A 23-year-old male player presented with a two-year history of low back pain and stiffness. He was unable to identify a discrete precipitant, but thought that it started during football. His symptoms initially seemed to improve with physiotherapy however they never resolved. He described central and left sided pain that would wake him from sleep most nights, and was generally worse in the morning. It would typically warm up during the day and he had been able to continue to play. He had a mild restriction in his lumbar flexion range of motion but otherwise did not appear to have any significant examination findings.
An x-ray series of the lumbar spine, hip and pelvis was essentially normal. There is abnormal T2 hyperintensity centred on the left sacroiliac joint on MRI sequences. This affects both the iliac and sacral side of the joint. The possibility of an erosion at the inferior margin on the iliac side of the joint is raised. This is no adjacent soft tissue oedema. The right sacroiliac joint appears normal. At the time of his initial presentation a full blood count was normal, as were his CRP and ESR. He was HLA-B27 positive.
Further questioning of this player revealed that a maternal aunt had been diagnosed with ankylosing spondylitis (AS) in her thirties. There was no history of any recent illnesses and no other significant past medical problems. Based on his history and his MRI findings a provisional diagnosis of AS was made. He was started on regular oral NSAID. His symptoms dramatically improved and resolved within two weeks of starting this treatment. He was referred to a rheumatologist to help confirm the diagnosis and to consider the role of disease modifying agents.
Sacroiliitis is commonly the first indicator of AS and other types of spondyloarthritis. Classically the sacroiliitis associated with AS is bilateral and symmetric. Unilateral involvement is however relatively common in the early stages of the disease and is also present with psoriatic arthritis and in patients with reactive arthritis (as well as with other types of pathology including infection, osteoarthritis and trauma).
The diagnosis of spondyloarthropathies is based primarily on a patient’s history and physical examination. An absence of trauma and an inflammatory pattern of pain (improved by exercise, not relieved by rest) should prompt you to consider this type of pathology. There are no specific diagnostic tests however there are a range of laboratory and radiological tests that can be used to support a patient’s diagnosis. When present an elevated white cell count, ESR or CSP can help establish a diagnosis. As this case illustrates however, these tests can frequently be normal. MRI is among the most sensitive tests for diagnosing sacroiliitis. The four MRI findings of active sacroiliitis are osteitis or bone marrow oedema, enthesitis, capsulitis and synovitis. Osteitis or bone marrow oedema is considered the single most important diagnostic criterion.
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