Onychomycosis and the diagnostic significance of nail biopsy

Onychomycosis is the most common cause of deformed nails. It is often confused clinically with other nail diseases such as psoriasis. A cross sectional study was carried out in 120 clinically suspected onychomycosis patients to assess the diagnostic utility of nail unit histopathology. The majority of the patients were males (72.5%) in the age group of 20-40 years (55%). Involvement of fingernails alone (37.5%) was found to be more common than toenails (12.5%). Distal and lateral subungual onychomycosis [DLSO] (76.6%) was the predominant morphological type noted. Direct microscopy with 10% potassium hydroxide (KOH) preparation revealed fungal filaments in 82.5% of the cases. Mycological culture on Sabouraud's dextrose agar with and without cycloheximide indicated fungal isolates in 44% of the cases, with Trichophyton mentagrophytes being the most common isolate (38.3%). The combined approach with KOH preparation and culture showed the evidence of fungus in 103 cases (85.8%). Of the rest of the 17 cases in whom both these procedures failed to confirm a diagnosis, nail unit biopsy was carried out in 15 consenting patients. Fungal hyphae (better demonstrable on PAS staining) were evident in 14 cases (93.3%). Other histopathological features observed among these patients were subungual hyperkeratosis, neutrophilic infiltrate, parakeratosis, hemorrhage, and serum crusts. We concluded that histopathological examination of nails is a valuable diagnostic aid in onychomycosis, especially if routine parameters fail to establish a diagnosis.