Proximal Subungual Onychomycosis in the Immunocompetent: A Case Report and Review of the Literature.

Proximal subungual onychomycosis (PSO), which predominantly involves the nail plate from the proximal nail fold, is the rarest form of onychomycosis. Classically associated with an immunocompromised state, PSO is an uncommon diagnosis in individuals without immunodeficiency. We present a case of a healthy 51-year-old man, who presented with a three-month history of white discoloration of multiple toenails. Physical examination revealed white, opaque patches on the proximal third nail plates of multiple toenails. The affected digits also demonstrated proximal onycholysis, subungual debris, and mild paronychia. Laboratory examinations, including routine serologic studies as well as human immunodeficiency virus and antinuclear antibodies, were within normal limits. Proximal nail fragments of the left hallux showed sections of dystrophic nail plate with mounds of parakeratosis, collections of neutrophils, and hyphae that highlighted with periodic acid-Schiff staining. The patient was diagnosed with PSO and tinea pedis bilaterally and treated with oral fluconazole with gradual improvement. This case of PSO highlights the potential for its rare occurrence in a healthy host. However, the clinical presentation of PSO should trigger an evaluation for possible immunodeficiency. <p><em>J Drugs Dermatol. 2018;17(4):475-478.</em></p>.