Evaluation of physical function in patients with inflammatory myopathies using the health assessment questionnaire-II...

Idiopathic inflammatory myopathies (IIM) are autoimmune diseases characterized by chronic muscle inflammation leading to impaired physical function and strength. Despite the importance of functional assessment, only few validated tools exist for this population. The Health Assessment Questionnaire-II (HAQ-II), a streamlined 10-item version of the HAQ, may provide an efficient instrument. This study aimed to evaluate the measurement properties of HAQ-II in patients with IIM.

Adults with IIM enrolled in Forward Databank (2005-2023) with available data on HAQ-II were included. Patients completed HAQ-II along with assessments of disease activity, pain, fatigue, quality of life (SF-36), and comorbidities. Internal consistency of HAQ-II was assessed using Cronbach's α. Floor and ceiling effects, discriminant and construct validity (based on a priori hypotheses), and responsiveness (via linear mixed models adjusted for age, sex, and obesity) were evaluated.

A total of 192 IIM patients (mean age 54.8 years; 79.3% female) were included. HAQ-II demonstrated high internal consistency (α = 0.93), no significant floor or ceiling effects. Discriminant validity was supported by significant score differences across groups stratified by SF-36 physical function, pain, fatigue, and disease activity (all p < 0.0001). Fifteen of 17 a priori hypotheses for construct validity were met. Longitudinal changes in HAQ-II scores were significantly associated with changes in pain, fatigue, global disease activity, and SF-36 physical component scores.

HAQ-II demonstrated high internal consistency, no significant floor or ceiling effects, adequate validity and responsiveness for assessing physical function in patients with IIM and could be appropriate for both clinical and research settings.