Abstract

Subungual epidermoid cysts (SEC) are rare benign cystic lesions of the nail bed. There has been only one case series describing SEC. We report nine cases of SEC (eight cases from our institution and one consultation case), the clinical differential diagnosis includes cutaneous horn, wart, atypical nevus, pigmented lesion, fungal infection and squamous cell carcinoma. The patients had a mean age of 65-years (range 3-84) with F: M ratio of 1.25. Four occurred in toenails and five in fingernails. A history of prior trauma was reported in 4/9 patients. The presentation varied from pain, discoloration, erythronychia, black streaks or white spots on nails, elevation of the nail plate, subungual hyperkeratosis, thickening and shortening of nail plates. All the cases involved a single digit. Co-existing onychomycosis was present in 1/9 cases.

Histologically, all demonstrated by small cystic cavities lined by epidermal type squamous epithelium with a complete or interrupted granular layer and keratin fragments within the cystic cavities. The keratinocytes exhibited light pink cytoplasm with ovoid, uniform nuclei. The case with the interrupted granular layer had overlapping features with an onycholemmal cyst.

6/9 s were treated with nail avulsion and two underwent amputation due to unrelated underlying medical conditions. Follow-up data available for 8/9 cases (mean follow-up period = 71 months) demonstrated no recurrences. SEC are benign but symptomatic lesions that should be distinguished from other subungual nail bed lesions such as onycholemmal cysts, onychomatricoma, subungual squamous cell carcinoma and subungual keratoacanthoma.