The main objective of the study is to evaluate the additional effect of a narrow band Type B
Ultraviolet (UVB) therapy on the treatment of severe plaque psoriasis with fumaric acid
esters (FAE) in comparison to FAE monotherapy. The secondary objectives are to evaluate the
effect of an additional narrow band UVB therapy on the cumulative FAE dose required to reach
Psoriasis Area and Severity Index (PASI) 75 in comparison to FAE monotherapy and to evaluate
whether a leukopenia and lymphopenia frequently occurring during the FAE treatment is a
positive predictive factor for the treatment response.