Assessment of Pain Characteristics, Attribution, and Nociplasticity in Patients With Inflammatory Myopathies: An International Survey Study.

OBJECTIVE: Idiopathic inflammatory myopathies (IIMs) have historically been viewed to cause painless weakness and are therefore poorly understood. We aimed to report pain characteristics in patients with IIMs and estimate the contributions of fibromyalgia and common painful comorbidities to pain intensity. METHODS: An international electronic survey was circulated to individuals who self-reported IIMs and pain attributable to myositis. Questions included pain characteristics, perceptions of provider understanding of their pain, comorbidities, and the Fibromyalgia Survey Questionnaire. Hierarchical multiple linear regression was used to examine the contribution of fibromyalgia symptom burden and other painful comorbidities to pain intensity (0-10 visual analog scale), adjusting for age, sex, country, IIM subtype, and duration. RESULTS: A total of 552 participants (mean age 58.0 years; 81.3% female) with pain attributable to myositis were included. Mean pain intensity was 4.6 out of 10. Most participants reported pain starting near diagnosis. The most painful areas were back, neck, and upper legs. The majority reported that their pain was not well understood by their care team. Approximately 60% met the fibromyalgia criteria and reported higher, more persistent, and widespread pain. Pain intensity was the highest in overlap myositis and lowest in inclusion body myositis. Fibromyalgia symptom burden explained 20% of variance in pain intensity, whereas osteoarthritis, degenerative disc disease, and diabetic neuropathy were not significant contributors. CONCLUSION: Most patients with self-reported IIMs experience moderate, persistent pain that is not well understood by their care team. Fibromyalgia symptom burden accounted for a substantial proportion of pain variability, suggesting an important nociplastic component, though additional mechanisms likely contribute.