Onicomicosis: comparación de tres métodos diagnósticos en pacientes del Archipiélago Juan Fernández

Abstract

BackgroundOnychomycosis is a prevalent disease in the general population. There are currently 2 methods recommended for its clinical and laboratory diagnosis, direct microscopy (with potassium hydroxide KOH) and mycology culture. However, both test have notable deficiencies that call into question its clinical efficacy. Direct microscopy has a low sensitivity and is operator dependent, while the mycology culture is very sensitive and requires an incubation period of 35 days. Consequently, numerous techniques have been employed to overcome the diagnostic difficulties in onychomycosis. These include the histological study of the nail plate with PAS staining. This has shown good diagnostic indices, with reports of positivity of 33 to 92%, with a mean of 48%. ObjectiveTo determine and compare the sensitivity and negative predictive value of three diagnostic methods for onychomycosis: Direct mycological with potassium hydroxide, mycological culture, and biopsy of nail plate with PAS staining in patients with clinical suspicion of onychomycosis in residents of the Juan Fernández Archipelago. Materials and methodsA cross-sectional study was conducted with a sample size of 55 patients living in the Juan Fernandez Archipelago. Specimens of nail tissue were taken for the direct mycological study, mycological culture, and histological study with PAS staining. Calculation and comparison of sensitivity and NPV for the three diagnostic methods was performed. ResultsA total of 39 (70.9%) patients showed positive in at least one of the three practiced methods used, which was considered positive for onychomycosis (gold standard). By comparing each test in isolation, the best sensitivity was direct microscopy with 83%, followed by PAS (80.9%), and finally culture (46.8%). The highest sensitivity (97.9%) was detected in the combination of direct microscopy with potassium hydroxide and with histology PAS staining. The negative predictive value was 50% for direct microscopy, 47.1% for PAS, and 24.2% for the culture. ConclusionsThe high sensitivity demonstrated and high negative predictive value shown in the histopathological PAS technique can be considered a simple and rapid alternative method for the diagnosis of onychomycosis.