Patients with nonradiographic axial spondyloarthritis (nr-axSpA) had lower levels of inflammation and a lower proportion of male patients when compared to patients with ankylosing spondylitis (AS), according to research published in Arthritis Care & Research. Both groups did not differ in health status, disease activity, and physical function.

Patients with axial SpA generally share a common genetic background and clinical characteristics, including spinal inflammation. The patients who have structural changes in the sacroiliac joints and spine are usually classified with AS, and patients without these changes have nr-axSpA.

To understand the differences between these subgroups, researchers compared the data of 100 consecutive patients with axial SpA who were not treated with tumor necrosis factor (TNF) antagonists. The data included patient-reported outcomes, C-reactive protein (CRP) levels to measure inflammation, and imaging to assess spinal inflammation by MRI and structural changes by conventional radiography.

Fifty-six patients were diagnosed with AS and 44 were diagnosed with nr-axSpA. Inflammation was higher among patients with AS than patients with nr-axSpA, with an average C-reactive protein level of 8.0 vs 3.8 mg/L and an average Ankylosing Spondylitis Disease Activity Score of 2.2 vs 2.8, respectively. The average number of spinal inflammatory lesions on MRI for patients with As was 2.0, vs 0.0 in the nr-axSpA group.

The researchers also observed that 76.8% of patients with AS were men, compared with 31.8% of patients with nr-axSpA.

The study suggests that the majority of nr-axSpA patients cannot be characterized as having preradiographic AS, but rather have “an abortive form characterized by typical SpA symptoms much like established AS, but with a female predominance, better function, and less structural changes.”

“We suggest not to regard patients with nr-axSpA as having preradiographic AS but rather as an axial SpA subgroup that is less prone to develop new bone formation,” the authors concluded. “However, our data also justify the inclusion of patients with nr-axSpA in the recent recommendations for anti-TNF therapy since the burden of disease was quite comparable in patients with nr-asSpA and established AF.”

Summary and Clinical Applicability

Patients with nr-axSpA and patients with AS did not differ in health status, disease activity, or physical function, but nr-axSpA patients had significantly lower levels of inflammation and affected fewer men than AS.  The data suggest that nr-axSpA patients cannot be categorized as having pre-radiographic AS.

Reference

Kiltz U, Baraliakos X, Karakostas P, et al. Do Patients With Non-Radiographic Axial Spondyloarthritis Differ From Patients with Anklylosing Spondylitis? Arthrit Care Res. 2016; 64(9): 1415-1422. doi: 10.1002/acr.21688.