Ustekinumab in BEhçet's Syndrome STudy

This non-interventional study is an observational and comparative cohort aiming to describe the success of biosimilar of ustekinumab in Behçet's syndrome in whom conventional approaches have failed or are not suitable well tolerated. Data on 208 patients is expected to be identified as follows: * data of 104 patients will be collected from patients who have received the ustekinumab * data of 104 patients will be collected from patients who have received the apremilast. Ustekinumab is usually prescribed subcutaneously at 90 mg on Week 0, 4, 12 and 20 within the standard of care. Following non-opposition to participate, patients data will be collected retrospectively according to local clinical practices and usual care, which usually comprises 3-month interval medical visits, except for the first month of treatment, in which the short-term tolerance of treatments is usually assessed (ie, baseline visit, then week 4, 12, 24, 36 and 52). Available data on clinical examination, biological tests and relevant clinical scores (BDCAF, BSAS and PhGA) that are performed within routine care will be retrieved. No changes to patients' usual care will be made (no additional visits, additional examinations or questionnaires), their safety and well-being remaining therefore unchanged. Data will be collected from the participant's medical record (containing medical reports and examinations, biological tests, nursing records, etc.), for the period of participation in the research, with the only purpose of meeting the objectives of the research. Data will be collected using an electronic eCRF observation book on the REDCap platform. The following data will be collected: demographic data (age, sex, weight, height); clinical data (history of the disease, pathology diagnosed, activity of the pathology), treatments, biological data, adverse events. No genetic data will be collected as part of the study. No data will be transferred abroad. No additional questionnaires, examinations or visits will be added by the research. Activity indexes for BS are usually calculated as part of routine care. The number, duration and intensity of oral ulcers of patients might be verified by the nurse or the site investigator according to the routine care. Patients data with active mucocutaneous Behçet's manifestations with an indication of starting apremilast within standard of care will be also retrospectively collected in order to establish a comparative group, using the same parameters above mentioned