Pityriasis capitis et dermatite séborrhéique du cuir chevelu : rôle du laboratoire dans l'évaluation d'une implication fongique

Dandruff (also called pityriasis capitis) and seborrheic dermatitis are the two main clinical situations in which the biologist is expected to confirm a diagnosis of «yeast infection» from the scalp. The global prevalence of seborrheic dermatitis, more common in the elderly population, would be 2 to 3%, with a male predominance. Dandruff exceeds 50% of the general post-pubertal population and of mean age. Examination of the scalp under ultraviolet (Wood's lamp) highlights metabolic activity of the fungus, revealed by spots of various sizes, fluorescent greenish yellow (color «bronze»), but without fluorescence of the hair itself. Two species, Malassezia globosa and M. restricta, now seem more closely associated with these clinical forms. Biological examination will assess the level of involvement and the relative density of the fungus on the scalp. The sampling methods are essential to know and determine the quality of biological examination, which is based on direct examination well conducted.