C-219. Polymerase Chain Reaction (PCR) in the Diagnosis of Onychomycosis: Single Institute Study of 3097 Specimens

C. E. Litz, R. Z. Cavagnolo;
ProPath, Inc., Dallas, TX.

Background: Onychomycosis is a common disorder currently diagnosed by expensive, time consuming tests including: culture, potassium hydroxide (KOH) preparation, and/or periodic acid Schiff (PAS) stain of histologic sections of infected nail tissue. PCR based technology has been proposed as the basis of a better test. The purpose of this study is to compare the sensitivity and specificity of a recently developed PCR test with other commonly employed tests in the diagnosis of onychomycosis. Method: 3097 finger and toenail specimens from patients clinically suspected of having onychomycosis were analyzed by both PCR and PAS tests; 346 and 196 of these were also examined by culture and KOH, respectively. The PCR test employs an inexpensive alkaline/freeze/thaw extraction procedure. This is followed by PCR amplification employing dermatophyte-specific primers to the Chitin Synthase 1 gene (CHS1) and agarose gel electrophoresis. Amplimers detected at 407bp indicate the presence of dermatophyte DNA. Culture, KOH and PAS tests were performed using standard methodology by experienced personnel. Results: 1733 (56%) and 855 (28%) specimens were PAS and PCR positive, respectively. 780 (25%) were both PAS and PCR positive. 35 of 86 KOH positive cases and 50 of 72 culture positive cases were PCR positive. Sensitivity of the PCR test compared to PAS, culture, and KOH tests was 45%, 69%, and 41%, respectively. 953 of 1038 PAS negative cases, 102 of 110 KOH negative cases, 236 of 274 culture negative cases were PCR negative. Specificity of the PCR test to PAS, culture, and KOH tests was 92%, 86%, and 93%, respectively. Conclusion: The PCR test is a specific test with moderate sensitivity in the diagnosis of onychomycosis. When PCR is used as an initial test in the diagnosis of onychomycosis followed by more expensive PAS testing in PCR negative cases, it has the potential to reduce the number of PAS tests without reducing sensitivity.