The Assessment of Spondyloarthritis International Society (ASAS) classifies more patients with spondyloarthritis (SpA) when the rheumatologist’s diagnosis is used as an external standard, according to data from a Colombian cohort published in Clinical Rheumatology.
Multiple sets of SpA classification criteria such as the European Spondylarthropathy Study Group (ESSG) and the Amor criteria have been developed for clinical studies. However, these classifications were designed to classify patients along the whole disease spectrum and are not as effective for early recognition of the disease. The ASAS criteria were developed to better distinguish between axial SpA and peripheral SpA when classifying patients.
“By default, classification criteria in clinical practice should be applied to patients [who] have been diagnosed by the rheumatologist; they are not diagnostic criteria,” the authors noted. “Because of the nature of classification criteria, it can be expected that sensitivity is relatively low, but if performing well, specificity should be high.”
To investigate the performance of these classification criteria sets, researchers calculated the proportion of patients fulfilling a particular criterion. In the Colombian cohort, patients were included in the study after receiving a clinical SpA diagnosis from a rheumatologist. The cohort was further analyzed for characteristics of the 3 criteria sets.
The researchers found that the ASAS criteria classified 81% of all patients included in the study (N=581) as having axial SpA (44%) or peripheral SpA (37%). Only 74% of patients met ESSG criteria, while 53% met Amor criteria. Researchers also noted that 42% of patients met all 3 criteria.
The patients who were classified using all 3 criteria were typically older than the patients who did not meet any of the criteria (36 vs 30 years). These patients also had more SpA features (3 vs 1 feature) and a history of back pain (77% vs 43%), inflammatory back pain (47% vs 13%), enthesitis (67% vs 26%), and buttock pain (37% vs 13%).
Researchers also performed HLA-B27 testing in 77% of the patients and found that 43.9% were positive. Radiographs were also obtained in 59% of patients, and magnetic resonance imaging (MRI) of the sacroiliac joint was obtained in 24% of patients.
The ASAS criteria still proved to be more sensitive than the other classification criteria sets, even when the ESSG and Amor were given additional information about active inflammatory changes on MRI as a feature of SpA.
Summary and Clinical Applicability
The ASAS criteria classify more patients with axial or peripheral SpA when compared with the ESSG and Amor criteria. A rheumatologist’s diagnosis should be used as an external standard, and classification criteria should be tested against the judgment of the rheumatologist.
Bautista-Molano W, Landewe R, Londono J, et al. Analysis and performance of various classification criteria sets in a Colombian cohort of patients with spondyloarthritis. Clin Rheumatol. 2016; doi: 10.1007/s10067-016-3184-2.