Role of onychoscopy in differentiation between distal subungual onychomycosis, psoriasis, and traumatic onycholysis

Background: Dermoscopy is helpful in the diagnosis of numerous nail diseases. Objective: To describe the specific dermoscopic signs for psoriasis, traumatic onycholysis, and distal subungual onychomycosis. Patients and methods: The study was carried out on 39 patients with distal subungual onycholysis. Dermoscopic imaging and mycological examination (microscopic examination with 20% KOH and culture on Sabouraud’s dextrose agar) were carried out. The final mycological results were correlated with the detected dermoscopic features. Results: In mycologically positive patients, confirmed as positive by means of both microscopic examination and fungal culture, the most common and specific dermoscopic features were longitudinal striae and jagged edge with spikes of the proximal margin of the onycholytic nail. In mycologically negative traumatic onycholysis, the most common and unique feature was linear edge without spikes of the proximal margin of the onycholytic nail; however, in dermatophyte-negative psoriasis, the most specific feature was the erythematous border. Conclusion: Longitudinal striae and jagged edge with spikes patterns were distinctive dermoscopic signs, exclusive to distal subungual onychomycosis. Dermoscopy should be considered a helpful, quite simple, quick, and inexpensive technique for diagnosis and differentiation between distal subungual onychomycosis, psoriasis, and traumatic onycholysis.