ObjectiveTo compare magnetic resonance images (MRIs) of the sacroiliac (SI) joints of healthy subjects and individuals with known mechanical strain acting upon the SI joints to those of patients with axial spondyloarthritis (SpA) and patients with chronic back pain.MethodsThree readers who had received standardized training and were blinded with regard to study group randomly scored MRIs of the SI joints of 172 subjects, including 47 healthy individuals without current or past back pain, 47 axial SpA patients from the Spondyloarthritis Caught Early (SPACE) cohort (with a previous MRI confirmed positive for sacroiliitis), 47 controls with chronic back pain (irrespective of MRI results) from the SPACE cohort, 7 women with postpartum back pain, and 24 frequent runners. MRIs were scored according to the Assessment of SpondyloArthritis international Society (ASAS) definition and Spondyloarthritis Research Consortium of Canada (SPARCC) index.ResultsOf the 47 healthy volunteers, 11 (23.4%) had an MRI positive for sacroiliitis, compared to 43 (91.5%) of 47 axial SpA patients and 3 (6.4%) of 47 patients with chronic back pain. Three (12.5%) of the 24 runners and 4 (57.1%) of the 7 women with postpartum back pain had a positive MRI. Using a SPARCC cutoff of ≥2 for positivity, 12 (25.5%) of 47 healthy volunteers, 46 (97.9%) of 47 positive axial SpA patients, 5 (10.6%) of 47 controls with chronic back pain, 4 (16.7%) of 24 runners, and 4 (57.1%) of 7 women with postpartum back pain had positive MRIs. Deep bone marrow edema (BME) lesions were not found in healthy volunteers, patients with chronic back pain, or runners, but were found in 42 (89.4%) of 47 positive axial SpA patients and in 1 (14.3%) of 7 women with postpartum back pain.ConclusionA substantial proportion of healthy individuals without current or past back pain has an MRI positive for sacroiliitis according to the ASAS definition. Deep (extensive) BME lesions are almost exclusively found in axial SpA patients.

Objective. To identify axial spondyloarthritis (SpA) in Dutch primary care patients with chronic low back pain (CLBP), and to design a simple referral model for general practitioners (GPs) that would identify patients at risk for axial SpA. Methods. Patients (ages 20 -45 years) with CLBP were identified from GP records. Assessments included inflammatory back pain questionnaires, medical interviews, physical examinations, HLA-B27, C-reactive protein level, conventional radiography, and magnetic resonance imaging. The outcome measure was axial SpA defined by the Assessment of SpondyloArthritis international Society (ASAS) criteria. Multivariable regression analysis with bootstrapping was used to develop the referral model. Results. A total of 364 patients (mean ؎ SD age 36.3 ؎ 6.8 years) was recruited with a median symptom duration of 9.0 years. Eighty-six patients (24%) fulfilled the ASAS criteria for axial SpA. Of all potential determinants, the ASAS inflammatory back pain questionnaire, good response to nonsteroidal antiinflammatory drugs, family history of SpA, and symptom duration were identified as most relevant for diagnosing axial SpA by multivariable regression analysis related to axial SpA. The shrunken regression coefficients were, respectively, 1.04, 0.83, 0.73, and 0.23. The combination of these 4 items proved a useful area under the receiver operating characteristic curve of 0.75 (SE 0.03). In a simplified score model, at the suggested cutoff value of 1.5, the sensitivity was 83% and specificity was 59%. Conclusion. This study shows that 1 of 4 primary care patients with CLBP was classified as having axial SpA. A preselection in primary care based on a combination of clinical items may be useful to facilitate the identification of patients at risk of axial SpA.

ObjectivesTo validate and optimize a referral rule to identify primary care patients with chronic low back pain (CLBP) suspected for axial spondyloarthritis (axSpA).DesignCross-sectional study with data from 19 Dutch primary care practices for development and 38 for validation.ParticipantsPrimary care patients aged 18-45 years with CLBP existing more than three months and onset of back pain started before the age of 45 years.Main OutcomeThe number of axSpA patients according to the ASAS criteria.MethodsThe referral rule (CaFaSpA referral rule) was developed using 364 CLBP patients from 19 primary care practices and contains four easy to use variables; inflammatory back pain, good response to nonsteriodal anti-inflammatory drugs, family history of spondyloarthritis and a back pain duration longer than five years. This referral rule is positive when at least two variables are present. Validation of the CaFaSpA rule was accomplished in 579 primary care CLBP patients from 38 practices from other areas. Performance of the referral rule was assessed by c-statistic and calibration plot. To fit the final referral rule the development and validation datasets were pooled leading to a total study population of 943 primary care participants.ResultsThe referral rule was validated in 579 patients (41% male, mean age 36 (sd7.0). The percentage of identified axSpA patients was 16% (n=95). External validation resulted in satisfactory calibration and reasonable discriminative ability (c-statistics 0.70 [95% CI, 0.64-0.75]). In the pooled dataset sensitivity and specificity of the referral rule were 75% and 58%.ConclusionsThe CaFaSpA referral rule for axSpA consists of four easy to use predictors for primary care physicians and has a good predictive value in this validation study. The referral rule has the potential to be a screening tool for primary care by identifying CLBP patients suspected for axSpA.