axilla, and forehead

Differential diagnosis of milia, steatocystoma multiplex (SM), EVHCs were considered.

A skin punch biopsy from the papule showed a mid-dermal cyst, lined by thinly stretched epithelium and had a corrugated lining. Granular layer was absent. Abundant lamellated keratin and several vellus hair shafts were present within the cyst [Figure 2]. On serial sections, there were no sebaceous glands noted adjacent to or within the cell wall.

Figure 2

Histopathology with H and E (×10) and (×100) showing a mid-dermal cyst lined by thinly stretched epithelium, that lacks granular layer and has a corrugated lining in foci and abundant lamellated keratin and several vellus hair shafts are present within the cyst

Thus, the diagnosis of EVHC was confirmed. We started him on topical tretinoin cream (0.05%) daily at night. He is currently under the follow-up period.

DISCUSSION

EVHC was first described by Esterly, Fretzin, and Pinkus in 1977. The exact cause of EVHC is unknown. Some consider it as an unusual developmental abnormality of vellus hair follicles, predisposing them to occlusion at the level of infundibulum, resulting in the retention of hair, cystic dilatation of the proximal part of the follicle, and secondary atrophy of hair bulbs. While some authors believe it to be a hamartoma differentiating toward vellus hairs.

EVHCs are either sporadic or inherited in autosomal dominant fashion. In sporadic occurrence, they appear in the first and second decades of life. It can affect both genders equally, and there is no ethical or racial difference.

EVHC most commonly presents as numerous, small, skin-colored to darkly pigmented, and dome-shaped papules with soft to firm consistency. A central hyperkeratotic crust, central puncta, and umbilication have been described in a few lesions. In general, they are asymptomatic, but occasionally they may be associated with itching or tenderness. Distribution most commonly involves the chest, abdomen, and extremities. Occasionally, lesions may also occur over the face, neck, groins, and axilla.[1]

Associations of EVHCs with SM, trichostasis spinulosus, anhidrotic ectodermal dysplasia, eccrine poromas, sebaceous adenomas, Lowe syndrome, and pachyonychia congenita have been reported.[2]

Histologically, EVHCs are characteristically located in the mid dermis. The cyst is lined by stratified squamous epithelium with epidermoid keratinization. The cyst cavity contains a variable amount of loose lamellated keratin and multiple transversely and obliquely cut vellus hairs.[3] The cyst wall may be present in continuity with a rudimentary hair follicle or arrector pili muscle. In general, no sebaceous glands are present in the cyst wall.

The differential diagnosis of pilosebaceous cysts includes infundibular cysts, SM, and EVHCs.[4] These can be differentiated by different immunohistological patterns and staining properties with KRT10 and KRT17. SM expresses both KRT10 and KRT17, whereas EVHC expresses only KRT17.[5]

Alternatively, a simple rapid diagnostic test has been described in which the cyst was incised, and the contents of the cyst were expressed. Microscopic examination of the expressed contents with 10% potassium hydroxide shows numerous vellus hairs.[6]

Most lesions persist if untreated, but approximately 25% of cases may undergo spontaneous resolution due to transepidermal elimination of cyst contents and inflammatory destruction.

Patients generally seek medical advice for cosmetic reasons. Treatment modalities include incision and drainage, needle evacuation with an 18G needle. Patients may benefit from topical keratolytic agents such as retinoic acid (0.05%), tazarotene (0.1%), urea (10%), or lactic acid (12%). Other modalities include laser ablation using CO2 or Erbium-yttrium-aluminum-garnet but should be used cautiously as it may lead to scarring.[78]

CONCLUSION

Eruptive vellus hair cyst is an underdiagnosed and underreported benign tumor of the pilosebaceous unit. So histopathological examination should always be done in all suspected cases of EVHC to differentiate it from other similar conditions.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.