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

Inclusion Criteria: * 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. Exclusion Criteria: * 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.