Characteristics

• Spondyloarthropathy affecting 5/1000 of the Caucasian population – only 10% develop significant symptoms.

• Predominantly a genetic aetiology (> 90%) with HLA B27 conferring a relative risk increase of 120, although this is not the only genetic inheritance factor in ankylosing spondylitis.

• Young adults, M : F = 3 : 1.

Clinical features

• Thoracolumbar and lower back pain with stiffness. Buttock pain with radiation down the posterior thigh but not below the knee.

• Morning stiffness and night pain are common.

• Costochondral/costovertebral pain, sometimes causing respiratory disease.

• Coexistent plantar fasciitis, iritis (30%), Achilles tendonopathy, inflammatory bowel disease (10%), psoriasis (10%) and major-joint involvement (20%). Cardiac problems occur in 1%.

• Progressive lumbar flattening and thoracic kyphosis, in conjunction with soft-tissue flexion contractures of the hip produce the characteristic ‘question mark’ posture.

• Further exacerbation of the thoracic kyphosis may be due to osteoporotic wedge fractures, which are not uncommon.

Radiological features

• Sacroiliitis is a pre-requisite for diagnosis. Look for early marginal sclerosis on the iliac side of the sacroiliac joint (SIJ), usually starting in the inferior 1/3 (synovial part) of the SIJ. Complete SIJ ankylosis is a late sign.

• Osteitis results in squaring of vertebral bodies. The earliest signs of spondylitis are manifest as small erosions at the corners of the vertebral bodies – the so-called Romanus lesion. Syndesmophyte formation eventually lead to classical ‘bamboo spine’.

• Osteoporosis and kyphosis occur with long-standing disease.

• Extra-axial skeletal involvement mimics mild rheumatoid arthritis.

Management

• NSAIDs and physiotherapy form the bulk of treatment.