ROLL'YN-UST: an Observational Study in Patients Treated by Steqeyma®, an Ustekinumab Biosimilar

Who May Qualify: - Be an adult (18 years of age or older at the time of inclusion) followed in specialty care and diagnosed with of one of the following conditions: Crohn's disease, Plaque psoriasis - Treated for at least 6 months prior to inclusion with the reference Ustekinumab for the pathology in question: Crohn's disease, Plaque psoriasis - Stable for at least 3 months according to the prescribing physician and in clinical remission according to the specific disease activity score. - For whom the specialist has decided to switch to the biosimilar treatment developed and marketed by Celltrion on the day of inclusion (shared medical decision independent of the study) - Have an email address. - Have a mobile phone number. - Be able to understand and complete questionnaires in French. - Not opposed to participating in the study. - Be affiliated to a French Social Security scheme or be a beneficiary of such a scheme. Who Should NOT Join This Trial: - Patients under guardianship or otherwise deprived of their freedom. - Pregnant women or women of childbearing potential who wish to become pregnant while taking one of the study treatments. - Patients participating at the time of inclusion in a clinical trial or other clinical study that prohibits simultaneous participation in other studies. - Contraindication to study products. Always talk to your doctor about whether this trial is right for you.