Direct examination, histopathology and fungal culture for the diagnosis of onychomycosis: a retrospective, comparative study on 2245 specimens.

BACKGROUND Onychomycosis affects 5.5% of the general population and represents up to 50% of all nail diseases. Diagnosis and pathogen identification are essential in order to plan an adequate treatment. Many diagnostic techniques are available, however, no solid data regarding comparison between different techniques over a large number of specimens are available to date. OBJECTIVES To compare sensitivity and specificity of direct examination, histopathology and fungal culture in our referral mycology laboratory. METHODS Nail specimens received at the cutaneous pathology and mycology laboratory of the University Hospital Saint-Pierre (Brussels, Belgium) between January 1st and May 15th , 2018 were retrospectively analyzed. All specimens were submitted to direct examination and culture. In cases of adequate specimen size, histopathology was performed. Fungal culture was considered the gold standard for diagnosis. RESULTS A total of 2245 nail samples were included in the study. Onychomycosis was diagnosed in 1266 specimens. Sensitivity and positive predictive value were found to be higher for direct examination compared to histopathology, while sensitivity of direct examination was found to be lower. Combined approach with all the three techniques showed the highest rate of positivity, followed by the association of direct examination and histopathology. CONCLUSIONS To our knowledge, this study included the largest number of nail specimens to date, allowing a comparison between direct examination, culture and histopathology. Direct examination showed to be the most performing technique in routine practice. Histopathology represents the most effective option in cases where both specimen size and laboratory resources are adequate. Our paper adds to the literature the "real-life" experience of the mycology laboratory of a referral center for nail diseases.