Baraliakos X, et al. – In this study, the physicians compared the performance of currently used classification criteria in patients diagnosed with axial spondyloarthritis (axSpA) or fibromyalgia (FM). They observed that FM patients only rarely fulfil classification criteria for axSpA, whereas, some axSpA patients also fulfil FM criteria. Since this was more frequent in patients with AS it might be associated with the severity and duration of chronic pain in axSpA patients. These findings indicated that assessment instruments analyzed in axSpA were not disease-specific.

Methods

• This study consisted of patients diagnosed with axSpA or FM by the treating rheumatologist and evaluated by an independent examiner for fulfilment of the classification criteria for axSpA (ASAS criteria) and/or FM (1990 ACR classification and 2010 ACR diagnostic criteria).
• Patients with axSpA were stratified based on classification as non-radiographic axSpA (nr-axSpA) or AS.
• With established disease-related questionnaires, symptom severity was evaluated.

Results

• In total, 300 patients were enrolled, 100 with FM and 200 with axSpA of which 100 each had nr-axSpA and AS.
• Findings revealed that almost all FM patients fulfilled the 2010 (100%) and 1990 ACR criteria (98%) for FM, but only 2% fulfilled the ASAS criteria.
• When calculations were based on only the FM patients with available HLA-B27 results (n = 40), the proportion fulfilling the ASAS criteria was 5%.
• All axSpA patients met the ASAS criteria but also the 2010 (24%) and 1990 (13.5%) FM criteria.
• More patients with AS (29% and 19%) than with nr-axSpA (19% and 8%) fulfilled the 2010 and 1990 FM criteria, respectively.