A Good Response to Nonsteroidal Antiinflammatory Drugs Does Not Discriminate Patients With Longstanding Axial Spondyloarthritis From Controls With Chronic Back Pain.

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To compare the response to nonsteroidal antiinflammatory drugs (NSAIDs) in patients with longstanding axial spondyloarthritis (axSpA) and controls with back pain (nonspondyloarthritis [non-SpA]). Consecutive outpatients with chronic back pain (axSpA or non-SpA), were prospectively recruited. Any previous NSAIDs were withdrawn 2 days before study start (baseline). Back pain was assessed using a numerical rating scale (NRS; range 0-10) starting at 2 hours after baseline and several times thereafter up to 4 weeks. "Any response" to NSAIDs was defined as improvement of back pain on the NRS > 2 units, and "good response" as improvement > 50%, compared to baseline. Among 233 patients included, 68 had axSpA (29.2%) and 165 had non-SpA back pain (70.8%). The mean age was 42.7 (SD 10.7) vs 49.3 (SD 11.1) years, symptom duration 15.1 (SD 11.1) years vs 14.6 (SD 11.9) years, and pain score 5.9 (SD 2.3) vs 6.3 (SD 2.0), respectively. Overall, of patients with axSpA or non-SpA back pain, 30.9% vs 29.1% of patients showed any response and 23.5% vs 16.4% of patients showed a good response after 4 weeks, respectively (P value not significant). No differences were found in the rapidity of response or between subgroups of patients based on demographics, including different stages of axSpA. No major differences in the response to NSAIDs were found between patients with axSpA and those with non-SpA with longstanding chronic back pain. The item in the Assessment of SpondyloArthritis international Society classification criteria on "response to NSAIDs" needs more study.