Pathophysiological basis of systemic treatments in psoriasis.

Over the past 15 years, the spectrum of systemic antipsoriatic treatments has dramatically expanded. Until the end of the last millennium, systemic therapy had been restricted to four oral agents: methotrexate, cyclosporine, acitretin, and fumaric acid esters. Today, there are additionally seven biologics and one new oral antipsoriatic drug, as well as the first available biosimilars. Six more biologics with novel target structures and at least four biosimilars are currently being developed (phase III). This progress has been based on new insights into the pathogenesis of psoriasis, in which tumor necrosis factor and especially Th17 immune responses with their associated cytokines interleukin 23 and 17 play a key role. The development of new-generation biologics as well as immunomodulatory small molecules can be attributed to these pathophysiological findings. Phosphodiesterase 4 inhibitors, dimethyl fumarate, and Janus kinase inhibitors all interact with Th17 immune responses. Some of these drugs are in advanced clinical development and are also beneficial in psoriatic arthritis. Today, psoriasis and psoriatic arthritis therefore rank among the most readily treatable inflammatory autoimmune disorders. Dermatology is increasingly becoming a specialty of modern targeted immunotherapies.