Measuring physical function in psoriatic arthritis: comparing the Multi-Dimensional Health Assessment Questionnaire to the Health Assessment Questionnaire Disability Index.

OBJECTIVE: To compare physical function scales of the Multi-Dimensional Health Assessment Questionnaire (MDHAQ) to the Health Assessment Questionnaire Disability Index (HAQDI) in patients with psoriatic arthritis (PsA), and examine whether either questionnaire is less prone to 'floor effects'. METHODS: Data were collected prospectively from 2018 to 2019 across three UK hospitals. All patients completed physical function scales within the MDHAQ and HAQDI 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. RESULTS: 210 patients completed the clinic visit; one withdrew consent thus 209 were analysed. 60.0% were male, with mean age of 51.7 years and median disease duration of 7 years. In clinic, median MDHAQ and HAQDI including/excluding aids scores were 0.30, 0.50 and 0.50 respectively. Although the median score for HAQDI is higher than MDHAQ, the difference between the two mostly lies within 1.96 standard deviations from the mean suggesting good agreement. The ICCs demonstrated excellent test-retest reliability for both HAQ questionnaires.Similar numbers of patients scored '0' on the MDHAQ and HAQDI including/excluding aids (48, 47, and 49 respectively). Using a score of ≤0.5 as a cut-off for minor functional impairment, 23 patients had a MDHAQ ≤0.5 when their HAQDI including aids >0.5. Conversely, 4 patients had a MDHAQ > 0.5 when the HAQDI including aids ≤0.5. CONCLUSION: Both HAQ questionnaires appear to be similar in detecting floor effects in patients with PsA.