Table 4.

Definitions of parameters applied in the Assessment of Spondyloarthritis International Society classification criteria for axial and peripheral spondyloarthritis

	Axial SpA ref. [11]	Peripheral SpA ref. [12]
IBP	According to experts (14): ≥4 out of 5 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)	IBP in the past according to the rheumatologist’s judgment.
		In patients with current IBP (and concomitant peripheral manifestations), the ASAS classification criteria for axial SpA should be applied
Arthritis	Past or present active synovitis diagnosed by a physician	Current peripheral arthritis compatible with SpA (usually asymmetric and/or predominant involvement of the lower limbs), diagnosed clinically by a doctor
Enthesitis	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.	Enthesitis: past or present spontaneous pain or tenderness at examination of an entheses.
		Any site of enthesitis can be affected whereas in the ASAS classification criteria for axial SpA only enthesitis of the heel is considered.
Uveitis	Past or present uveitis anterior, confirmed by an ophthalmologist
Dactylitis	Past or present dactylitis, diagnosed by a physician
Psoriasis	Past or present psoriasis, diagnosed by a physician
IBD	Past or present Crohn’s disease or ulcerative colitis diagnosed by a physician
Good response to NSAIDs	24–48 h after a full dose of a NSAID the back pain is not present any more or is much better	Not mentioned
Family history of SpA	Presence 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 CRP	CRP concentration above upper normal limit in the presence of back pain, after exclusion of other causes for elevated CRP concentration.	Not mentioned
HLA-B27	Positive testing according to standard laboratory techniques
Radiographic SI	Bilateral grade 2–4 or unilateral grade 3–4 sacroiliitis on plain radiographs, according to the modified New York criteria ref. [3]
SI by MRI	Active inflammatory lesions of sacroiliac joints with definite bone marrow edema/osteitis, suggestive of sacroiliitis associated with SpA
Preceding infection	NA	Urethritis/cervicitis or diarrhoea within 1 month before the onset of arthritis/enthesitis/dactylitis

SpA = spondyloarthritis. IBP = inflammatory back pain. ASAS = Assessment of SpondyloArthritis international Society. IBD = Inflammatory bowel disease. NSAIDs = non-steroidal anti-inflammatory drug. AS = ankylosing spondylitis. IBD = inflammatory bowel disease. CRP = C-reactive protein. MRI = magnetic resonance imaging.