- Ankylosing spondylitis (AS) is an axial inflammatory spondyloarthropathy (axSpA) characterized by chronic low back pain (>3 months duration) and evidence of sacroiliitis (sclerosis, erosions, and changes in joint width) on plain radiography.
- Systems affected: musculoskeletal; ophthalmic; cardiovascular; neurologic; pulmonary
- Synonyms: Marie–Strümpell disease; “bamboo spine”
- Peak age of onset 20 to 30; rarely occurs after age 40 years
- Male > female (approximately 2 to 3:1)
Age- and gender-adjusted rate of 6.3 to 7.3/100,000 person-years
~0.55% for AS and ~1.4% for all axSpA in the United States (1)
Etiology and Pathophysiology
- Autoinflammation at sites of bacterial exposure (e.g., intestines) or mechanical stress in genetically susceptible individuals (2)
- Inflammation at the insertion of tendons, ligaments, and fasciae to bone (enthesopathy) causes erosion, remodeling, and new bone formation.
- 85–95% of patients with AS are HLA-B27positive.
- Other genetic associations include endoplasmic reticulum aminopeptidase 1 (ERAP1), interleukin-23 receptor (IL23R), and gene deserts on chromosome 2p15 and 21q22 (2).
Positive family history
- HLA-B27–positive child of a parent with AS has a 10–30% risk of developing the disease.
Commonly Associated Conditions
- Peripheral arthritis (30%)
- Enthesopathy (29%): Achilles tendonitis, plantar fasciitis
- Uveitis (25–35%)
- Psoriasis (10%)
- Dactylitis “sausage digit” (6%)
- Peripheral spondyloarthritis (SpA): psoriatic arthritis, reactive arthritis, IBD-related arthritis, juvenile idiopathic arthritis
- Aortitis, aortic regurgitation, and cardiac conduction defects
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