Korean J Dermatol.  2021 Sep;59(8):618-623.

Histopathological Examination of the Nail Plate and Comparison between Periodic Acid-Schiff and Gomori’s Methenamine Silver Stains for the Diagnosis of Onychomycosis

• Baek G
• Koo T
• Lee D
• Kang HJ
• Kim MS
• Kim Y
• Jue MS

Abstract

Background
A direct potassium hydroxide (KOH) smear is used to diagnose onychomycosis despite its broad sensitivity range. For a more accurate diagnosis, histopathologic examination can be used and consistently show high sensitivity.
Objective
We investigated the value of histopathologic examination of the nail plate as a diagnostic tool for onychomycosis. We proposed effective routine diagnostic staining to compare sensitivity between periodic acid-Schiff (PAS) and Gomori’s methenamine silver (GMS) staining.
Methods
This retrospective study was conducted from January 1, 2019 to May 31, 2020, and included 97 patients who showed negative results on direct KOH smear but had clinical manifestations that implied onychomycosis. We performed nail plate biopsy and PAS or GMS staining to identify fungal hyphae missed in the direct KOH smear. Sensitivity comparison between PAS and GMS was performed in co-stained samples.
Results
Among 97 patients with 102 cases, 55 cases (53.9%) of onychomycosis were confirmed by histopathologic examination. A total of 68 patients (70.1%) had a previous medical history of antifungal agents within previous six months. PAS and GMS staining were concurrently performed in 73 cases, and onychomycosis was confirmed in 41 cases. The sensitivity of PAS was 100% (41/41), while that of GMS was 87.8% (36/41); this difference was not significant.
Conclusion
This study suggests that histologic examination of the nail plate is an effective tool to diagnose onychomycosis and can be performed with a direct KOH smear. Two staining methods, PAS and GMS, are recommended for concurrent performance to enhance the identification of fungal hyphae.

Keyword

Methenamine; Onychomycosis; Pathology; Periodic acid