Measuring Physical Function in Psoriatic Arthritis: Comparing the Multidimensional Health Assessment Questionnaire to the Health Assessment Questionnaire-Disability Index.

To compare physical function scales of the Multidimensional Health Assessment Questionnaire (MDHAQ) with that of the Health Assessment Questionnaire-Disability Index (HAQ-DI) in patients with psoriatic arthritis (PsA), and to examine whether either questionnaire is less prone to "floor effects." Data were collected prospectively from 2018 to 2019 across 3 UK hospitals. All patients completed physical function scales within the MDHAQ and HAQ-DI in a single clinic visit. Agreement was assessed using medians and the Bland-Altman method. Intraclass correlation coefficients (ICCs) were used to assess test-retest reliability. Two hundred ten patients completed the clinic visit; 1 withdrew consent. Thus, 209 were analyzed. Sixty percent were male, with mean age of 51.7 years and median disease duration of 7 years. In clinic, median MDHAQ and HAQ-DI including/excluding aids scores were 0.30, 0.50, and 0.50 respectively. Although the median score for HAQ-DI was higher than for MDHAQ, the difference between the 2 scores was mostly within 1.96 SDs from the mean, suggesting good agreement. The ICCs demonstrated excellent test-retest reliability for both the MDHAQ and HAQ-DI. Similar numbers of patients scored 0 on the MDHAQ and HAQ-DI including/excluding aids (48, 47, and 49, respectively). Using a score of ≤ 0.5 as a cutoff for minor functional impairment, 23 patients had a MDHAQ ≤ 0.5 when their HAQ-DI including aids was > 0.5. Conversely, 4 patients had a MDHAQ > 0.5 when the HAQ-DI including aids was ≤ 0.5. Both the MDHAQ and HAQ-DI appear to be similar in detecting floor effects in patients with PsA.

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