Table 1 SpA classification criteria

Inflammatory spinal pain OR synovitis (asymmetric or predominantly lower limb)

Sacroiliitis on imaging plus ≥ 1 SpA feature

OR

HLA-B27 plus ≥ 2 other SpA features

Definite AS if radiological criterion is associated with at least one clinical criterion.

AND one or more of the following:

Clinical criteria:

 • Positive family history

SpA features:

• Low back pain and stiffness for > 3 months that improves with exercise but is not relieved by rest.

 • Psoriasis

Inflammatory back pain,

 • Inflammatory bowel disease

arthritis, enthesitis (heel), uveitis, dactylitis,

 • Urethritis, cervicitis or acute diarrhoea within 1 month before arthritis

psoriasis, Crohns/colitis, good response to NSAIDs, family history for SpA, HLA-B27, elevated CRP

• Limitation of motion of the lumbar spine in the sagittal and frontal planes.

 • Buttock pain alternating between right and left gluteal areas

• Limitation of chest expansion relative to normal values correlated for age and sex.

 • Enthesopathy

 • Sacroiliitis

Sacroiliitis on imaging:

Definite radiographic sacroiliitis according to mNY criteria.

Radiological criterion:

OR

Active (acute) inflammation on MRI highly suggestive of sacroiliitis associated with SpA.

 • Sacroiliitis grade ≥ 2 bilaterally or 3–4 unilaterally.