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Case Reports

Abstract

An 81-year-old male with a history of multiple keratinocyte carcinomas presented with a 1.1 cm pink, scaly, flat-topped plaque on the left lateral foot. Clinically, the lesion was favored to be squamous cell carcinoma, prurigo nodularis, or a plantar verruca. A shave biopsy was performed which showed acral skin with large columns of hyperparakeratosis with underlying intraepidermal dyskeratosis, consistent with cornoid lamellae. However, within the cornoid lamellae, numerous fungal hyphae were also identified. A PAS stain confirmed the presence of these hyphae but also that only very rare hyphae were present in the background stratum corneum away from the cornoid lamellae. Further review of the clinical images showed findings consistent with background tinea pedis, and the patient’s medical record showed a long-standing history of this diagnosis as well. However, why would the fungal hyphae localize to the cornoid lamellae in such a manner? Tinea pedis is extraordinarily common, so the background milieu is certainly not the problem. There must be something inviting about the abnormal parakeratin produced within a cornoid lamella that is particularly attractive to hyphae. Tinea seems to enjoy unusual keratinization at baseline, be it the compact acral stratum corneum of tinea pedis or subungual keratin of onychomycosis. Perhaps the tightly fitted parakeratotic cells of the cornoid lamella are a perfect fit for tinea, a five-star dermatophyte hotel where tinea can thrive, snugly ensconced in a high-rise of keratin. This unique architecture likely mandates the use of topical keratolytics in addition to standard antifungal agents.