[Psoriasis. Pathogenesis]

A MULTIFACTORIAL ORIGIN: Psoriasis is an inflammatory dermatosis resulting from abnormal epidermal homeostatis and characterized by hyperproliferation and abnormal keratinocyte differentiation as well as activation of the skinis immune system. This dermatosis is a prototype of multifactorial conditions implicating hereditary and environmental pathogenic mechanisms. TWO TYPES OF PSORISASIS: Familial psoriasis is observed early in life and is strongly associated with the major histocompatibility complex, particularly CW6, DR7, B1, and B57 molecules. The sporadic non-familial form develops later in life.

A large number of triggering or aggravating factors have been identified in subjects genetically predisposed to psoriasis. Bacterial (streptococci) and viral (HIV) infections have been studied in particular. DRUGS AND OTHER FACTORS: The aggravating role of certain drugs as well as stress, psychoaffective factors, alcoholism and smoking is well known. KERATOCYES OR IMMUNE SYSTEM: One of the most widely discussed theories proposes a keratinocytic origin. Epidermal keratinocytes would be activated by various stimuli, secondarily provoking their abnormal proliferation and differentiation leading to the inflammatory reaction. In any case, the most popular theory suggests that psoriasis is an autoimmune disease implicating T lymphocytes.