Do Malassezia species play a role in exacerbation of scalp psoriasis?

Introduction. - Clinical expression of psoriasis is in part dependent on external factors, such as drugs, microorganisms or stress. However convincing evidence of the role of Malassezia species in the pathogenesis of the psoriasis is still lacking. Patients and methods. - Samples taken from scalp skin of 40 psoriatic patients and the same number of healthy individuals were observed under direct microsocopic examination and cultured on modified Dixon agar. Results. - Direct microscopy examination of psoriatic scalp scales was positive in 30 (75%) patients; while it was positive in only 12 (30%) healthy subjects (P = 0.003). Half of the cultures from healthy subjects showed no growth of colonies, but only 8 (15%) of psoriatic patients were negative. When an exacerbation has occurred in the previous weeks, pseudohyphaes were observed in 12 (40%) patients, Malassezia globosa was isolated in 18 (45%) patients and Malassezia restricta was isolated in 12 (30%) patients. In the group of patients having stable lesion, without any exacerbation in the previous weeks, no pseudohypahes were observed, M. globosa was not isolated, M. restricta was isolated in 4 (10%), and cultures were negative in 6 of them (15%). Conclusions. - Malassezia species form an integral part of normal cutaneous microflora in humans, however we found that during the episodes of exacerbation of the disease the presence of these yeasts, and particularly M. globosa, was increased. (C) 2013 Elsevier Masson SAS. All rights reserved.