Survey Identifies Four Pain Phenotypes in Idiopathic Inflammatory Myopathies

Researchers used an anonymous electronic survey to characterize pain heterogeneity in patients with self-reported idiopathic inflammatory myopathies (IIM) and pain attributed to myositis. The analysis included 426 participants and incorporated demographic, disease, and pain information alongside the Fibromyalgia Survey Questionnaire. Latent class analysis used pain distribution, pain pattern, the difference between pain during a myositis flare and current pain, and disease duration.

Four classes emerged: proximal arm- and leg-predominant pain with the lowest persistent pain; diffuse axial and proximal limb-predominant pain; diffuse axial and distal leg-predominant pain; and widespread axial and extremity pain with the highest persistent pain. Post hoc analyses showed that the first class primarily included participants with earlier IIM and a lower rate of fibromyalgia. The two intermediate classes had intermediate fibromyalgia symptom burden, whereas the widespread-pain class had the highest pain intensity and fibromyalgia burden.

The authors interpret these patterns as spanning localized, disease-related nociceptive pain to widespread, fibromyalgia-like nociplastic pain. The findings may guide mechanistic research and future phenotype-directed management, but they do not establish pain mechanisms or treatment effectiveness. Interpretation is limited by self-reported diagnoses and pain attribution; the supplied abstract provides no class sizes or quantitative between-class comparisons.