Axial spondyloarthritis

Last revised by Jeremy Jones on 3 Apr 2024

Axial spondyloarthrititis (SpA) is a clinical subset of the seronegative spondyloarthritides that present primarily with back pain and morning stiffness. There is a long delay, on average 14 years, between symptoms onset and diagnosis 1.

The prevalence of axial SpA is ~1% 1. Age of onset is in the 3rd and 4th decades 2.

Assessment of SpondyloArthritis International Society (ASAS) criteria for the diagnosis of axial spondyloarthropathy 1:

  • ≥3 months of back pain and age of onset ≤45 years

  • sacroiliitis on imaging and ≥1 clinical feature or HLA-B27 and ≥2 clinical features

  • clinical features

    • inflammatory back pain: insidious onset; improvement with exercise but not with rest; night pain; morning back stiffness ≥30 minutes; alternating gluteal pain 2

    • arthritis

    • heel enthesitis

    • uveitis

    • dactylitis

    • psoriasis

    • Crohn disease

    • good response to NSAIDs (absent pain) 24-48 hours after a full dose 2

    • family history of SpA

    • elevated CRP

Imaging forms an important part of the work-up as the clinical features are somewhat non-specific 2. Radiographic evidence of SpA will be present in ~50% of patients at initial diagnosis. Some will progress to having radiographic evidence whilst others will never have radiographic evidence of SpA 1

Sacroiliac joint x-rays are the first-line modality. Definite radiographic sacroiliitis is characterized by the New York Criteria as bilateral grade 2 or unilateral grade 3 2

Sacroiliac joint MRI is the second line modality for assessment of potential sacroiliitis.

  • osteoarthritis: osteophytes, intra-articular gas, elderly patients

  • DISH (diffuse idiopathic skeletal hyperostosis) : osteophytes, intra-articular gas, absence of erosions, DISH elsewhere in the spine

  • osteitis condensans ilii: sclerosis, intra-articular gas, absence of erosions, female, multiparous

  • insufficiency fracture: elderly patients, absence of erosions, osteoporosis

  • septic arthritis: asymmetric, periarticular enhancement and soft tissue edema

  • normal growth plates in adolescents

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