Infections in Polymyositis and Dermatomyositis: Analysis of 192 Cases

Objectives: To estimate the incidence, characteristics and predictors of infections in patients with PM and DM.

Methods: The medical records of 192 PM/DM patients followed up in a tertiary teaching medical centre from 1999 to 2008 were retrospectively reviewed.

Results: Seventy-six episodes of major infection, defined as infections requiring>1 week of treatment with anti-microbial agents, occurred in 53 (27.6%) patients, and 15 (7.8%) patients had two or more episodes. The incidence rate of major infections was 11.1 episodes per 100 patient-years in PM/DM patients. Aspiration pneumonia [n (%)=16 (21.1)] was the leading cause of major infections, followed by opportunistic infection [n (%)=14 (18.4)]. A variety of pathogens were isolated, mainly including Staphylococcus aureus, Klebsiella, Escherichia coli, Salmonella and Mycobacterium. Overall patient survival rates were 85.0% at 1 year, 78.0% at 5 years and 78.0% at 10 years. However, after one episode of major infection, survival rates decreased to 84.7% at 30 days and 68.3% at 1 year. Multivariate analysis indicated that independent predictors of major infection were age>45 years at PM/DM onset [odds ratio (OR) 5.26; 95% CI 2.01, 13.77; P=0.001], presence of arthritis/arthalgia (OR 2.59; 95% CI 1.12, 6.02; P=0.027), co-present interstitial lung disease (OR 7.24; 95% CI 2.67, 19.65; P<0.001), current use of AZA (OR 6.07; 95% CI 2.39, 15.42; P<0.001) or IVIG (OR 6.33; 95% CI 1.50, 26.77; P=0.012).

Conclusions: This study underlines the high frequency of major infections in PM/DM, which is significantly detrimental to patient survival rates. Close follow-up of PM/DM patients with risk factors for developing major infections is mandatory.