Infrared spectroscopy as a novel tool to diagnose onychomycosis.

Background: The determination of causative organisms of onychomycosis is still not optimal. There remains a need for a cheap, fast and easy-to-perform diagnostic tool with a high capacity to distinguish between organisms.
Objectives: To determine whether attenuated total-reflectance Fourier transform infrared (ATR-FTIR) spectroscopy can detect and differentiate causative agents in culture-based, ex vivo nail and in vivo nail models.
Methods: A methodological study was conducted. Both the ex vivo nail model and in vivo pilot study were carried out in an academic university hospital.
Results: Analysis of cultured fungi revealed spectral differences for dermatophytes (1692-1606 and 1044-1004 cm ^-1 ) and nondermatophytes and yeasts (973-937 cm ^-1 ), confirmed by dendrograms showing an excellent separation between samples from different genera or species. Exploration of dermatophytes, nondermatophytes and yeasts growing on ex vivo nails exposed prominent differences from 1200 to 900 cm ^-1 . Prediction models resulted in a 96·9% accurate classification of uninfected nails and nails infected with dermatophytes, nondermatophytes and yeasts. Overall correct classification rates of 91·0%, 97·7% and 98·6% were obtained for discrimination between dermatophyte, nondermatophyte and yeast genera or species, respectively. Spectra of in vivo infected and uninfected nails also revealed distinct spectral differences (3000-2811 cm ^-1 , 1043-950 cm ^-1 and 1676-1553 cm ^-1 ), illustrated by two main clusters (uninfected vs. infected) on a dendrogram.
Conclusions: Our data suggest that ATR-FTIR spectroscopy may be a promising, fast and accurate method to determine onychomycosis, including identification of the causative organism, bypassing the need for lengthy fungal cultures.
(© 2018 British Association of Dermatologists.)