Two scores used to measure disease activity in axial psoriatic arthritis are similarly accurate, but the older measure is easier to employ and thus, probably more clinically practical, a study has shown.
A comparative study determined that the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), with its single patient-derived format of six questions, is just as accurate as the newer Ankylosing Spondylitis Disease Activity Score (ASDAS). That measure has four formulas including two that assess both C-reactive protein (CRP) level and erythrocyte sedimentation rate (ESR), and two that assess each of the factors separately.
ASDAS was introduced in 2007 because researchers felt the BASDAI had limited face and construct validity, reported Dr. Lihi Eder and colleagues (Ann. Rheum. Dis. 2010 July 13 [doi:10.1136/ard.2010.129726]).
Dr. Eder of Toronto Western Hospital and the coauthors compared the scores’ validity in 201 patients with axial psoriatic arthritis. Their mean age was 53 years; the mean duration of psoriatic arthritis was 18.5 years, with a mean of 9 years since the diagnosis of axial involvement. For each patient, the researchers calculated the BASDAI and ASDAS and correlated those with the patients’ and their physicians’ rating of disease.
The BASDAI includes patient rating of six aspects of disease: fatigue, total back pain, pain and swelling of peripheral joints, pain at entheseal sites, severity of morning stiffness, and duration of morning stiffness. The ASDAS involves only three of those factors: total back pain, pain and swelling of peripheral joints, and duration of morning stiffness. All patients gave a global assessment of their disease activity and were examined by a rheumatologist who gave a global assessment of disease activity as well.
Both the patient and physician global ratings are given on a scale of 0-10 with 10 being the most severe disease. Any patient with either a patient or physician global assessment score on either scale equal to or above 6 was considered to have highly active disease.
Both the BASDAI and ASDAS correlated well with disease activity, which is not surprising given that both consist largely of patient-derived information, the investigators said. Physician global assessment correlated less well with BASDAI and ASDAS.
Both scores were able to discriminate between high and low disease activity, an important function in that the scores are used to guide treatment decisions.
The addition of the CRP and ESR components to the ASDAS score showed poor correlation with both patient and physician ratings of disease activity. "While CRP showed only marginally significant and weakly positive correlation with patient or physician global scores, ESR did not show any significant correlation with either of those scores," the authors noted.
In a logistic regression analysis, both scores discriminated well between high and low disease activity. "As expected, the scores showed better discrimination when the definition of the disease activity was based on patient- rather than physician-derived scores," the authors wrote.
Because the scores are similarly accurate, the authors endorsed the BASDAI score on the basis of its relative simplicity. "The ASDAS score did not improve discriminative ability compared with BASDAI," they wrote. “Therefore, because BASDAI is easier to calculate, it may be more practical for clinical use in patients with axial psoriatic arthritis."
Disclosures: The study was funded by the University of Toronto Psoriatic Arthritis Program. The authors said they had no conflicts of interest.