Comparative study for the reliability of potassium hydroxide mount versus nail clipping biopsy in diagnosis of onychomycosis

Introduction: The clinical pictures of nail dystrophies caused by different fungi are seldom diagnostic. Mycological confirmation with appropriate diagnostic techniques including direct microscopy and fungal culture is important to ensure correct diagnosis and treatment. Microscopy can be performed using potassium hydroxide (KOH) mount and histological evaluation of nail plate specimens with the periodic acid Schiff (PAS) method. Aim: This study was designed to compare KOH/DMSO (Dimethylsulfoxide) preparation with PAS of nail clippings in the diagnosis of onychomycosis. Patients and methods: Forty patients with clinically suspected onychomycosis were included. Every patient was subjected to clipping of the distal free edge of the nail plate, along with any attached subungual debris for PAS staining and histopathological examination. Another enough sample of subungual debris to which a drop of KOH/DMSO solution was added on a slide and examined using × 10 and × 40 magnification. Both PAS stained and KOH/DMSO mount samples were evaluated for the presence of hyphae and/or spores. Results : Among the 40 patients, only 30 proved to be KOH positive while 23 of PAS stained samples were positive. KOH mount has a sensitivity of 75% versus 57.5 % for PAS staining. Statistically, there was no significant differences between the two methods regarding test sensitivity (p=0.098). Conclusion: KOH test could be considered as a first line preliminary tool in diagnosis of onychomycosis while PAS staining can be used as a confirmatory method. KEywORDS: Onychomycosis, KOH mount, periodic acid Schiff (PAS) Dalia Shaaban and Zeinab Abd El-Samad INTRODUCTION Onychomycosis (OM) is the most common nail disorder and is present in 2% to 13% of general population increasing up to 48% by 70 year of age.1 Onychomycosis generally caused by dermatophytes is often symptomatic and can cause functional impairment. The clinical presentation of OM involves hyperkeratosis with thickening and discoloration of the nail plate. Other disorders such as nail psoriasis, lichen planus, OM and nail trauma may yield a nearly identical picture.2 An accurate diagnosis of OM is important because systemic antifungal therapy is often indicated which carries an additional expense and is occasionally associated with adverse events and drug interactions.3 It is necessary to confirm the clinical diagnosis with sufficient laboratory evidence before initiating oral antifungal treatment. Direct demonstraCorrespondence: Dr. Hassab-El-Naby, MD, Dermatology, Venereology & Andrology Department, Faculty of Medicine Al-Azhar University, Cairo, Egypt