New guidance on diagnostic imaging for axial SpA

A new consensus statement on the imaging of axial spondylarthritis highlights the role of MRI in identifying patients with the controversial non-radiographic form of the condition.

Auckland District rheumatology trainee Dr Steven Truong said the statements were designed to provide practical guidance for clinicians while acknowledging that many questions about the natural history of non-radiographic axial spondylarthritis (SpA) remain unanswered.

“Historically, until the advent of MRI, we had difficulty making an early diagnosis for this group of patients and initiating usual treatment.”

“However we now have some wonderful MRI-based studies and mounting evidence that this is a real, important and treatable syndrome,” he said.

A panel of rheumatologists and radiologists from Australia and New Zealand with expertise in SpA developed the consensus statements from a thorough review of the literature around common questions.

The consensus recommends sacroiliac MRI for anyone under 45 years with inflammatory back pain or other features of axial SpA for longer than 3 months and no findings on pelvic radiography.

Dr Truong said the evidence did not show any additional value from a spinal MRI on patients with suspected SpA.

“In patients likely to have SpA, findings above the sacroiliac joint often don’t discriminate between other causes of back pain and this condition,” he said.

“But if a clinician is considering four or five possible diagnoses and the sacroiliac MRI is negative, then a bone scan or MRI of the upper spine may be of value.”

He said interpretation of sacroiliac changes have been far more consistent since 2009, following the definition of an ‘ASAS positive MRI’ for sacroiliitis.

Features assessed in an ‘ASAS positive sacroiliac MRI’ include bone marrow oedema but not structural lesions such as joint erosions.

Dr Truong said diagnosis of axial SpA was an evolving field but it would be a significant advance to be able to diagnose patients within months of symptom onset rather than the current average of 7-10 years.

“We would also like to be able understand their prognosis better – who will have significant pain or disability and who will respond well to treatment. At the moment we cannot confidently predict who will do worse.”

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