Background Disease Activity index for Psoriatic Arthritis (DAPSA) originally developed from patients with reactive arthritis (1). Subsequently, validation of DAPSA was also shown on psoriatic arthritis (PsA) patients (2). DAPSA includes swollen joint count (SJC) (66 joint), tender joint count (TJC) (68 joint), CRP (mg/dl), patient global assessment, and pain. However, it is well known that assessment of 28 joint is feasible than 66/68 joints especially in the rheumatoid arthritis trials.
Objectives Objective of this study was to assess construct validity and sensitivity to change of DAPSA-28 in a single center biological registry.
Methods Hacettepe University biological registry (HUR-BIO) is a single center biological registry. Since 2012, consequently all PsA patients with new started anti-TNF treatments were recorded. HUR-BIO included sex, age, PsA disease duration, education, body mass index (BMI). Before anti-TNF treatments, baseline disease activity parameters were recorded: SJC and TJC (28 joints), health assessment questionnaire (HAQ), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), Bath ankylosing spondylitis activity index (BASDAI), visual analog scale 0–100 mm (VAS) of patient's global assessment of disease activity (PGA), pain, and fatigue. Original DAPSA calculated to sum of CRP (mg/dl), pain VAS (cm), PGA VAS (cm), SJC (66 joints), and TJC (68 joints). We used 28 TJC/SJC instead of 66/68 joints for calculation of DAPSA, which called DAPSA-28. At baseline, all DAPSA items completed in 78 patients. The subsequent clinical visit recorded in 53 patients (4.6±3.0 months after baseline). Statistical analysis: Internal consistency was evaluated using Cronbach's α coefficient. Construct validity was assessed by Spearman's correlation between the DAPSA-28 scores and other measures. Sensitivity to change assessed with standardised response mean (SRM). A SRM >0.8 is considered large.
Results Overall, 58 of 78 (74.4%) were female, mean age was 43.1 (11.8) years, mean PsA duration was 6.4 (5.1) years. Mean DAPSA-28 score was 20.1 (8.1). Patients with low educational level (primary scholl 22.8 (9.6) vs high scholl 16.8 (5.7), p=0.009), and high BMI (BMI >30 kg/m2 22.4 (8.4) vs BMI <30 kg/m2 17.8 (7.2), p=0.011) had higher DAPSA-28 score. Mean of all DAPSA items were followed; PGA 5.8 (1.7), pain 6.3 (2.3), CRP 2.0 (2.8), SJC 1.9 (2.2), TJC 4.0 (3.6). DAPSA-28 domains had moderate internal consistency (Cronbach's α 0.61). Correlation of DAPSA-28 with other outcome measures followed; DAS-28 (r=0.86), TJC (r=0.78), SJC (r=0.73), PGA (r=0.48), pain VAS (r=0.47), CRP (r=0.44), fatigue VAS (r=0.38), HAQ (r=0.36), ESR (r=0.35), and BASDAI (r=0.31). DAPSA-28 had excellent SRM (1.14).
Conclusions DAPSA domains are almost universal for all kind of inflammatory arthritis. Simple sum of those domains seem valid and feasible in PsA patients. Although assessment of 66/68 joints may be rational particularly patients with distal interphalangeal involvement, it has feasibility issue. Our results demonstrated that DAPSA-28 had excellent capacity at sensitivity to change for clinical trials. Unfortunately, we could not compare DAPSA with DAPSA-28, future studies are needed for these comparison.
Ann Rheum Dis 2010;69:1441–7
Disclosure of Interest None declared