Performance of mycology and histopathology tests for the diagnosis of toenail onychomycosis due to filamentous fungi: Dermatophyte and non‐dermatophyte moulds

Improvement of laboratory diagnosis of onychomychosis is important so that adequate treatment can be safely implemented. To evaluate and compare the performance of mycological and histopathological examinations in onychomycoses caused by dermatophyte and non‐dermatophyte moulds. Patients with lateral/distal subungual onychomycosis in at least one hallux were enrolled in the protocol and assessed via mycological and histopathological tests. The isolation of filamentous fungi was considered the gold standard. Test performance was evaluated through sensitivity, specificity and positive and negative predictive values. A total of 212 patients were enrolled in the study. Direct microscopy (DM) was positive in 57.5% patients, and cultures in 34.4%. Among these patients, 23.3% were positive for dermatophytes, with Trichophyton rubrum the most frequently isolated, and 86.3% were positive for non‐dermatophytes, with Neoscytalidium dimidiatum predominance. Histopathology was positive in 41.0% samples. Direct microscopy showed better sensitivity for non‐dermatophyte moulds (P=.000) and nail clipping was more specific for dermatophyte (P=.018). Histopathology of the distal nail plate is a valuable complementary tool for the diagnosis of onychomycosis caused by dermatophytes and direct microscopy is especially useful for non‐dermatophyte molds.