Eruptive vellus hair cysts were first described in 1977 by Esterly et al in the case of 2 children with a hyperpigmented monomorphous papular eruption of several years’ duration.1 Since then, various cases of vellus hair cysts, or eruptive vellus hair cysts, have been described in the literature.
Eruptive vellus hair cysts are typically found in children and young adults. Males and females are equally affected, and no racial predilection exists. Eruptive vellus hair cysts may have onset in infancy, suggesting that an autosomal-dominant inheritance pattern may exist.2 Thus, cases are often familial when occurring early in life and sporadic when occurring in young adulthood. No associations between vellus hair cysts and other skin conditions have been identified, suggesting that they are usually an isolated skin finding. However, vellus hair cysts tend to arise in children with other medical conditions, such as eccrine poromas, sebaceous adenomas, anhidrotic ectodermal dysplasia, hidrotic ectodermal dysplasia, and pachyonychia congenita. As a result, physicians should include vellus hair cysts in the differential diagnosis for patients who have these conditions and are presenting with papules.3
When a blockage occurs at the infundibulum of a hair follicle, just below the epidermis, the hair follicle is at risk for cystic dilatation. This subsequently causes atrophy of the bulb of the hair, resulting in a vellus hair cyst.4 A hamartoma that is differentiating toward vellus hair represents another possible etiology. 4 Familial cases are postulated to involve a mutation in keratin genes.4 Amid the above hypotheses, the true cause of eruptive vellus hair cysts remains unknown.
Clinically, eruptive vellus hair cysts appear as a collection of discrete follicular papules, each measuring approximately 1 to 4 mm in size. The appearance of these papules varies widely from brown to gray, blue, yellow, or even erythematous in appearance. The chest, flexor and extensor surfaces of the arms and legs, and the back are the most common sites of involvement. Rarely, the papules can be seen on the ear, face, vulvar labia, abdomen, and axilla. Most lesions are smooth, but cases of umbilication, hyperkeratosis, and epidermal elimination have been described.4
Histologically, biopsy specimens demonstrate a mid-dermal cyst that is lined with stratified squamous epithelium that is approximately 2 to 5 cells thick. Laminated keratin and multiple vellus hairs are identified within the cyst. Granulomatous inflammation may be present, especially if the vellus hairs are in contact with the cyst wall. Typically, there are no sebaceous glands in the cyst wall.5
The differential diagnosis of vellus hair cysts is relatively broad and should include steatocystoma multiplex, dermoid cysts, folliculitis, perforating folliculitis, keratosis pilaris, milia, molluscum contagiosum, acne vulgaris, trichostasis spinulosa, and syringoma, as many of these medical conditions can resemble vellus hair cysts.4,6,7 Additionally, the above lesions may often affect the chest and resemble small papules or nodules.
Due to the rarity and resemblance of vellus hair cysts to other conditions, the diagnosis is best made via histologic analysis following punch biopsy. If the biopsy has vellus hairs, as well as other histologic characteristics mentioned above, then the diagnosis can be made. Another method for diagnosis involves puncturing the skin with a blood-collecting needle to aspirate the contents of the cyst or removing the entire cyst using forceps. Following this, a potassium hydroxide wet mount of cyst contents is analyzed, which may also reveal vellus hairs.8
Treatment of vellus hair cysts is often challenging and unfortunately yields varying results. First, there is no standard treatment for eruptive vellus hair cysts. The lesions can be removed with incision and drainage using an 18-gauge needle for evacuation after the application of local and topical anesthesia. However, scarring is a potential complication of this treatment method. Topical modalities include retinoic acid (0.05%), tazarotene cream (0.1%), urea (10%), or lactic acid (12%). Dermabrasion, erbium:yttrium aluminum garnet laser ablation, and carbon dioxide laser vaporization have shown improvement in some cases. Studies using oral isotretinoin have shown no response. Although untreated lesions generally tend to persist, they can spontaneously regress as a result of transepidermal elimination in approximately 25% of individuals.4,6
For the patient in the case described, a biopsy of 1 of the lesions yielded findings that were consistent with an eruptive vellus hair cyst. Since the same dermatologic manifestations were also present in the patient’s mother, the case was deemed a familial case. The patient is currently using retinoic acid as treatment, but she has not noticed results. If the lesions persist after a course of topical retinoic acid, the patient would like to try a laser treatment or incision and drainage.
Click to the next page for Case 2.