Fungal Melanonychia as a Solitary Black Linear Vertical Nail Plate Streak: Case Report and Literature Review of Candida-Associated Longitudinal Melanonychia Striata

Longitudinal melanonychia striata, presenting as a black linear vertical band of the nail plate, can be caused by pigmented lesions and non-pigmented etiologies. A fungal infection of the nail plate, also referred to as onychomycosis or tinea unguim, can result from dermatophytes, non-dermatophyte molds, and Candida. Albeit rare, Candida-associated fungal melanonychia can present as a longitudinal black nail plate streak. The case of a 79-year-old man who developed a solitary linear black streak on his right fourth fingernail after a prior history of recent trauma to the digit’s nail folds is described; the fungal culture grew Candida parapsilosis. Including our patient, Candida-associated longitudinal melanonychia striata has been described in four women and two men ranging in age from 40 to 79 years (median, 70 years) at diagnosis. The black streak, present from one month to one year (median, seven months), affected either a hand digit (five patients) or the great toe (one patient). Fungal organisms were visualized on either a potassium hydroxide preparation (one patient), pathologic evaluation of a nail plate specimen (three patients), or both (one patient). Culture grew Candida parapsilosis (two patients), Candida species (two patients), Candida albicans (one patient), and Candida tropicalis (one patient). All of the patients experienced clinical improvement after treatment. Topical treatment (5% amorolfine hydrochloride nail lacquer for two patients or modified Castellani paint and 1% clotrimazole cream for one man) or oral itraconazole (either as monotherapy for two women or combined with 5% amorolfine hydrochloride nail lacquer for one woman) was successfully used. Although the clinical presentation of fungal melanonychia can mimic subungual melanoma when it appears as a solitary black linear vertical nail plate streak, investigative studies--such as a potassium hydroxide preparation, nail plate pathology, nail matrix biopsy, and/or fungal culture--can be used to establish the diagnosis of Candida-associated longitudinal melanonychia striata and exclude the diagnosis of a pigmented melanocytic tumor.