Infection is not rare in patients with idiopathic inflammatory myopathies

Objective To assess the prevalence and characteristics of infections in patients with idiopathic inflammatory myopathies (IIM) and analyse risk factors for infection using clinical presentation and biochemical findings of IIM. Methods Retrospective review of the medical records of patients with IIM followed up in a single medical centre from January 2008 to January 2018. Results Of the 779 patients with IIM, 215 (27.6%) suffered from infections. The prevalence of infection in dermatomyositis (DM) (29.8%) was more than polymyositis (PM) (18.5%). The lung was the most common infection site (66.5%). Multivariate analyses demonstrated that methylprednisolone pulse (MP) (OR=3.22; 95% CI=1.60-6.48; p=0.001), age of onset >50 years (OR=1.02; 95% CI=1.00-1.03; p=0.011), anti-melanoma differentiation-associated gene 5 (MDA5) antibody (OR=1.93; 95% CI=1.20-3.11; p=0.007), lymphocyte count <1200/mm(3) (OR=2.85; 95% CI=1.89-4.30; p<0.001), and interstitial lung diseases (ILD) (OR=2.03; 95% CI=1.30-3.71; p=0.002) are independent risk factors for infection. Survival analysis demonstrated that the three-year survival rate in the infection group was lower than the no-infection group (75.3% vs. 94.7%, p<0.001). Conclusion Among hospitalised individuals with IIM, infection is frequent and the leading cause of mortality. The anti-MDA5 antibody, lymphopenia, ILD, old age, and treatment with MP are contributing factors in the development of infections in patients with IIM.