Comparative Evaluation of Conventional and Molecular Methods for the Diagnosis of Onychomycosis.

Background Onychomycosis is a common fungal infection of the nail that often presents diagnostic challenges. Conventional laboratory methods such as microscopy and culture may show limited sensitivity, leading to delayed diagnosis and treatment. Molecular methods such as polymerase chain reaction (PCR) may improve diagnostic accuracy. Objectives To compare different diagnostic methods for onychomycosis by evaluating their sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). Methods This cross-sectional descriptive study was conducted from July 2023 to June 2024 at Sir Salimullah Medical College (SSMC), Dhaka. A total of 139 nail samples were collected from patients with clinically suspected onychomycosis attending the outpatient department of Dermatology and Venereology. The samples were examined by potassium hydroxide (KOH) mount microscopy, fungal culture, acridine orange stain fluorescence microscopy, periodic acid-Schiff (PAS) stain, and PCR. Laboratory investigations were conducted in the Department of Microbiology at SSMC and at Bangladesh Medical University (BMU). Culture was considered the gold standard, and the diagnostic performances of other methods were evaluated. Results Among the 139 samples, KOH mount microscopy detected 65 (46.79%) cases, PAS stain detected 31 (22.30%) cases, acridine orange fluorescence microscopy detected 68 (48.92%) cases, and PCR detected 98 (70.50%) cases. Dermatophytes were isolated in 70 (50.36%) cases and Candida albicans in 11 (8%) cases, with Trichophyton mentagrophytes being the most common species. Compared with culture, PCR demonstrated the highest sensitivity (97.53%) and NPV (95.12%), while PAS stain showed the highest specificity (96.55%). Conclusion PCR demonstrated superior sensitivity compared with conventional diagnostic methods and may facilitate early and accurate diagnosis of onychomycosis when applied directly to clinical samples.