The development of a modified Psoriatic Arthritis Disease Activity Score (mPASDAS) using SF-12 as a measure of quality of life.

OBJECTIVE: The Psoriatic Arthritis Disease Activity Score (PASDAS) is a composite measure of psoriatic arthritis (PsA) disease activity. The length of its patient-reported components raises concern about questionnaire burden. The PASDAS includes the SF-36 measure. We investigated the agreement between PASDAS and a modified PASDAS (mPASDAS) which substituted the SF-36 with the shortened SF-12.

METHODS: 100 patients meeting CASPAR criteria for PsA were consecutively recruited. All PASDAS required variables were collected. The 12 item responses for SF-12 were extracted from the SF-36 questionnaire. The PASDAS and mPASDAS were calculated using the SF-36 and SF-12 scores, respectively. A Bland-Altman plot of the mean differences in PASDAS and mPASDAS scores was generated to evaluate agreement. Construct validity was assessed by examining correlations of PASDAS and mPASDAS with the Health Assessment Questionnaire (HAQ), Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-fatigue), EQ5D (health-related quality of life) and pain scores. The kappa statistic was used to measure agreement between disease activity states as determined by the two scores.

RESULTS: The mean (sd) PASDAS and mPASDAS score was 3.29 (1.39) and 3.24 (1.27), respectively. The correlation between the two was 0.998 (p-value <0.0001) and mean difference (95%CI) was -0.05 (-0.07, -0.03). Construct validity was found, with near identical correlations of PASDAS and mPASDAS with each of the external health measures. Misclassification rate with mPASDAS was only 6%. The weighted kappa was 0.90 (95% CI: 0.82 to 0.97).

CONCLUSION: The mPASDAS may replace PASDAS in disease activity assessment given the excellent agreement, validity and low misclassification rate. This article is protected by copyright. All rights reserved.