Fatigue is common in myositis and is associated with disease activity

Fatigue is a prevalent and debilitating symptom frequently reported by patients with idiopathic inflammatory myopathies (IIM). This study investigated the reliability, validity and responsiveness of fatigue in myositis, along with its correlation with disease activity.

Adults with IIM were enrolled in a prospective observational study. Myositis core set measures and functional measures were collected at baseline, 3 months and 6 months, while patient-oriented outcomes were assessed monthly. Fatigue was evaluated using the energy-fatigue average component of the Short Form (SF)-36, and a 10 cm Visual Analog Scale (VAS).

Fifty patients (60 % females, 94 % Caucasian) with a mean age of 51.6 ± 14.9 years were enrolled. The majority of patients reported moderate to severe fatigue (67 % based on fatigue VAS and 52 % through the energy-fatigue average). Both fatigue measures showed strong test-retest reliability. Moderate to strong baseline association, along with a longitudinal correlation, was demonstrated between fatigue and various myositis outcome measures, encompassing both muscle and extra muscular disease, physician global assessment, pain, physical function, and quality of life measures. Fatigue significantly improved with improvement in myositis disease activity as assessed by 2016 ACR/EULAR response criteria as well as physician and patient-reported assessments of change in disease activity.

Fatigue is common in myositis, and demonstrates favorable psychometric properties including reliability, validity and responsiveness. Fatigue improves in conjunction with improvement in disease activity and should be regarded as an integral component of disease activity in both clinical trials and practice.