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

Abstract

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.