Table 5 Definitions of parameters applied in the classification criteria for axial SpA
SpA featureDefinition
IBPIBP according to experts:14 at least four out of five parameters present: (1) age at onset <40 years; (2) insidious onset; (3) improvement with exercise; (4) no improvement with rest; (5) pain at night (with improvement upon getting up)
ArthritisPast or present active synovitis diagnosed by a physician
Enthesitis (heel)Heel enthesitis: past or present spontaneous pain or tenderness at examination of the site of the insertion of the Achilles tendon or plantar fascia at the calcaneus
UveitisPast or present uveitis anterior, confirmed by an ophthalmologist
DactylitisPast or present dactylitis, diagnosed by a physician
PsoriasisPast or present psoriasis, diagnosed by a physician
IBDPast or present Crohn’s disease or ulcerative colitis diagnosed by a physician
Good response to NSAID24–48 h after a full dose of a NSAID the back pain is not present any more or is much better
Family history of SpAPresence in first-degree (mother, father, sisters, brothers, children) or second-degree (maternal and paternal grandparents, aunts, uncles, nieces and nephews) relatives of any of the following: (1) AS; (2) psoriasis; (3) acute uveitis; (4) reactive arthritis; (5) IBD
Elevated CRPCRP concentration above upper normal limit in the presence of back pain, after exclusion of other causes for elevated CRP concentration
HLA-B27Positive testing according to standard laboratory techniques
Sacroiliitis by radiographsBilateral grade 2–4 or unilateral grade 3–4 sacroiliitis on plain radiographs, according to the modified New York criteria3
Sacroiliitis by MRIActive inflammatory lesions of sacroiliac joints with definite bone marrow oedema/osteitis, suggestive of sacroiliitis associated with SpA22
  • AS, ankylosing spondylitis; CRP, C-reactive protein; IBD, inflammatory bowel disease; IBP, inflammatory back pain; MRI, magnetic resonance imaging; NSAID, non-steroidal anti-inflammatory drug; SpA, spondyloarthritis.