• ankylosing spondylitis
• disease controlling antirheumatic drugs
• tumour necrosis factor α
• biological agents

Ankylosing spondylitis (AS) is primarily an inflammatory arthritis of the back, affecting the sacroiliac and apophysial joints.¹ The age of onset is usually late teens with men being affected nine times more than women. Onset is gradual with pain and stiffness in the low back, characteristically at night or early morning.² The natural history of AS is progression to affect the whole spine, resulting in spinal deformities. These include flattening of the lumbar lordosis, kyphosis of the thoracic spine, and hyperextension of the cervical spine, with eventual flexion contractures of the hips and knees and significant morbidity and disability. These clinical features are mirrored by the radiological changes of syndesmophytes and ankylosis of the spine as well as erosive changes, sclerosis, and eventual ankylosis of the sacroiliac joints.³

Peripheral arthritis occurs uncommonly in AS, and when it occurs, it is usually late in the course of the arthritis.⁴ The development of peripheral arthritis early in the course of the disease is a predictor of disease progression.⁵ The arthritis usually presents in the lower extremities in an asymmetric distribution. Involvement of the “axial” joints, including shoulders and hips, is more common than involvement of more distal joints. In the shoulder, there may be a unique lesion of erosion at insertion of the rotator cuff.⁶ In the hips, progressive flexion deformity and eventual destruction of the joint may occur. In addition, enthesitis, or inflammation at sites of tendon insertion into bone, is common, affecting primarily plantar fascia and Achilles tendon insertion. The disease is often complicated by the presence of iritis (particularly anterior uveitis), cardiac manifestations (including dilatation of the root of the aorta and conduction defects), …