Alternative diagnoses in patients with chronic back pain not diagnosed with axial spondyloarthritis: data from the SPACE cohort

Can rheumatologists unequivocally diagnose axial spondyloarthritis in patients with chronic back pain of less than 2 years duration? Primary outcome of the 2-year SPondyloArthritis Caught Early (SPACE) cohort

OBJECTIVES

To investigate the prevalence of axial spondyloarthritis (axSpA) in patients with chronic back pain (CBP) of less than 2 years (2y) duration referred to the rheumatologist, the development of diagnosis over time, and patient characteristics of those developing definite (d-)axSpA over 2y.

METHODS

We analysed the 2y data from SPondyloArthritis Caught Early, a European cohort of patients (<45 years) with CBP (≥3 months, ≤2y) of unknown origin. The diagnostic workup comprised evaluation of clinical SpA features, acute phase reactants, HLA-B27, radiographs and MRI (sacroiliac joints and spine), with repeated assessments. At each visit (baseline, 3 months, 1y and 2y), rheumatologists reported a diagnosis of axSpA or non-axSpA with level of confidence (LoC; 0-not confident at all to 10-very confident).

MAIN OUTCOME

axSpA diagnosis with LoC≥7 (d-axSpA) at 2y.

RESULTS

In 552 patients with CBP, d-axSpA was diagnosed in 175 (32%) at baseline and 165 (30%) at 2y. Baseline diagnosis remained rather stable: at 2y, baseline d-axSpA was revised in 5% of patients, while 8% 'gained' d-axSpA. Diagnostic uncertainty persisted in 30%. HLA-B27+ and baseline sacroiliitis imaging discriminated best 2y-d-axSpA versus 2y-d-non-axSpA patients. Good response to non-steroidal anti-inflammatory drugs and MRI-sacroiliitis most frequently developed over follow-up in patients with a new d-axSpA diagnosis. Of the patients who developed MRI-sacroiliitis, 7/8 were HLA-B27+ and 5/8 male.

CONCLUSION

A diagnosis of d-axSpA can be reliably made in nearly one-third of patients with CBP referred to the rheumatologist, but diagnostic uncertainty may persist in 5%-30% after 2y. Repeated assessments yield is modest, but repeating MRI may be worthwhile in male HLA-B27+ patients.

The Impact of Illness Perceptions and Coping on the Association Between Back Pain and Health Outcomes in Patients Suspected of Having Axial Spondyloarthritis: Data From the SPondyloArthritis Caught Early Cohort

OBJECTIVE

To investigate whether illness perceptions and coping influence the relationship between back pain and health outcomes in patients suspected of having axial spondyloarthritis (SpA).

METHODS

In the SPondyloArthritis Caught Early cohort, regression models were computed at baseline, with back pain intensity (range 0-10) as the determinant and health-related quality of life, the physical component summary score (PCS) and mental component summary (MCS) of the Short Form 36 (SF-36) health survey, or work productivity loss as outcomes. Subsequently, using Leventhal's Common-Sense Model of Self-Regulation, illness perceptions and, thereafter, coping were added to the models. Analyses were repeated for patients diagnosed and classified as having axial SpA according to the Assessment of SpondyloArthritis international Society axial SpA criteria (ASAS axial SpA), patients only diagnosed with axial SpA (axial SpA-diagnosed only), and those with chronic back pain.

RESULTS

A total of 424 patients (145 with ASAS axial SpA, 81 with only a diagnosis of axial SpA, and 198 with chronic back pain); 64% of the total group were female, the mean ± SD age was 30.9 ± 8.1 years, and the mean ± SD symptom duration was 13.3 ± 7.1 months) were studied. In all patients, the strength of the associations between back pain and the PCS, back pain and the MCS score, and back pain and loss of work productivity were decreased by adding illness perceptions to the model, but explained variance improved. Adding coping to these models did not change the results. Comparable results were observed in all subgroups.

CONCLUSION

Illness perception, but not coping, is important in the relationship between back pain and HRQoL and work productivity loss in patients suspected of having axial SpA, irrespective of subgroup. This finding suggests that targeting illness perceptions could improve health outcomes in patients suspected of having axial SpA.