Percentage of patients with spondyloarthritis in patients referred because of chronic back pain and performance of classification criteria: experience from the Spondyloarthritis Caught Early (SPACE) cohort

TLDR: The inclusion criteria of the SPACE cohort yield the same high numbers of SpA patients compared with referral strategies like inflammatory back pain, HLA-B27+ or sacroiliitis, yet are easier to apply.

Abstract: Objectives. The objectives of the study are to describe the Spondyloarthritis Caught Early (SPACE) cohort, present the performance of various SpA classification criteria and compare patients fulfilling the imaging arm with patients fulfilling the clinical arm of the Assessment of Spondyloarthritis international Society (ASAS) axSpA criteria on demographics, presence of SpA features and level of disease activity. Methods. Patients with back pain (53 months but 42 years, onset <45 years) visiting the rheumatology outpatient clinic of the Leiden University Medical Center were included in the SPACE cohort. Patients were classified according to the modified New York (mNY), ESSG, Amor and ASAS axSpA criteria. The sensitivity and specificity of criteria were tested against a rheumatologist’s diagnosis. Results. In total, 157 patients were included; 92 patients fulfilled any criteria, 11 fulfilled the mNY (sensitivity 16.9%, specificity 100%), 68 the ESSG (sensitivity 64.6%, specificity 71.7%), 48 the Amor (sensitivity 47.7%, specificity 81.5%) and 60 the ASAS axSpA criteria (sensitivity 84.6%, specificity 94.6%). Of those 60 patients, 30 fulfilled the imaging arm and 30 the clinical arm. Patients in the imaging arm are statistically significantly more often male, have a longer symptom duration and less often a positive family history for SpA than patients fulfilling the clinical arm. Patients in both arms are very similar regarding all other SpA features and level of disease activity. Conclusion. The inclusion criteria of the SPACE cohort yield the same high numbers of SpA patients compared with referral strategies like inflammatory back pain, HLA-B27+ or sacroiliitis, yet are easier to apply. The ASAS axSpA criteria outperformed the other criteria; 38.2% fulfilled the ASAS axSpA criteria. Patients fulfilling the clinical arm of the ASAS axSpA reflect a group of patients similar to those fulfilling the imaging arm.