Design In this prospective cohort study disease activity prior to and after (14-16 weeks) initiation of anti-TNF treatment will be assessed. The endpoint is the treatment outcome defined as A: Responder according to the specific criteria described below (incl. drug-continuation) or B: Non-responder (incl. drug-discontinuation due to unacceptable side effects). Whether a patient will discontinue therapy is assumed to be based on a certain degree of shared decision making between the patient and physician supported by principles from national guidelines for each CID as recommended in the respective national guidelines and laboratory data.