Early diagnosis crucial in ankylosing spondylitis

Ankylosing spondylitis (AS) is an inflammatory autoimmune disorder that predominantly affects the spine. If untreated it may cause significant morbidity. Early diagnosis is particularly important as newer therapies are able to contain this condition and even induce remission. AS affects about 0.2-0.5% of the population. It is at least twice as common in men and most often manifests in the third to fifth decades. It is estimated that up to 5% of patients with chronic lower back pain in primary care have inflammatory disease. Although only 1% of patients with HLA-B27 develop AS, 90-95% of patients with AS are positive for HLA-B27. Immune dysfunction is the hallmark of this condition and it may be triggered by infection. The primary site of inflammation in AS is the entheses, the sites of insertion of tendons and ligaments into bone. If the inflammation remains untreated, there is resultant fibrosis and ultimately ossification at the entheseal sites. AS should be suspected in patients who report back pain and stiffness with rest, especially in the morning, which improves with exercise. Although the condition affects both the sacroiliac joints, a proportion of patients report pain radiating into the buttocks which may be unilateral or alternate, particularly in the early stages. In addition to the spine, large joint synovitis may develop as well as features of entheseal involvement. New classification criteria take into account early sacroiliitis evident on MRI scan and allow a diagnosis to be made far earlier than was previously possible. A proportion of patients respond well to NSAIDs coupled with a structured physiotherapy and exercise programme. However, about half these patients need escalation to biologic therapy. Patients with a suspected diagnosis should be referred to secondary care in order to confirm the diagnosis and commence treatment.