In all non-AS forms of SpA changes somewhat similar to those of AS can occur, especially in patients with the tissue type HLA-B27. However, other features may also occur, especially in psoriatic and reactive arthritis. Sacroiliitis in these disorders may be unilateral and the spinal changes can be characterized by more voluminous new bone formation (non-marginal syndesmophytes or para-syndesmophytes) than seen in AS. (doi:10.1136/ARD.57.3.135) accompanied by signs of inflammation during active phases. Predominant osseous inflammation is occasionally seen as part of psoriatic arthritis, especially in patients with pustular psoriasis, where there can be concomitant osseous sclerosis. These changes can be similar to those associated with the skin disease pustulosis palmoplantaris.