Infections, respiratory tract disease linked to elevated risk of IIM
Individuals with a history of infection or respiratory tract disease are at greater risk of developing idiopathic inflammatory myopathy (IIM), suggesting that the triggering of the immune system may occur outside the skeletal muscle, according to a case–control study.
Using data from Swedish nationwide registers, researchers identified 957 patients with IIM (mean age 59 years; 57 percent female). Each patient was matched with non-IIM controls by age, sex and place of residence (n=9,476). Data on outpatient visits and hospitalizations for infection or respiratory disease prior to IIM diagnosis were also drawn from the registers.
Conditional logistic regression models were applied to test the association between infection or respiratory tract disease and future risk of developing IIM. Sensitivity analyses were also performed by changing the exposure definition, controlling for previous healthcare consumption and excluding individuals with connective tissue disease, IIM lung phenotype or IIM-associated cancer.
Results revealed that preceding infections occurred more frequently in the IIM group than in the control group (13 vs 9 percent) and were associated with an increased risk of IIM (odds ratio [OR], 1.5; 95 percent CI, 1.2 to 1.9). Specifically, gastrointestinal and respiratory tract infections were linked to a heightened IIM risk, whereas cutaneous infections were not.
Likewise, preceding respiratory tract disease was more common in the IIM group than in the control group (10 vs 4 percent), increasing the risk of developing IIM by more than twofold (OR, 2.3; 1.8 to 3.0). Both upper and lower respiratory tract diseases were associated with an increased risk of IIM.
Researchers noted that variations in exposure and outcome definitions had no significant effect on the results.
The present data suggest that external triggers of immunomodulation could be part of the aetiology of IIM, with the events possibly presenting years before the clinical manifestations of IIM become evident, researchers said.