Post-Traumatic Single-Digit Onychomycosis.

Onychomycoses are a group of fungal nail infections commonly classified either according to the pathogenic fungus, to the duration of the disease or to the mode of fungal invasion. Most cases are diagnosed clinically, although there is a general consensus that the pathogen should be identified prior to initiating a treatment. However, this is often difficult as the classical mycologic methods of direct microscopy and culture frequently remain negative. We came across a particular subset of onychomycoses, which posed extreme diagnostic and therapeutic challenges. Over a period of 15 years, 44 patients were seen in specialized nail clinics with a single nail dystrophy that was examined and treated in vain by many practitioners and dermatologists prior to their consultation. Of the forty-four cases, thirty-nine patients had a fingernail affected and five had a toenail affected. The nail was almost completely onycholytic, the nail bed visibly keratotic, the proximal nail fold smooth and shiny and slightly swollen. All patients except five brought the results of negative mycologic cultures. Thirty-four patients had received antifungal therapy, mostly topical, as a single nail would not qualify for systemic treatment according to most national and international guidelines. The diagnosis was finally confirmed by histopathology of the nail plate showing an invasive onychomycosis in all cases. After nail avulsion and combined topical and systemic antifungal therapy, thirty-six patients were cured, three were lost from follow-up, and five showed improved nails but not a complete clinical and mycologic cure. A single-digit nail disease raises the suspicion of a tumor or a trauma; although, in rare cases, diseases normally affecting several nails may only affect a single nail. Such a case should prompt the clinician to ask for a previous trauma to this digit and to intensify the search for a specific pathogen. This study also underlines the importance of histopathology for the diagnosis of onychomycoses.