Histopathological examination of nail clippings using PAS staining (HPE‐PAS): gold standard in diagnosis of Onychomycosis

Abstract

Onychomycosis is fungal infection of one or more of the nail units. However, because fungi cause only about half of all nail dystrophies, the use of appropriate diagnostic techniques is important to ensure correct diagnosis and treatment. Aim of the present study was to compare direct microscopy, culture and HPE-PAS for diagnosis of onychomycosis by evaluating their sensitivity and various other relevant statistical parameters. A prospective, hospital-based, cross-sectional study was conducted on 216 patients with a high degree of clinical suspicion of onychomycosis. Nail specimens were evaluated using three diagnostic methods, i.e. direct microscopy using 20% Potassium hydroxide (KOH) & 40% Di-methyl-suphoxide (DMSO), culture and histopathological examination using PAS stain (HPE-PAS). Of 216 patients direct microscopy was positive in 138 (63.9%), culture in 147 (68%) and HPE-PAS in 164 patients (76%). One hundred and seventy-nine patients fitted into the criteria set for confirmed diagnosis of onychomycosis. Using this as a denominator; direct microscopy, culture and HPE-PAS had sensitivities of 77.1%, 70% and 91.6% respectively. Also, HPE-PAS showed the highest sensitivity of 94.7% in 19 cases with prediagnostic antimycotic treatment compared to direct microscopy (42.1%) or culture (57.9%). HPE-PAS shows high sensitivity for diagnosis of onychomycosis and can be considered as a gold standard in the diagnosis of onychomycosis.

A practical application of onychomycosis cure – combining patient, physician and regulatory body perspectives

“…Obtaining mycological cure is supported by regulatory bodies, which define mycological cure in the context of clinical trials, as a negative stain and a negative culture . Sensitivity of mycological testing can range from 54% (culture) to 88% (PAS) and can be enhanced if used in combination (KOH + culture 89% vs KOH alone 64%) . Sensitivity should not be the only factor to consider when choosing a mycological test.…”

“…Sensitivity should not be the only factor to consider when choosing a mycological test. For instance, PAS is more sensitive than culture but culture assays can supply more information . Additionally, false negatives are an inherent risk with mycological testing, potentially attributed to the presence of partially‐treated strains and selectivity agents .…”

“…44 Sensitivity of mycological testing can range from 54% (culture) to 88% (PAS) and can be enhanced if used in combination (KOH + culture 89% vs KOH alone 64%). 45,46 Sensitivity should not be the only factor to consider when choosing a mycological test. For instance, PAS is more sensitive than culture but culture assays can supply more information.…”

Liquid chromatography–tandem mass spectrometry is effective for analysis of ergosterol in fungal‐infected nails

“…In this test, 20% KOH is added to ground‐up nail samples on a slide and incubated for 30 min, then the slide is examined under microscopy for the presence of hyphae; however, this procedure can yield false negatives . Periodic acid–Schiff staining for mycelium or fungal culture (FC) may be performed, but the long incubation process for culture makes it easily contaminated, affecting the authenticity of the result . DNA detection has a number of advantages in testing, but owing to its specificity, specific primers are needed for different species.…”

“…6 Periodic acid-Schiff staining for mycelium or fungal culture (FC) may be performed, but the long incubation process for culture makes it easily contaminated, affecting the authenticity of the result. 7 DNA detection has a number of advantages in testing, but owing to its specificity, specific primers are needed for different species. Some obscure or hidden fungal manifestations can appear in nononychomycosis conditions such as onycholysis, psoriatic nail or onychomadesis.…”