Performance of mycology and histopathology tests for the diagnosis of toenail onychomycosis due to filamentous fungi: Dermatophyte and non‐dermatophyte moulds

Abstract

Improvement of laboratory diagnosis of onychomychosis is important so that adequate treatment can be safely implemented. To evaluate and compare the performance of mycological and histopathological examinations in onychomycoses caused by dermatophyte and non-dermatophyte moulds. Patients with lateral/distal subungual onychomycosis in at least one hallux were enrolled in the protocol and assessed via mycological and histopathological tests. The isolation of filamentous fungi was considered the gold standard. Test performance was evaluated through sensitivity, specificity and positive and negative predictive values. A total of 212 patients were enrolled in the study. Direct microscopy (DM) was positive in 57.5% patients, and cultures in 34.4%. Among these patients, 23.3% were positive for dermatophytes, with Trichophyton rubrum the most frequently isolated, and 86.3% were positive for non-dermatophytes, with Neoscytalidium dimidiatum predominance. Histopathology was positive in 41.0% samples. Direct microscopy showed better sensitivity for non-dermatophyte moulds (P=.000) and nail clipping was more specific for dermatophyte (P=.018). Histopathology of the distal nail plate is a valuable complementary tool for the diagnosis of onychomycosis caused by dermatophytes and direct microscopy is especially useful for non-dermatophyte molds.

PAS and GMS utility in dermatopathology: Review of the current medical literature

“…17 Of note, this study was one of the few studies reviewed that found KOH and direct microscopy to be more sensitive than PAS and/or GMS, detecting an additional 40 positive cases, including non-dermatophyte pathogenic molds. 17 In contrast, Karaman et al found that GMS detected more than twice the number of onychomycosis cases than PAS (70 by GMS and 32 by PAS). By a latent class analysis, GMS was determined to have both high sensitivity and specificity, and it was recommended that GMS be used as a confirmatory test after screening with KOH and direct microscopy.…”

“…Due at least in part to the differences in study design, the prevalence of PAS and/or GMS positivity showed considerable variability. Supporting Information Table S1 [5][6][7][8][9][10][11][12][13][14][15][16][17] outlines all of the studies regarding onychomycosis detection methods and their findings.…”

“…11 No studies were designed to correlate specific histopathologic features with PAS or GMS positivity; however, one study noted a significant correlation between a positive PAS or GMS stain and the presence of neutrophils within the nail plate. 17 The first study to describe the utility of PAS staining for confirmation of onychomycosis described preferential zones of the nail involved by infection with specific dermatophyte species and saprophytic fungi. 16 In summary, the majority of the literature suggests that PAS is highly sensitive as an ancillary test for onychomycosis.…”

Diagnostic values of KOH examination, histological examination, and culture for onychomycosis: a latent class analysis

“…A recently published meta‐analysis has evaluated the utility of direct microscopic examination, culture, and histological examination for the diagnosis of onychomycosis . In the included studies of this meta‐analysis and similar studies, the positivity rates of these diagnostic methods have shown wide ranges (Table ). This rate was ranged from 23 to 77% for KOH, from 10 to 68% for culture, and from 38 to 80% for PAS.…”

“…Even in the most recent years, comparative studies have still been done to evaluate the value of these methods in the diagnosis of onychomycosis . However, there is no real gold standard to calculate their sensitivities and specificities.…”