Comparison of Fungus Culture with Histopathologic Examination in Onychomycosis

Kim, Sung Wook; Cho, Baik Kee

Abstract

BACKGROUND: Onychomycosis is one of the most common nail disorders, but dermatologists have experienced poor efficacy ol therapy because of incorrect diagnosis. It has been reported that histopathologic evaluation of the nail plate by nail clipping might be a useful supportive method for identification of causative fungi showing higher detection rates.
OBJECTIVE
This study was aimed to determine whether histopathologic examination support for identification of causative fungi and whether it increased. The diagnostic sensitivity of onychomycosis even in cases that those fungus culture fail to identify the causative fungi, and to clarify the relative frequency of causative fungi in onychomycosis.
METHODS
Histopathologic findings of 218 onychomycotic nail samples, proven by KOH smear, were analyzed and compared with the results of fungus culture.
RESULTS
The results were as follows; 1. Histopathologic examination showed higher positive rate (73.9%) than that of fungus culture (35.8%) in identifying the etiologic fungi. 2. The 3 groups of causative fungi confirmed by fungus culture showed morphologically distinguishable characteristics in histopathologic examination: Dermatophytes showed septated long, thin and regular hyphae with or without arthrospores, while Candida sp. showed blastospores, grape-like clusters of regular spores and pseudohyphae. Mold exhibited irregular hyphae with variable width and aggregates of irregular spores. Mixed infections showed the characteristic findings of the corresponding groups at the different sites of the nail samples. 3. Frequency of the causative fungi by fungus culture was 88.5% of dermatophytes, 5.1% of Candida sp. and 6.4% of mold. In histopathologic examination, the frequency was considered as 80.7% of dermatophytes,8.1% of Candida sp.,6.2% of mold and 1.9% of mixed infection. 4. In 42 of 59 samples of T. rubrum and 3 of 10 samples of T. mentagrophytes, hyphae were observed on the ventral and dorsal layer of the nail plate, respectively. In histopathologic sections, 88 of 130 samples of dermatophytes showed fungal element on the ventral layer of the nail plate and all 13 samples of Candida sp. on the subungal keratin layer and ventral layer of the nail plate.
CONCLUSION
Histopathologic examination in onychomycosis is considered to be simple, useful supportive method in studying the classification and distribution of causative fungi of onychomycosis and might be included in the routine laboratory tests for making the presumptive diagnosis of causative fungi of onychomycosis. Moreover, we can determine the site of involvement of the fungi in the nail, so we can get useful informations about mixed infections or contaminations