New diagnostic techniques

To review current diagnostic strategies. To review alternative diagnostic techniques.

The pathogen(s) responsible for onychomycosis must be identified to optimize treatment. Mycological examination is currently the most common diagnostic technique. This typically involves clearing with potassium hydroxide followed by microscopy. This direct test rapidly differentiates between living and dead hyphae. Sensitivity can be enhanced by using dimethyl sulfoxide (DMSO) or stains such as Chlorazol Black E. However, microscopy must always be combined with culture, allowing correct species identification. Accurate diagnosis depends on the expertise of laboratory staff and biologists and on the quality of the nail sample: samples should always be taken from the most proximal infected area. In the absence of experienced mycological laboratories, new laboratory techniques have been developed. Histological analysis by nail plate clipping has been shown to be an easy and efficient method for diagnosis. However, nail clipping is not an optimal technique for fungal culture and a large proportion of nonpathogenic but contaminant moulds can grow on culture medium. Moreover, histological analysis provides no information about causal agent or vitality. In vivo confocal microscopy and flow cytometry are powerful but complicated and costly techniques, making them unsuitable for routine use. Finally, polymerase chain reaction (PCR) (low proportion of positive results) and PCR-restriction fragment length polymorphism (PCR-RFLP) (suitable even for patients receiving antifungals) techniques have been developed. These molecular methods are cost-intensive and require highly skilled staff, meaning they are reserved exclusively for laboratories that process numerous nail samples.

In conclusion, mycological examination remains the gold standard technique; it provides the most information, at a reasonable cost with little inconvenience to the patient.