Polymerase chain reaction in the diagnosis of onychomycosis: a large,single‐institute study

Summary Background  Tests commonly used in the diagnosis of onychomycosis include potassium hydroxide (KOH) preparation, histopathological examination with periodic acid–Schiff stain (PAS) and culture. These tests are either time‐consuming or require specially trained personnel. A recently developed polymerase chain reaction (PCR) assay has the potential to provide a quick, inexpensive, operator‐independent diagnosis of onychomycosis. Objective  To determine the range of fungal species detected by the PCR technique and to compare this technique with KOH, PAS and culture on patient specimens. Methods  A total of 176 dermatophytic and nondermatophytic fungal culture isolates were tested by PCR. Five hundred and fifty nail specimens from 550 patients with suspected onychomycosis were split and tested concurrently with PCR, PAS, KOH and culture. Results  PCR was positive in 65 out of 66 dermatophyte culture isolates and negative in all 110 nondermatophyte and yeast isolates. Overall, PAS, PCR, KOH and culture were positive in 54%, 37%, 40% and 22% of specimens, respectively. Fifty‐two per cent were positive for KOH and PCR. Conclusion  PCR is a specific, relatively sensitive test for onychomycosis. When used in conjunction with KOH, PCR can produce positivity rates similar to those with PAS alone.