Subtypes of Onychomycosis

Onychomycosis is divided into clinical subtypes based on the cause and progress of the infection.

• Distal lateral subungual onychomycosis (DLSO) is the most common form of onychomycosis. In DLSO, the fungus generally spreads from the skin and invades the underside of the nail where the nail meets the nail bed. Inflammation in these areas of the nail causes the symptoms of DLSO (see Symptoms).



• White superficial onychomycosis (WSO) is a rare infection caused by the fungi directly invading the surface of the nail plate and secondarily infecting the nail bed.



• In proximal subungual onychomycosis (PSO), the least common subtype, the fungi invade the cuticle (the skin around the nail) and the nail fold and then penetrate the nail plate (fingernail or toenail).



• Like DLSO, in endonyx onychomycosis (EO), the fungi reach the nail via the skin. Instead of infecting the nail bed, however, the fungi immediately invade the nail plate.



• Onychomycosis related to candidal (yeast) infection is a little different from onychomycosis related to other fungal infections. Candidal onychomycosis has several characteristics:
  
  
  • Onycholysis describes the nail separating from the nail bed. The separation is primarily caused by yeast called Candida.
  
  
  
  • Chronic mucocutaneous disease (disease of mucous membrane and regular skin) involves the nail plate (fingernail or toenail) and eventually the nail fold (the skin fold behind the cuticle, where the nail meets the finger or toe).
     
• Total dystrophic onychomycosis is not a distinct subtype of onychomycosis. Dystrophic onychomycosis is the term used to describe the most advanced form of any of the above subtypes, and it involves the entire nail unit. Dystrophic onychomycosis may cause permanent scarring of the nail matrix.