Evidence Supports Content Validity of Patient-Reported Outcome Measures in Inflammatory Myositis

Light micrograph of polymyositis
Light micrograph of polymyositis
Researchers investigated the content validity of patient-reported outcome measures in patients with idiopathic inflammatory myopathies.

Several patient-reported outcome measures (PROMs) were found to be adequate for the assessment of relevant symptoms in patients with idiopathic inflammatory myopathies (IIM), according to study results published in Seminars in Arthritis and Rheumatism.

Polymyositis, dermatomyositis, antisynthetase syndrome, and immune-mediated necrotizing myopathy are all classified as IIM, characterized by significant muscle weakness. As limited data are available regarding patients’ experiences with characterization of symptoms and disease burden, the current study was aimed at describing several PROMs for the assessment of symptoms in adult patients with IIM. 

The Outcome Measures in Rheumatology (OMERACT) Myositis Working Group selected 7 PROM instruments, based on inputs from a focus group and prior survey data, which prioritized the symptoms of adults with IIM. These instruments focused on several domains, including pain, fatigue, physical function, and physical activity. Participants completed face-to-face or phone interviews, based on their preference, to evaluate content validity of several candidate PROM instruments. Furthermore, the researchers determined whether patients’ muscle symptoms could be captured by the other 4 domains (fatigue, pain, physical activity, and physical function). 

The study sample included 20 adults (mean age, 59±12 years; 70% women) with a physician-confirmed diagnosis of IIM who were randomly selected between June 2019 and August 2019 from the Johns Hopkins Myositis Center in Baltimore, Maryland. Overall, the study included 11 responders for pain instruments, 12 for fatigue instruments, 10 for physical function, 10 for physical activity instruments, and 9 for muscle instruments. 

The majority of patients felt that each of the instruments used were clear and easy to understand, could be easily and efficiently completed, and could be used to assess its relevant domain in patients with IIM. Two-thirds of patients (66%) felt that muscle symptoms could be captured by the other 4 domains.

Although myositis has traditionally been considered a painless condition, patients felt that their pain had a significant effect on many aspects of their life. All patients who completed the pain survey (n=11), regardless of whether they had pain, felt that pain-related questions could be important to patients with pain. 

The majority of patients who completed the fatigue survey reported that they had tiredness and extreme exhaustion and strongly supported the need for instruments to assess fatigue. Participants also expressed support for all items on the survey to assess physical function; almost all participants responded that they had difficulty performing many activities and that their physical activity was limited compared to before the onset of IIM symptoms. 

“We provided evidence to support adequate content validity for several PROMs. Further research is needed to determine whether ‘muscle symptoms’ warrant a separate domain,” the researchers concluded. 


Esfandiary T, Park JK, Alexanderson H, et al. Assessing the content validity of patient-reported outcome measures in adult myositis: A report from the OMERACT myositis working group. Semin Arthritis Rheum. 2020;17;50(5):943-948.