PT  - JOURNAL ARTICLE
AU  - John Svensson
AU  - Marie Holmqvist
AU  - Ingrid E Lundberg
AU  - Elizabeth V Arkema
TI  - Infections and respiratory tract disease as risk factors for idiopathic inflammatory myopathies: a population-based case<strong>–</strong>control study
AID  - 10.1136/annrheumdis-2017-211174
DP  - 2017 Nov 01
TA  - Annals of the Rheumatic Diseases
PG  - 1803--1808
VI  - 76
IP  - 11
4099  - http://ard.bmj.com/content/76/11/1803.short
4100  - http://ard.bmj.com/content/76/11/1803.full
SO  - Ann Rheum Dis2017 Nov 01; 76
AB  - Objectives To investigate the association between infection or respiratory tract disease and future risk of developing idiopathic inflammatory myopathy (IIM).Methods A case–control study was performed using Swedish nationwide registers. Adults with newly diagnosed IIM were identified (2002–2011) from the National Patient Register (NPR) and the Swedish Rheumatology Register (n=957). Controls were matched by age, sex and place of residence (n=9476). Outpatient visits and hospitalisations preceding IIM diagnosis indicating infection or respiratory disease were identified from NPR. Conditional logistic regression models were used to calculate OR and 95% CI. Sensitivity analyses were performed by varying the exposure definition, adjusting for previous healthcare consumption and excluding individuals with connective tissue disease, IIM lung phenotype or IIM-associated cancer.Results Preceding infections were more common in IIM cases compared with controls (13% vs 9%) and were associated with an increased risk of IIM (OR 1.5, 95% CI 1.2 to 1.9). Gastrointestinal and respiratory tract infections were associated with an increased risk of IIM while cutaneous infections were not.Preceding respiratory tract disease was present in 10% of IIM cases and 4% of controls (OR 2.3, 95% CI 1.8 to 3.0). Both upper and lower respiratory tract diseases were associated with an increased risk of IIM.Variations in exposure and outcome definitions did not greatly affect the results.Conclusions Infections and respiratory tract diseases are associated with an increased risk of IIM which suggests that the triggering of the immune system may take place outside the skeletal muscle.