Evaluation of PCR for the diagnosis of dermatophytes in nail specimens from patients with suspected onychomycosis.

BACKGROUND

Conventional methods for detecting fungi in nail specimens are either nonspecific (microscopy) or insensitive (culture). Recently, PCR has been used to improve sensitivity in detecting the causative fungi in nail specimens from patients with suspected onychomycosis.

AIM: To compare the detection rates of PCR with those of microscopy (with potassium hydroxide; KOH) and culture for dermatophytes in nail specimens from patients with suspected onychomycosis.

METHODS

In total, 120 patients with clinically suspected onychomycosis were recruited, and using a topoisomerase II-based PCR, we compared the detection rate of dermatophytes for the three methods.

RESULTS

KOH microscopy, culture and PCR respectively yielded positive rates of 35 (29.2%), 12 (10%) and 48 (40%), and negative rates of 85 (70.8%), 108 (90%) and 72 (60%). Two culture-positive specimens were not detected by PCR, but PCR picked up 38 specimens missed by culture. Of the 35 specimens that were microscopy-positive, 12 grew dermatophytes and 23 nondermatophytes.

CONCLUSIONS

This study demonstrates that PCR has a higher positive and lower negative rate for detection of dermatophytes compared with KOH microscopy or culture. We suggest that PCR should be used as a complementary method for confirmation of clinically suspected dermatophytic onychomycosis.