A comprehensive review of nondermatophyte mould onychomycosis: Epidemiology, diagnosis and management

Abstract

Nondermatophyte moulds (NDMs) are widely distributed and can be detected in association with mycotic nails; however, sometimes it can be challenging to establish the role of NDMs in the pathogenesis of onychomycosis (i.e. causative vs. contaminant). In studies where the ongoing invasive presence of NDMs is confirmed through repeat cultures, the global prevalence of NDMs in onychomycosis patients is estimated at 6.9% with the 3 most common genus being: Aspergillus, Scopulariopsis and Fusarium. NDM onychomycosis can, in many cases, appear clinically indistinguishable from dermatophyte onychomycosis. Clinical features suggestive of NDMs include proximal subungual onychomycosis with paronychia associated with Aspergillus spp., Fusarium spp. and Scopulariopsis brevicaulis, as well as superficial white onychomycosis in a deep and diffused pattern associated with Aspergillus and Fusarium. Longitudinal streaks seen in patients with distal and lateral onychomycosis may serve as an additional indicator. For diagnosis, light microscopic examination should demonstrate fungal filaments consistent with an NDM with at least two independent isolations in the absence of a dermatophyte; the advent of molecular testing combined with histological assessment may serve as an alternative with improved sensitivity and turnover time. In most instances, antifungal susceptibility testing has limited value. Information on effective treatments for NDM onychomycosis is relatively scarce, unlike the situation in the study of dermatophyte onychomycosis. Terbinafine and itraconazole therapy (continuous and pulsed) appear effective to varying extents for treating onychomycosis caused by Aspergillus, Fusarium or Scopulariopsis. There is scant literature on oral treatments for Neoscytalidium.

Global prevalence of onychomycosis in general and special populations: An updated perspective

“…In the absence of repeat sampling, we observed NDM detection results that were highly variable in clinically suspected patients (Range; Global North: 0%–49.1%, Global South: 1.2%–20%), as opposed to studies where repeat sampling is performed (Range; Global North: 0%–4.7%, Global South: 0%–9%); based on results from the Global North regions, the NDM detection rate per single sampling was significantly higher than the rate per repeat sampling. This reinforces the current recommendation that the diagnosis of NDM onychomycosis is often ambiguous that requires confirmation from a second sample or from a combined histopathologic examination 123,124 …”