Quality of life correlates with muscle strength in patients with dermato- or polymyositis.

The aim of this study was to compare health-related quality of life (HQoL) in adults with dermatomyositis (DM) or polymyositis (PM) with a healthy control group and to assess whether muscle strength was associated with HQoL in patients with DM or PM. A cross-sectional study was performed and included 75 patients with DM or PM and 48 healthy controls. HQoL was assessed by the Short Form 36 questionnaire (SF-36). Muscle strength of the patients was assessed using the Manual Muscle Test-8 (MMT8). Covariables and possible confounding factors were collected by validated tools. Associations were determined in multiple linear regression models. The patients had significantly lower HQoL than the control group in both the physical component summary score (PCS) and the mental component summary score (MCS). Thus, the PCS-difference between groups was 32% (p < 0.001), whereas the MCS-difference was 14% (p < 0.001). Muscle strength was associated with one domain in the patients; Physical Function (β = 1.2; 95% confidence interval 0.37 to 2.1). No statistically significant associations were found between muscle strength and HQoL in the remaining domains. Patients with DM or PM have reduced HQoL compared to healthy controls. Notably, muscle strength was associated with scores of the domain reflecting perceived physical function in patients. These findings corroborate the validity of including selected patient reported outcomes in the evaluation and monitoring of patients with DM or PM.