Ankylosing spondylitis

It is typical appearance of bamboo spine seen in ankylosis spondylitis.

Ankylosing spondylitisis the prototype of the Spondyloarthropathy and one of the common rheumatic diseases. Sacroiliitis is the earliest recognised manifestation of Ankylosing spondylitis, but peripheral joints and extra-articular structures may also be affected. Subchondral tissues become granulomatous and infiltrated with plasma cells, lymphocytes, mast cells, macrophages, and chondrocytes. The affected joints show irregular erosion and sclerosis. Tissue is gradually replaced by fibrocartilage and then becomes ossified. When these lesions occur in the spine, the junction of the annulus fibrosus of the disc cartilage and the margin of the vertebral bone undergo irreversible damage. The outer annular fibres are replaced by bone and the vertebrae become fused. In advanced stages of the disease the fusion typically ascends the spine, forming a long bony column referred to as “bamboo spine.”

Pathogenesis

The pathogenesis of Ankylosing spondylitis is poorly understood. Immune mediated mechanisms are suggested by inflammatory histology, raised serum levels of IgA and acute phase reactants, and the close relationship between HLA-B27 and Ankylosing spondylitis. No single agent or event has been identified as the cause of the disease, but the interrelationship between Ankylosing spondylitis, Rheumatoid arthritis, and Inflamatory bowel disease suggests that enteric bacteria may play a part.

Signs and symptoms

Chronic back pain and progressive spinal stiffness are the most common features of the disease. Involvement of the spine and sacroiliac joints, peripheral joints, digits, entheses are characteristic of the disease. Impaired spinal mobility, postural abnormalities, buttock pain, hip pain, peripheral arthritis, enthesitis, and dactylitis (“sausage digits”) are all associated with AS.

Extraskeletal organs may also be affected by this disease. The most common extraarticular manifestations of Ankylosing spondylitis include inflammatory bowel disease (up to 50%), acute anterior uveitis (25% to 35%), and psoriasis (approximately 10%). Ankylosing spondylitis is also associated with an increased risk of cardiovascular disease. The cause of this increased risk has been postulated to be due to the systemic inflammation evident in Ankylosing spondylitis. Pulmonary complications are also associated with Ankylosing spondylitis, as diminished chest wall expansion and decreased spinal mobility predispose patients to a restrictive pulmonary pattern.

Finally, Ankylosing spondylitis predisposes people to at least a two-fold increased incidence of vertebral fragility fractures. These patients are also at increased risk of atlantoaxial subluxation, spinal cord injury, and, rarely, cauda equina syndrome.

Diagnostic criteria

Modified New York Criteria for Ankylosing Spondylitis

 Radiologic criteria : Sacroiliitis, grade >II bilaterally or grade III to IV unilaterally

Clinical criteria : Low back pain and stiffness for more than 3 months that improves with exercise but is not relieved by rest Limitation of motion of the lumbar spine in both the sagittal and frontal planes Limitation of chest expansion relative to normal values correlated for age and sex.

Treatment and management

Treatment goals should focus on relieving pain and stiffness, maintaining axial spine motion and functional ability, and preventing spinal complications. Non-pharmacologic interventions should include regular exercise, postural training, and physical therapy. First-line medication therapy is with long-term, daily non-steroidal anti-inflammatory drugs (NSAIDs). Should NSAIDs not provide adequate relief, they can be combined with or substituted for tumor necrosis factor inhibitors (TNF-Is) such as adalimumab, infliximab, or etanercept. Response to NSAIDs should be assessed 4 to 6 weeks after initiation and 12 weeks following initiation of TNF-Is. Systemic glucocorticoids are not recommended, but local steroid injections may be considered. Specialist referrals may be warranted based on the patient’s clinical picture, potential complications, and/or extra-articular manifestations of the disease. Rheumatologists may assist in a formal diagnosis, management, and monitoring, while dermatologists, ophthalmologists, and gastroenterologists may assist with associated non-musculoskeletal features of Ankylosing spondylitis.