Significance of Polymerase Chain Reaction for the Detection of Causative Fungi of Onychomycosis: Comparison with Fungus Culture and KONCPA(KOH+Nail Clipping+ PAS(periodic acid-Schiff) stain)

Kwon, Oh Chan; Paik, Seung Churl; Cho, Baik Kee

Abstract

BACKGROUND: It has been known that the polymerase chain reaction(PCR) test of clinical specimens including blood, sputum, urine, and cerebrospinal fluid collected from patients with systemic fungal infection is a highly sensitive diagnostic method. Recently, the PCR test was applied to the diagnosis of onychomycosis.
OBJECTIVE
This study was aimed to explore whether the PCR test would be a more sensitive diagnostic tool than the KOH smear, fungus culture and KONCPA(KOH+Nail Clipping+ PAS(periodic acid-Schiff) stain) test in diagnosing the onychomycosis.
METHODS
Using 50 nail samples from 50 patients with onychomycosis, the result of the PCR test was compared with those of the KOH smear, fungus culture and KONCPA test.
RESULTS
The results were as follows: 1. The positive rates for detecting the causative fungi from the KOH smear, fungus culture, KONCPA test and PCR test were 64.0%, 46.0%, 90.0%, and 100.0% respectively. 2. The fungus culture identified the causative fungi from 23 samples, of which 21(91.2%) were T. rubrum, 1(4.4%) Candida sp. and 1(4.4%) C. albicans. KONCPA test yielded higher positivity by detecting the pathogenic fungi in 45 samples: dermatophytes 35(77.8%), mixed infections of dermatophytes and Candida sp. 6(13.3%), molds 2(4.4%) and unclassified 2(4.4%). The PCR test yielded the highest positivity by detecting the pathogenic fungi in all samples ; T. rubrum 44(88.0%) and unclassified 6(12.0%). 3. Compared with the results of fungus culture and KONCPA test, that of PCR test showed some differences. The case of Candida sp. in fungus culture was identified as T. rubrum in PCR ; the case of C. albicans in fungus culture as unclassified in the PCR. Five cases of mixed infection and 2 cases of mold infection in the KONCPA test were diagnosed as T. rubrum infection in the PCR test.
CONCLUSION
The PCR test is useful in diagnosing the onychomycosis because of its highest positive rate in detecting the causative fungi compared with fungus culture and the KONCPA test. Furthermore, a more accurate diagnostic method such as the PCR test will be necessary in case Candida sp. or mold is cultured from the infected nail specimen.