Pityriasis versicolor and Pityrosporum ovale. Morphogenetic and ultrastructural considerations

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been performed on skin material of patients with pityriasis versicolor who were orally treated with itraconazole. Before as well as after therapy, variously sized spherical structures were observed on the surface of the keratinocytes with SEM. TEM examination revealed Pityrosporum ovale, predominantly in its mycelial phase, inside keratinocytes. The spherules as observed by SEM appeared to be amorphous, lipid-like droplets originating from the inside of the keratinocytes. The cytoplasm of the keratinocytes was at least partly occupied by the same amorphous material. It is therefore suggested that P. ovale penetrates the keratinocyte where degradation of the normal keratinous content to amorphous material takes place. This newly formed lipidic substrate may be an essential nutritive factor. The lipidified state of the stratum corneum persisted for at least 3 weeks after eradication of the fungus by itraconazole. It is speculated that the presence of large quantities of this lipid-like material might be the cause of hypopigmentation because it may constitute an ultraviolet light block.