Histopathological Periodic Acid-Schiff Stains of Nail Clippings as a Second-Line Diagnostic Tool in Onychomycosis

The diagnosis of onychomycosis, using direct microscopy and fungal cultures, is often negative despite the presence of disease. Periodic acid-Schiff (PAS) staining of nail clippings, using histopathological processing, may be positive in these cases. It is not always clear, however, whether the fungal elements detected by PAS staining are pathogenic fungi or some are saprophytes. We aimed to study the efficacy of histopathological PAS staining of nail clippings as a second-line diagnostic tool in onychomycosis. The study included 100 consecutive cases in which direct microscopy and fungal cultures from suspected onychomycosis were negative on one occasion or more. The obtained nail clippings were processed for routine histology, stained with hematoxylin and eosin and PAS, and examined microscopically. Of the 100 cases, 38 (38%) showed positive fungal elements. As a result, 9 patients had sought and received oral antifungal therapy and all achieved complete clinical cure. The histological examination also revealed parakeratosis and globules of plasma, which were statistically significantly more common in the fungal infected nail samples. This may indicate an ongoing inflammatory process associated with onychomycosis. Neutrophils and bacteria were not statistically and significantly more common in the fungal infected nails. We conclude that as a second-line diagnostic tool, PAS stain of nail clippings increases markedly the diagnostic yield of onychomycosis and, consequently, the outcome of therapy.