Efficacy Study on Dimethyl Fumarate to Treat Moderate to Severe Plaque Psoriasis

Inclusion Criteria: * adult patients, \>=18 years of age; * clinical diagnosis of stable moderate to severe plaque psoriasis for at least 6 months; * clinical diagnosis of plaque psoriasis with an affected body surface area of no less than 10% and least 10 on the PASI scale and on the sPGA score at least as moderate; * Besides psoriasis, patient is in good general health * Patients with a DLQI score of at least 10 Exclusion Criteria: * Pustular forms of psoriasis, erythrodermic or guttate psoriasis; * Known immunosuppressive diseases; * Presence of another serious or progressive disease including skin malignancies; * Active skin disease; * Use of topical medical treatment or UVB treatment during the 2 weeks preceding randomization; * Use of systemic anti-psoriatic treatment preceding randomization: methotrexate, cyclosporine, steroids or PUVA (psoralen + UVA treatment) treatment within 4 weeks; biological treatment within 12 weeks; Stelara within 20 weeks; acitretin within 6 months; * Treatment with Fumaderm® or other Dimethyl Fumarate containing products within 12 weeks prior randomization; * Treatment with drugs influencing the course of psoriasis (e.g., antimalarial drugs, lithium) within 4 weeks prior to randomization; * Treatment with retinoids, other immunosuppressive treatment, cytostatics or drugs with known harmful effects on the kidneys within 3 months prior to randomization; * On-going stomach or intestinal problems; * Aspartate transaminase (AST), Alanine transaminase (ALT) \> 2 x upper normal limit (ULN), or Gamma-glutamyltransferase (γ-GT) \> 2.5 x ULN; * Creatinine Clearance \< 60 ml/min; * Leucopenia, eosinophilia or lymphopenia; * Protein in the urine test;