There is limited knowledge about radiographic changes. Findings by MRI have not been systematically analysed and can vary considerably depending on type, stage and activity of disease. In all non-AS forms of SpA changes to some degree similar to those of AS may occur, especially in patients with tissue type HLA B27. However, some features are characteristic of the other forms of SpA. This is particularly the case in psoriatic and reactive arthritis. Sacroiliitis in these disorders is often unilateral and the spinal changes can be characterised by more voluminous new bone formation (para-syndesmophytes) than seen in AS with signs of inflammation during active phases. In psoriatic arthropathy predominant osseous inflammation can be seen. This is particularly seen in changes associated with pustular psoriasis, which can be similar to those associated with the skin disease pustulosis palmoplantaris.