Abstract
Onychomycosis is the most prevalent nail infection. Although it is not a life-threatening condition, it impacts the quality of life for many patients and often imposes a challenging diagnostic problem. The causative agents are dermatophytes, yeasts and non-dermatophytic moulds. Accurate and early diagnosis, including the identification of the causative species, is the key factor for rational therapy. Still, early diagnosis is not optimal as the current gold standard for the differentiation of the infectious agents is culture-based approaches. On the other hand, noninvasive optical technologies may enable differential diagnosis of nail pathologies including onychomycosis. When light penetrates and propagates along the nail tissue, it interacts in different ways with the components of either infected or healthy nail segments, providing a wealth of diagnostic information upon escaping the tissue. This review aims to assess alternative optical techniques for the rapid diagnosis of onychomycosis with a potential to monitor therapeutic response or even identify the fungal agent non-invasively and in real time in a clinical setting.
Highlights
Onychomycosis is a common, chronic, highly-relapsing fungal nail infection that affects primarily the toenails [1]
Subsequent classification of the Raman spectroscopy (RS) spectra test set, using the soft independent modeling of class analogy (SIMCA) method, yielded 92.8% accuracy in discriminating between the three classes and 100% accuracy in classifying healthy vs onychomycotic nails. These findings indicate that species-specific differences in fungal invasion mechanisms might trigger diverse chemical alterations of the nail plate, which can be reflected in the acquired Raman spectra and could be explored to differentiate among the culprit species of onychomycosis at patient-level in vivo
50 patients with suspected onychomycosis examined 58 patients with clinical suspicion of distal and lateral subungual onychomycosis covering and 10 controls were cross-examined with confocal laser scanning microscopy (CLSM) in comparison to three reference techniques (PCR, 10–75% of the surface of at least one great toenail by reflectance confocal microscopy (RCM)
Summary
Onychomycosis is a common, chronic, highly-relapsing fungal nail infection that affects primarily the toenails [1]. Histological investigation of nail plate samples after PAS staining is an alternative microscopic approach to the diagnosis of onychomycosis These methods are less effective in identifying the culprit fungal pathogen at species level. Optical techniques play a central role in modern clinical diagnostics and optical instrumentations or prototypes are currently being used or tested in clinical settings to assess health conditions and treatment outcomes Their main advantage is that they allow real-time visualization of tissues at high spatial resolution, being minimally or non-invasive, and optionally portable. The evidence from the application of three imaging and spectroscopic modalities, namely optical coherence tomography (OCT), confocal laser scanning microscopy (CLSM), and Raman spectroscopy (RS) for the evaluation of onychomycosis, is presented While they have not been established as reference methods, these techniques offer several advantages, being rapid, non-destructive, non-invasive and with the capacity for in vivo application
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