PAS is optimal for diagnosing onychomycosis.

Onychomycosis is a frequently treated fungal infection of the nail plate with morbidity in high-risk populations. The diagnosis often relies on histopathologic analysis of nail plate specimens with the assistance of special stains. Pathologists utilize periodic acid schiff (PAS) and/or Gomori methenamine silver (GMS) stains to highlight fungi within the nail plate. In a recent study of 51 PAS-negative nail cases, it was concluded that GMS is superior to PAS in the diagnosis of onychomycosis. We expand on this study by investigating a larger number of PAS-negative nail clippings determining whether GMS or PAS is superior in highlighting fungi in additional sections. There was no difference in the sensitivity of PAS vs. GMS (4.2 vs. 4.3%, p = 0.57); however, PAS was found to be significantly less expensive by 2.6-fold. Taken together, these data suggest that the PAS stain is the optimal method for diagnosing onychomycosis.