Proximal subungual onychomycosis is typically caused by Trichophyton rubrum, a dermatophyte. The diagnosis of this condition should prompt HIV testing in a previously healthy individual. The diagnosis of proximal subungual onychomycosis may be made in several ways. This is especially true of superficial white onychomycosis, which is not necessarily associated with the immunocompromised state. Potassium hydroxide preparation of the subungual debris may reveal hyphae.
Fungal culture is often confirmatory.
Finally, a nail clipping or biopsy may be performed and sent for pathological processing, with a PAS stain to reveal any fungal forms. Treatment of proximal subungual onychomycosis is successful only with systemic antifungal therapy. Topical therapies are ineffective for fungal nail infections. Itraconazole 200 mg daily for 12 weeks is often effective. A pulse dosing regimen is used by some dermatologists.