Comparative Study between Polymerase Chain Reaction and Conventional Methods Used for Diagnosis of Clinically Suspected Onychomycosis

Background: Proper treatment of onychomycosis depends mainly on accurate diagnosis. Diagnosis using conventional methods (direct microscopy and culture) is still insensitive and time consuming so we aimed to evaluate the commercially available PCR as a rapid method used for detection of fungal elements especially Trichophyton rubrum in nail specimens with clinically suspected onychomycosis and compare the results with conventional diagnostic methods.

Methodology: This study included 50 patients with clinically suspected onychomycosis of nails. Nail specimens were obtained by scraping of the diseased nail(s) with a sterile scalpel blade and collected in a sterile container. Each specimen was divided into 3 portions and processed immediately or kept at room temperature until use. The first part was examined by direct microscopy with 20% KOH, the second part was cultured on Sabouraud dextrose agar (SDA) and the third part was subjected to pan-fungal PCR for detection of fungal infection followed by specific PCR for identification of T. rubrum.

Results: Regarding all fungal isolates KOH microscopy, culture and pan-fungal PCR respectively yielded positive rates of 27 (54%), 26 (52%) and 37 (74%). Pan-fungal PCR picked up 11 specimens missed by culture. Regarding T. rubrum, KOH microscopy, culture and T. rubrum specific PCR respectively yielded positive rates of 3 (6%), 11 (22%) and 20 (40%). T. rubrum specific PCR picked up 9 specimens missed by culture. Of the 26 specimens that were culture positive, 14 grew dermatophytes, 9 Candida spp and 3 non-dermatophytic molds. These results emphasize the superiority of PCR over conventional methods.

Conclusion: This study demonstrates that both pan-fungal and T. rubrum specific PCR have higher positive rates for detection of fungal infections of the nails compared with KOH microscopy or culture. We suggest that PCR should be used as a complementary method for confirmation of clinically suspected onychomycosis.