MusculoskeletalPending review

Ankylosing Spondylitis

An HLA-B27-associated spondyloarthropathy in which inflammation begins at tendon and ligament entheses rather than the synovium, and the body's attempt to heal that inflammation lays down new bone that fuses the spine.

In a nutshell

Inflammation at tendon and ligament entheses, driven by HLA-B27-associated immune dysregulation, provokes a reparative bone-forming response that fuses the sacroiliac joints and spine over years. The inflammatory pattern of back pain (worse at night and with rest, improved by exercise) is the clinical clue that separates it from mechanical back pain.

Classic presentation

A young man under 45 with insidious low back and buttock pain, worse at night and in the morning, improving through the day with movement, morning stiffness over 30 minutes, and reduced spinal mobility.

Key points

The primary lesion is enthesitis (tendon/ligament insertion), not synovitis: this is why rheumatoid factor and anti-CCP are typically negative.

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Educational content pending clinical review. Not medical advice.