Chronic vs Inflammatory Back Pain: How Best to Distinguish Early SpA?

van den Berg R, de Hooge M, van Gaalen, et al., Percentage of patients with spondyloarthritis in patients referred because of chronic back pain and performance of classification criteria: experience from the Spondyloarthritis Caught Early (SPACE) cohort.Rheumatology (2013) 52: 1492-1499

Chronic back pain is so common that radiographic evidence of inlammatory back pain is often used to diagnose early axial spondylitis (axSpA). But Dutch researchers say that use of imaging alone could miss 20% of all spondyloarthritis (SpA) cases.

The researchers note that the clinical presentation of axSpA is very heterogeneous, with no single distinguishing feature, making it a challenge to judge which patients with back pain have the condition. It’s generally believed that specific radiographic inflammatory back pain (IBP) is typical of the disorder, so rheumatologists may weigh positive imaging as very important in their diagnostic judgments about this condition.

However, a comparison of four clinical diagnostic criteria applied by rheumatologistswith radiographic images from 157 patients in the ongoing SpondyloArthritis Caught Early (SPACE) cohort study at Leiden University Medical Center found that IBP is not a strong discriminating feature of SpA.

The study compared patients meeting any of four different clinical criteria for SpA--the modified New York criteria, the European Spondyloarthropathy Study Group (ESSG), the Amor criteria, and the more recently established Assessment of Spondyloarthritis International Society (ASAS) criteria--with those deemed positive for SpA by two of three readers based on MRI or radiography images. Patients classified as positive for SpA at baseline by any of these criteria were followed up at 3, 12 and 24 months.

The SPACE cohort is unique, in that it has only one criterion for inclusion: almost-daily back pain of short duration before age 45. Among axSpA patients, 41.1% meet this criterion, yielding the same number of SpA patients as referral strategies that include IBP.

Almost 40% of patients in the cohort fulfilled the recently established Assessment of Spondyloarthritis International Society (ASAS) criteria.

Analysis of the cohort found that, while around 80% of the axSpA patients in the SPACE cohort had IBP, it was also present in 56.7% of patients who do not have SpA. Among patients judged positive for SpA by imaging, men were more common and symptom duration was longer, but disease activity was similar to those judged positive by clinical measures.

The bottom line? The simple one-measure clinical assessment of almost-daily back pain before age 45 appears as good as the ASAS clinical criteria for judging the presence of SpA, and both are somewhat more reliable than imaging studies in detecting the condition.