Pachyonychia congenita-associated alopecia. A microscopic analysis using transverse section technique.

Pachyonychia congenita (PC) is a rare genodermatosis with characteristic nail abnormalities and occasional palmoplantar keratoderma and leukokeratosis oris; alopecia may occur (10% of patients). This report is the first microscopic description of a patient with PC-associated alopecia. Transverse section histologic features include diminished follicular density with preservation of follicular units, prominent miniaturization of follicles, dyskeratosis of outer root sheath keratinocytes, and moderate parakeratotic and orthokeratotic follicular hyperkeratosis. These microscopic features may be seen individually in other nonscarring alopecias, but the combination may be unique to PC-associated alopecia. Differential diagnoses include alopecia areata, androgenetic alopecia and traction alopecia/ trichotillomania.