Onychomycosis I: epidemiology and etiology

A common disease. Onychomycosis is one of the most common nail diseases. Di fficult to bear by some patients, onychomycosis is one of the most frequent reasons for consulting a mycological center. However, the estimated freque ncy of onychomycosis varies depending on whether the studies of prevalence concern the general population (2 to 13 % according to different authors) o r target individuals consulting a primary care physician. Recent large scal e surveys in Europe indicate a high prevalence in adults: 20 to 30 %, depen ding on whether the instigator is a general practitioner or a dermatologist . Epidemiological features. All studies concur that onychomycosis has been in constant progression over the last twenty years. Rarely observed in childr en, frequent in adults, onychomycosis principally affects the elderly. In W estern Europe and in North America, onychomycosis involves principally the feet, especially in men. By contrast, in Southern Europe, in the Middle and Far East, the prevalence is highest in women's fingernails (often associat ed with paronychia). Favoring factors. Among the factors promoting fungal n ail invasion, some are local patient-dependent factors (trophic disorders a nd circulatory impairment, overlapping of digits, etc.) and others are more general factors such as immunosuppression, diabetes mellitus or psoriasis. There are also behavioral factors (occupation, lifestyle, sports) which fa vor encounter with the pathogenic fungi. Causal species. Among the numerous species (nearly one hundred) responsible for onychomycosis, emphasis should be given to those which are keratinophi lic, i.e., dermatophytes (mainly the antropophilic types) such as Trichophy ton rubrum, and Trichophyton mentagrophytes, var. interdigitale, pseudo-der matophytes such as Scytalidium spp. and Onychocola canadensis, or geophilic saprophytes (molds) requiring stringent criteria (direct mycological or hi stological examination) to establish their; pathogenicity. A mold (Aspergil lus sp., Fusarium sp.) in a nail can be a dangerous portal of entry in immu nocompromised subjects. Among the yeasts that invade mainly the fingernails , besides commensal species (such as Candida albicans), other species behav e as predictive parasites of the nail (Candida ciferrii, Candida haemulonii ).