The spondyloarthropathies (SpA) are a group of chronic autoimmune disorders of the joint.1 Entities belonging to this group are ankylosing spondylitis (AS), psoriatic arthritis (PsA), reactive arthritis, arthritis related to inflammatory bowel diseases such as Crohn's disease (CD) and ulcerative colitis, and arthritis associated with acute anterior uveitis. Patients who fulfil the European Spondyloarthropathy Study Group (ESSG) classification criteria,2 but who do not belong to one of the subtypes described above are termed undifferentiated spondyloarthropathy.3

This common rheumatic condition has a global prevalence of 0.5–1%, with, however, important racial and geographical differences and a clear male predominance. Juveniles as well as adults can be affected by one of the diseases included in the SpA group. All the diseases in this group have common clinical, radiological, and genetic features. The typical hallmarks of this disease group are sacroiliitis, spondylitis, peripheral arthritis, and enthesitis. The spondylitis typically affects the insertion of the collateral ligaments with syndesmophyte formation and the zygapophysial joints. The peripheral arthritis is asymmetrical and mainly affects the legs. The synovitis may be self limiting or chronic with joint destruction. Enthesitis, mostly localised at the Achilles tendon and plantar fascia is also typical for this disease entity.

A specific feature, mostly seen in psoriatic arthritis or inflammatory bowel disease, is dactylitis, where different small joints on one finger or toe are affected. In an important number of cases, subclinical gut inflammation with pathological findings resembling CD can be found, its presence ranging from 25 to 75% depending upon the type of SpA.4 Some of these patients (undifferentiated SpA with histological evidence of chronic gut inflammation) may eventually develop overt CD at a five years' follow up.5 ,6 In repeat ileocolonoscopy studies, clinical remission of articular symptoms was consistently associated with normalisation of gut histology, …