Occurrence of Pityrosporum Ovale/orbiculare in Seborrheic Keratosis and Melanocytic Naevus

Bioptic specimens from 224 melanocytic naevus lesions and 121 seborrheic keratosis lesions were stained with hematoxylin-eosin and examined under the light microscope. Pityrosporum ovale/orbiculare (Malassezia furfur) was found in 35% of melanocytic naevi and in 36% of seborrheic keratoses. The finding of Pityrosporum ovale/orbiculare was confirmed by PAS (periodic acid shift), methenamide silver staining and electron microscopy. The presence, number and location of Pityrosporum ovale/orbiculare microorganisms, the presence and degree of papillomatosis, the presence and degree of hyperkeratosis, lesion diameters and patients’age were recorded. The relation of papillomatosis presence to the finding of Pityrosporum ovale/orbiculare in melanocytic naevus and seborrheic keratosis was found. In 29 % of melanocytic naevi and 59 % of seborrheic keratoses, papillomatosis was present but not Pityrosporum ovale/orbiculare while, in 54 % of melanocytic naevi and 81 % of seborrheic keratoses, both papillomatosis and Pityrosporum ovale/orbiculare were demonstrated.