Complementary role of a polymerase chain reaction test in the diagnosis of onychomycosis

Abstract

The successful treatment of onychomycosis depends on accurate diagnosis. Conventional diagnostic methods, including direct microscopy and fungal culture, are non-specific, insensitive and time-consuming. Recently, PCR has shown promise in improving the diagnosis of onychomycosis. We aimed to evaluate a commercially available PCR kit for the in vitro detection of dermatophytes and specifically Trichophyton rubrum in nail specimens with suspected onychomycosis, and to compare the detection rates of PCR with conventional diagnostic methods. Nail specimens were prospectively collected from patients with clinically suspected onychomycosis. All nail specimens were positive on direct microscopic examination. PCR and fungal cultures were administered, and the detection rates of dermatophytes were compared. In all, 107 nail specimens were analysed. The fungal culture was positive in 57 (53%) specimens (38 dermatophytes and 19 non-dermatophytes). PCR was positive in 77 (72%) specimens (63 T. rubrum and 14 pan-dermatophyte). A total of 37 specimens (35%) were positive for both fungal culture and PCR. PCR detected dermatophytes in 39 specimens that were missed by the fungal culture, increasing the diagnosis of dermatophyte-positive specimens by 37%. Five dermatophyte-culture-positive specimens were negative for PCR. This study demonstrates that PCR increases the sensitivity of detection of dermatophytes in nail specimens. Despite its limitations, the use of PCR can complement direct microscopic examination and fungal cultures to aid clinicians in the diagnosis of suspected dermatophytic onychomycosis.