[Clinical types of onychomycosis]

Clinical classification of onychomycosis is based on how the pathogenic agent penetrates the unguis. The disto-lateral sub-ungual variety is the most common. Dermatophytes (especially Trichophyton rubrum) and Scytalidium in tropical regions (Sc hyalium, Sc dimidiatum) are the most frequent toenail pathogens. Progression of a yellow friable sub-ungual hyperkeratosis associated with longitudinal striations and/or xanthonychial or leuconychial zones (sometimes pigmented with Trichophyton rubrum nigricans or Scopulariopsis brevicaulis) lead rapidly to onycholysis and later to total dystrophy of the ungual plate. Associated paronychia is more common in scytalidiasis. Candida species (tropicalis, parapsilosis) and fungi (Aspergillus sp. Fusarium sp, Acremonium sp, Penicillium sp, Scopulariopsis brevicaulis) generally colonize pre-existing onycholysis. For the fingernails, candidal colonizations secondary to pre-existing onycholysis is much more frequent than primary dermatophyte or scytalidium onychomycoses which are much less hyperkeratotic than on toenails. The one hand two feet tinea syndrome caused by Trichophyton rubrum is a particular entity. Proximal sub-ungual onychomycoses without fingernail or toenail paronychia is generally caused by Trichophyton rubrum in immunodepressed subjects (AIDS). Initial proximal leuconychia progresses to the distal part of the nail. Proximal lesions associating proximal leuconychia and paronychia result from fungi, Fusarium being the most commonly identified agent. Onyxis complicating chronic paronychia, generally related to Candida colonization, occurs in subjects with particular conditions (immunodepression, distal vascular disorders). Superficial onychomycosis, e.g. superficial toenail leuconychia, is mainly due to Trichophyton interdigitale, more exceptionally to Trichophyton rubrum (children, immunodepressed), and rarely Candida (children). Endonyx onychomycosis occurs when the pathogen invades the entire thickness of the nail (milky leuconychia without sub-ungual hyperkeratosis). Trichopnyton violaceum or soudanense is the most common pathogen. Even though the clinical presentation of onychomycosis is highly suggestive of the pathogenic agent, the lack of specific criteria implies a mycological sample to confirm the diagnosis and identify the causal agent before initiating treatment.