[Psoriasis: evolution and revolution].

Psoriasis is a model disease in dermatology. It is a common disease that affects at least 2 to 3 % of the population. It is an illness characterized by an excessive reaction of the skin, in term of proinflammatory cytokines release, to no specific attacks: these attacks can be immunological, mechanical, metabolic, drug-induced or psychological. This excessive reaction is characterized by epidermal proliferation combined with incomplete terminal differentiation, as well as an inflammatory response responsible for the chronic nature of the lesions. The way to understand psoriasis is therefore to reach a better appreciation of the messages that enable the skin cells to initiate an inflammatory response, and by better understanding the way in which the inflammatory cells responsible for innate and acquired immune responses are capable of bringing about proliferation and abnormal epidermal differentiation. Taking an interest in psoriasis is therefore taking an interest in all facets of skin physiology and in all the ways the skin reacts to attacks from the environment. Every year for more than thirty years, more than 300 publications have endeavoured to explore one aspect or another of psoriasis from a clinical, epidemiological, physiopathological or therapeutic point of view. There is no new technique for observing the skin that has not been immediately applied to the study of psoriasis - which is privileged to enjoy the reflected progress made in dermatology. Nor has psoriasis remained untouched by whims of fashion, all manner of scenarios having been suggested to explain it, right from a scarring disease to an autoimmune illness through a genetic or psychosomatic disorder. Psoriasis is at the origin of a medical revolution mounted to supplement and enhance the effectiveness of evidence-based medicine ; it is the "patient-centred medicine". Psoriasis only exceptionally jeopardizes life. Conversely, it is a disease that does affect quality of life. The patient alone must be the judge of his or her quality of life, and it is therefore up to the patient, not the doctor, to gauge the severity of psoriasis and hence decide on reasonable therapeutic indications. Psoriasis, then, cannot be treated without placing the patient, not the illness, at the centre of therapeutic negotiations. The 20th century has seen the disease targeted by boundless efforts ; the 21st century will see the development of medical techniques that allow the patient, in all its complexity, to be positioned at the centre of therapeutic efforts. This revolution began in dermatology, centring around psoriasis, and is spreading progressively to all chronic disorders and all disciplines. New quite interesting therapeutic weapons are available from a few months making possible to better adjust the therapeutic strategies of psoriasis to the patients needs but they are expensive opening again the debates on the limit of the social solidarity.