Patients with spondylarthritis (SpA) (including ankylosing spondylitis, psoriatic arthritis, arthritis as part of inflammatory bowel disease and reactive arthritis) have axial involvement (the spine) as well as peripheral inflammation in joints and entheses (where the tendons and ligaments are anchored to the bone). Patients with high disease activity of SpA may need biological treatment (anti-TNF alpha), which are very expensive medications. Thus it is necessary to have a sensitive method for assessing the response to treatment. Ultrasonography (US) is a validated and reliable method for assessing disease activity in joints and tendons, and may be used to follow the treatment response.||The present study will include patients with SpA starting on anti-TNF alpha treatment (as first biologic medication or when switching to a new biologic treatment). The study is an extension of the ongoing NORDMARD study (Norwegian longitudinal observational study of arthritic patients starting disease-modifying treatment). The patients will be examined by use of US of 38 joints and 14 entheses at baseline and after 3, 6 and 12 months.||The objectives are to explore US as a method to assess peripheral inflammatory activity for evaluation of response to medication as well as to compare the US pathology with clinical and laboratory findings.