Axial spondyloarthropathy (axSpA), a chronic form of arthritis in the lower back, often causes inflammation in one’s sacroiliac joints, which connects the sacrum to the pelvis.

But a retroactive study of MRI showed inflammation also can be seen in healthy individuals and not only those affected by axSpA, demonstrating the importance of other diagnostic measures.

“Sacroiliac MRI has become an important aid in diagnosing spondyloarthritis, because sacroiliac joint inflammation and damage are hallmarks of this disease. Unfortunately, physicians all too often pay too much attention to a positive MRI, and consider it a decisive feature in the diagnosis,” wrote Landewé, MD, PhD, professor of rheumatology at the University of Amsterdam in the Netherlands, and colleagues. “We have learned that sacroiliac MRI can also be positive in unaffected, or healthy, individuals.”

The study was published online Nov. 4 in Arthritis & Rheumatology, the journal of the American College of Rheumatology. Landewé also presented results at the 2017 ACR/Association of Rheumatology Health Professionals Annual Meeting in San Diego.

The researchers had three readers score a collection of sacroiliac MRI scans of 172 people—47 healthy individuals, 47 matched axSpA patients, 47 matched chronic back pain patients, seven women with postpartum back pain and 24 frequent runners. The readers scored the scans Assessment of Spondyloarthritis (ASAS)/Outcome Measures in Rheumatology (OMERACT) and the Spondyloarthritis Research Consortium of Canada (SPARCC) definitions. The SPARCC scores were the mean results from all three readers.

The readers agreed on the presence or absence of bone marrow edema in 75.6 to 79.9 percent of cases. In total, 11 of the 47 healthy patients and 13 of the 47 axSpA patients had positive MRI. Three of 47 chronic back pain patients and three of 24 runners also had positive MRI. Four of the seven women with postpartum back pain also had positive results.

Mean SPARCC scores were 1.7 for the healthy individuals, 20.9 for the positive axSpA patients, 0.8 for the chronic back pain patients, 0.8 for the frequent runners and 4.5 for the women with postpartum back pain.

“This study provides an estimate of how frequently positive sacroiliac MRIs can be found in individuals without SpA, or specificity,” said Landewé. “Rheumatologists now better realize that they cannot make a diagnosis of SpA solely based on a positive MRI.”