Sacroiliitis by MRI or radiography* + 1 other feature
OR
HLA B27 + 2 other features
Features of axial SpA
Inflammatory back pain
4 of the 5 following characteristics
Age <40 years
Insidious onset
Improvement with exercise
No improvement with rest
Pain at night
Arthritis
Past or present active synovitis diagnosed by a physician
Enthesitis
Pain spontaneously or upon palpation of the Achilles tendon insertion site or plantar fascia
Uveitis
Past or present anterior uveitis diagnosed by a physician
Dactylitis
Past or present active dactylitis diagnosed by a physician
Psoriasis
Past or present active psoriasis diagnosed by a physician
Crohn's disease/ulcerative colitis
Past or present, diagnosed by a physician
Good response to NSAIDs
24–48 h after the initiation of full-dose NSAID therapy, the pain is gone or much better
Family history for SpA
First- or second-degree relative with any of the following: SpA, psoriasis, acute uveitis, reactive arthritis, chronic inflammatory bowel disease
HLA-B27
Presence of B27
Elevated CRP
CRP above the upper limit of the normal range, in the absence of another cause of CRP elevation
Sacroiliitis (X-rays or MRI): Definite radiographic sacroiliitis (grade 2 bilaterally or grade 3-4 unilaterally; according to modified New York criteria 1984) Or—active (acute) inflammation of sacroiliac joints on MRI, highly suggestive of sacroiliitis associated with spondyloarthritis.