Background/Purpose: Pain remains a significant yet understudied aspect of idiopathic inflammatory myopathies (IIMs), considerably reducing quality of life despite advancements in immunomodulatory therapies. Information obtained from self-reported patients’ lived experiences would underscore the crucial information in improving their life quality.

Methods: We analyzed self-reported pain data within a global IIMs dataset that represent 103 countries [1]. This study used patient-experience pain visual analogue scale (VAS) with scores ranging from 0-10 and stratified the participants into mild (VAS ≤3) and moderate-severe (VAS >3) pain groups [2,3]. Socio-demographic characteristics, disease construct (type of IIM, treatment, comorbidities), and psychological construct (mental health comorbidities) were compared between groups-IIMs, RMDs, nRAIDs, and HCs. Basic multimorbidity (BM) was defined as the presence of two or more non-autoimmune comorbidities, while complex multimorbidity (CM) was defined as the presence of three or more such conditions affecting three or more different body systems. Descriptive statistics were calculated; appropriate parametric and non-parametric tests were used for comparison between groups and multivariable logistic regression was used to determine the predictors of moderate-severe pain (R studio version 2024.12.1).

Results: Among 7,847 respondents (4,709 disease controls), 1,045 (13.3%) had IIM: dermatomyositis (26.1%), overlap myositis (OM, 24.3%), inclusion body myositis (IBM, 23.4%), polymyositis (PM, 13.4%), anti-synthetase syndrome (ASyS, 6.8%), and necrotizing myopathies (IMNM, 5.6%) (Figure 1). IIMs exhibited higher pain intensity (median VAS 3.0, 1.0-5.0) than nRAIDs (1.0, 0.0-4.0) and HCs (0.0, 0.0-2.0), p< 0.01, but lower than rheumatoid arthritis (4.0, 2.0-6.0), psoriatic arthritis (4.0, 2.0-7.0), and Sjögren’s disease (4.0, 2.0-7.0), p< 0.01. (Figure 2).Overlap myositis had the highest pain levels (4.0, 2.0-6.0), while inclusion body myositis had the lowest (2.0, 0.0-4.0). Middle-aged patients (40-60 years) reported more pain than older groups. Pain primarily affected large joints (43%) and leg muscles (36.5%).Female IIM patients reported higher pain scores than males (3.0, 1.0-5.0 vs. 2.0, 1.0-5.0). Moderate-severe pain (reported by 42.7%) was significantly associated with higher fatigue, worse physical function, and poorer quality of life across all domains (p< 0.001).Significant predictors of moderate-severe pain included: overlap myositis (odds ratio, OR=2.38), arthritis (OR=2.78), mental health comorbidities (OR=2.25), and basic comorbidities (OR=1.44). Asian (OR=0.23) and Caucasian (OR=0.49) patients had lower odds of severe pain (Figure 3).

Conclusion: Pain represents a substantial burden in IIMs, particularly in overlap myositis. The bimodal distribution in IIM suggests heterogeneous pain mechanisms. Strong associations between pain intensity and reduced quality of life highlight the importance of comprehensive pain management. Multi-faceted interventions addressing identified predictors could significantly improve outcomes in this challenging disease group.

Figure 1: Table showing patient characteristics

Continuous variables described as mean ± standard deviation, or categories as number (%). Other comorbidities: chronic liver disease, chronic kidney disease, COPD, and stroke. Other mental health comorbidities: bipolar disorder, eating disorders, schizophrenia, attention deficit hyperactivity disorder, post- traumatic stress disorder, and substance use disorder.

Figure 2. 2A: Map showing participant responses across the world . 2B: Heat map showing pain intensity among different RMDs , IIM subtypes , nRAIDs and healthy controls, stratified by age groups and gender. 2C: Violin plot showing pain intensity across different participant groups. 2D: Violin plot showing pain intensity in different IIM subtypes. 2E: Violin plots showing pain intensity in different patient groups with associated comorbidities. *denotes p < 0.05

Figure 3: Forest plot showing predictors of moderate to severe pain (Pain VAS>3) in patients with IIM. *denotes p < 0.05.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/pain-in-idiopathic-inflammatory-myopathies-a-global-study-of-patient-experience/