Definition

AS is a chronic and progressive inflammatory disease of the axial skeleton with sacroiliitis (usually bilateral) as its hallmark. Peripheral joints and extra-articular structures may also be affected. Most frequently presents in second or third decade more commonly in men; strong association with histocompatibility antigen HLA-B27.

Clinical Manifestations

• Back pain and stiffness: not relieved by lying down, often present at night forcing pt to leave bed, worse in the morning, improves with activity, insidious onset, duration >3 months (often called symptoms of “inflammatory” back pain).
• Extra-axial arthritis: hip and shoulders 25-35%, other peripheral joint involvement up to 30%, usually asymmetric.
• Chest pain: from involvement of thoracic skeleton and muscular insertions.
• Extra/juxta-articular pain: due to “enthesitis”: inflammation at insertion of tendons and ligaments into bone; frequently affects greater trochanter, iliac crests, ischial tuberosities, tibial tubercles, heels.
• Extra-articular findings-include acute anterior uveitis in up to 40% of pts, aortitis, aortic insufficiency, GI inflammation, cardiac conduction defects, amyloidosis, bilateral upper lobe pulmonary fibrosis.
• Constitutional symptoms: fever, fatigue, weight loss may occur.
• Neurologic complications: related to spinal fracture/dislocation (can occur with even minor trauma), atlantoaxial subluxation (can lead to spinal cord compression), cauda equina syndrome.

Physical Examination

• Tenderness over involved joints
• Diminished chest expansion
• Diminished flexion and extension of spine (Schober test measures lumbar spine flexion)

Evaluation

• ESR and C-reactive protein often elevated.
• Mild anemia.
• Rheumatoid factor and ANA negative.
• HLA-B27 may be helpful in pts with inflammatory back symptoms but negative x-rays.
• Radiographs: early may be normal. Sacroiliac joints: usually symmetric; bony erosions with “pseudowidening” followed by fibrosis and ankylosis. Spine: squaring of vertebrae; syndesmophytes; ossification of annulus fibrosis and anterior longitudinal ligament causing “bamboo spine.” Sites of enthesitis may ossify and be visible on x-ray. MRI is procedure of choice when plain radiographs do not reveal sacroiliac abnormalities and can show early intra-articular inflammation, cartilage changes, and bone marrow edema.

Diagnosis

(Table 163-1 ASAS Criteria for Classification of Axial Spondyloarthritis (To Be Applied for Pts with Back Pain 3 Months and Age of Onset 45 Years)a )