Define Ankylosing Spondylitis. Describe its clinical features, investigations, management and complications.

Definition

Ankylosing spondylitis (AS) is a chronic seronegative inflammatory arthropathy that principally affects the axial skeleton — the sacroiliac joints and spine — leading to inflammation, ossification and progressive bony ankylosis. It is the prototype of the seronegative spondyloarthropathies and is strongly associated with HLA-B27. It typically affects young men in the second and third decades.

Clinical Features

The hallmark is inflammatory back pain: insidious onset in a young adult, worse in the morning and with rest, improved by exercise, with prolonged morning stiffness and buttock pain (sacroiliitis). As the disease progresses the spine stiffens, with loss of lumbar lordosis, a fixed thoracic kyphosis and reduced chest expansion; advanced disease produces the rigid ‘bamboo spine’ and the stooped ‘question-mark’ posture. A reduced Schober’s test quantifies loss of lumbar flexion.

Extra-articular Features (the ‘a’s)

AS has systemic associations conveniently remembered as Anterior uveitis (the commonest extra-articular feature), Aortic regurgitation and conduction defects, Apical pulmonary fibrosis, Achilles tendinitis/enthesitis, Amyloidosis, and Atlanto-axial subluxation. Peripheral arthritis and enthesitis (plantar fasciitis) also occur.

Investigations

• Radiographs of the sacroiliac joints show sacroiliitis (erosions, sclerosis, later fusion) — the earliest and most important sign
• the spine shows syndesmophytes bridging vertebrae (the ‘bamboo spine’), squaring of vertebral bodies and ligamentous ossification.
• MRI detects early sacroiliitis before radiographic change.
• HLA-B27 is usually positive
• rheumatoid factor is negative (seronegative)
• ESR/CRP may be raised.

Management

There is no cure; management aims to control pain and inflammation and preserve posture and mobility. The cornerstone is regular exercise and physiotherapy (to maintain spinal extension and chest expansion) together with NSAIDs for symptom control. Biologic agents (anti-TNF, IL-17 inhibitors) are highly effective for active disease not controlled by NSAIDs. Conventional DMARDs help peripheral (not axial) disease. Surgery (corrective osteotomy for severe kyphosis, hip replacement for hip involvement) is reserved for advanced deformity or joint destruction.

Diagnostic Criteria & Course

AS is one of the seronegative spondyloarthropathies, a family that also includes psoriatic arthritis, reactive arthritis and enteropathic (IBD-associated) arthritis, sharing features such as HLA-B27 association, enthesitis, dactylitis and sacroiliitis. The diagnosis rests on inflammatory back pain, restricted spinal movement and reduced chest expansion supported by imaging evidence of sacroiliitis. The course is one of intermittent flares over decades; early diagnosis and sustained exercise are the best predictors of preserved function.

Complications

Advanced disease leads to a rigid, kyphotic spine with impaired posture, forward gaze and respiratory reserve; the fused spine is brittle and prone to unstable fracture after minor trauma. Systemic complications include anterior uveitis, aortic regurgitation, apical pulmonary fibrosis and, rarely, amyloidosis and cauda equina syndrome. Osteoporosis of the ankylosed spine compounds the fracture risk.

Inflammatory back pain improves with exercise, worsens with rest.

• Seronegative axial spondyloarthropathy; HLA-B27; young men; sacroiliitis is the key lesion.
• Inflammatory back pain: worse with rest, better with exercise; ‘bamboo spine’, reduced Schober’s.
• Extra-articular ‘A’s: Anterior uveitis, Aortic regurgitation, Apical fibrosis, etc.
• SI-joint X-ray/MRI; syndesmophytes; HLA-B27+, RF negative.
• Exercise + NSAIDs ± biologics; ankylosed spine fractures easily and unstably.