Datasets with only 28 joint counts available (ie, Disease Activity index for PSoriatic Arthritis [DAPSA]) can be used to calculate a modified DAPSA28 and have demonstrated validity as a  tool for patients with psoriatic arthritis (PsA), particularly those with low disease activity, according to the results of a cohort study using data derived from the Danish national quality registry DANBIO. Findings from the analysis were published in Annals of the Rheumatic Diseases.

Investigators sought to explore the psychometric performance of a modified DAPSA with the use of 28 rather than 66 swollen/68 tender joint counts (SJC/TJC). Patients with PsA from DANBIO were divided into 2 cohorts: an examination cohort (n = 3157 patients;
23,987 visits) and a validation cohort (n = 3154 patients; 24,160 visits). DAPSA28 was defined as follows: DAPSA28 = (28TJC x conversion factor1) + (28SJC x conversion factor2) + patient global (0-10VAS) + pain (0-10VAS) + C-reactive protein (CRP; mg/dL).

The estimates derived from the analysis were as follows: DAPSA28 = (28TJC x 1.6) + (28SJC x 1.6) + patient global (0-10VAS) + pain (0-10VAS) + CRP (mg/dL). Based on criterion validity, DAPSA/DAPSA28 had comparable discriminative power (DAPSA, 0.90; DAPSA28, 0.93) to differentiate between patients with high and low disease activity.

Based on correlational validity, baseline DAPSA/DAPSA28 exhibited significantly high correlation of 28-joint disease activity score with CRP levels (P <.001). Better agreement was demonstrated for low than for high disease activity. Regarding construct validity, DAPSA/DAPSA28 correlated similarly to the Health Assessment Questionnaire (P <.001). DAPSA/DAPSA28 discriminated patients reported their symptom state as acceptable vs not acceptable equally well (mean 9.1 ± 8.7/8.4 ± 8.0 and 24.2 ± 14.9/22.5 ± 13.8, respectively).


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The investigators concluded that the DAPSA28 demonstrated good criterion, correlational, and construct validity, as well as sensitivity to change. Nonetheless, the study results recommend that the original DAPSA should be preferred and that 66/68 joint counts should nonetheless be performed among patients with PsA in order to calculate DAPSA.

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Reference

Michelsen B, Sexton J, Smolen JS, et al. Can disease activity in patients with psoriatic arthritis be adequately assessed by a modified Disease Activity index for PSoriatic Arthritis (DAPSA) based on 28 joints? (published online September 20, 2018).  Ann Rheum Dis. doi: 10.1136/annrheumdis-2018-213463