Ankylosing Spondylitis

• One of the seronegative spondyloarthropathies, others being Reiter's disease, Behçet's disease, psoriatic arthropathy, and arthropathy associated with inflammatory bowel disease (Crohn's and ulcerative colitis)

• Prevalence of 2:1000 in Western Europe but much lower in Japan and Negroid races

• M:F between 2:1 and 10:1

• Strong familial tendency

• Cause unknown but HLA-B27 found in 90% of patients and 50% of their relatives

 Pathology

• The preferential involvement of tendon and ligament insertions has coined the term Enthesopathy

• Two basic lesions

  1. Synovitis of diarthrodial joints

     • Synovitis of the SI joint and the facet joints causes destruction of articular cartilage and periarticular bone

     • The costovertebral joints are commonly affected which causes reduced respiratory excursion

     • When other joints are affected the same changes occur

  2. Inflammation of fibro-osseus junctions of syndesmotic joints

     • This affects the intervertebral discs, SI joint ligaments, manubriosternal joint, pubic symphysis and the bony insertions of large tendons

 Pathological changes occur in three stages

1. Inflammatory reaction with round cell infiltration, granulation tissue and destruction of bone

2. Replacement of the granulation tissue with fibrous tissue

3. Ossification of the fibrous tissue leading to ankylosis of joints