Axial Spondyloarthritis (axSpA)
What is Axial Spondyloarthritis? What is its relationship to AS?
Axial Spondyloarthritis is a chronic, systemic inflammatory disease affecting the sacroiliac joints, spine, and, occasionally peripheral joints.
Sacroiliitis evident on plain radiographs is characteristic of AS—the more advanced presentation of the disease. However, it typically takes 4 to 9 years from the onset of inflammatory back pain until the development of definite radiographic sacroiliitis. Patients with axSpA without clear sacroiliitis on plain radiograph usually have inflammation detected on MRI. These patients are said to have a “nonradiographic” axSpA, which may or may not progress over time to definite radiographic sacroiliitis. The Assessment of SpondyloArthritis International Society (ASAS) classification criteria were developed for patients with back pain for >3 months and age of onset <45 years in order to identify early disease (i.e., no clear sacroiliitis on radiographs). These criteria have a sensitivity of 83% and specificity of 84% for a patient with axSpA.
| Sacroiliitis on imaging | HLA-B27 | |
| Plus | OR | Plus |
| ≥1 SpA feature | ≥ 2 other SpA features | |
| • SpA features: inflammatory back pain, arthritis, enthesitis (heel), uveitis, dactylitis, psoriasis, Crohn’s disease/ulcerative colitis, good response to nonsteroidal antiinflammatory drugs (NSAIDs), family history for SpA, HLA-B27, elevated C-reactive protein (CRP) | ||
| • Sacroiliitis on imaging: active (acute) inflammation on MRI showing sacroiliitis; or definite radiographic sacroiliitis |
