Interdigital Tinea Nigra.

Tinea nigra is an uncommon superficial dermatomycosis precipitated by Hortaea werneckii, a halophilic and halothermic yeast-like fungus capable of producing a melanin-like substance. This pathogen infiltrates the stratum corneum in the setting of microtrauma and produces an asymptomatic brown to black macule or patch that appears similarly to melanocytic nevi or melanoma. We present a case of a 52-year-old woman who presented to clinic several months after developing a painless, nonpruritic dark brown patch in her left foot inside the fourth toe web. The coloration and location of this lesion would typically prompt biopsy; however, Wood's lamp examination and potassium hydroxide (KOH) preparation were pursued first and demonstrated evidence of infection by H. werneckii. The patient was treated with topical clotrimazole cream and miconazole powder for one month, and her lesions cleared completely. Her lesions did not recur at her three-month follow-up appointment.