(1) Fungal infection of the nails. Fungal infections can involve either the toenails or the fingernails. Nail fungal infection is usually caused by the dermatophyte fungi Trichophyton rubrum which can invade the nail bed. See dermatophytic onychomycosis.
Proximal white subungual onychomycosis: The rarest form of fungus infection of the finger or toenail. (Fungus infection of the finger or toenail is also called onychomycosis.) The infection begins in the nail fold (the portion of the nail opposite the tip of the finger).
Proximal white subungual onychomycosis is typically associated with HIV infection (AIDS), though it can follow injury to the nail.
The most common fungus causing the infection is called Trichophyton rubrum. Other causes include T. megninii, T. tonsiurans, T. mentagrophytes, T. schoenleinii, and Epidermophyton floccosum.
Proximal white subungual onychomycosis is diagnosed based upon its unusual location (in the portion of the nailbed closest to the hand). The diagnosis is confirmed by seeing the fungus under a microscope from a scraping of the tissue.
Proximal white subungual onychomycosis is treated by antifungal medications taken by mouth. Examples include itraconzole (SPORANOX) and terbinafine (LAMISIL).