OBJECTIVE: The interplay between dysphagia, cancer, and mortality in idiopathic inflammatory myopathies (IIM) has not been carefully studied. The aim of this study was to investigate possible effect modification of cancer on the association between dysphagia and mortality in early IIM. METHODS: A multi-center cohort of 230 adult IIM patients with dysphagia assessment within 6 months of disease onset was assembled. Crude mortality rates in IIM patients exposed or not to dysphagia were estimated for the 5-year period following cohort entry. To explore possible effect modification of cancer on the association between dysphagia and mortality, adjusted Cox models stratified on cancer status were performed as well as an interaction model. RESULTS: Mortality rates per 100 person-years for IIM patients exposed to dysphagia were 2.3 (95 %CI 1.0 to 4.5) in those without cancer compared to 33.3 (95 %CI 16.6 to 59.5) in those with cancer. In stratified Cox models, the main effect of dysphagia was HR 0.5 (95 %CI 0.2 to 1.5) in non-cancer and 3.1 (95 %CI 1.0 to 10.2) in cancer patients. In the interaction model, the combination of dysphagia and cancer yielded a HR of 6.4 (1.2 to 35.1). CONCLUSION: In this IIM cohort, dysphagia in non-cancer patients was not associated with increased mortality, while it was in presence of cancer, supporting effect modification of cancer on the association between dysphagia and mortality. This suggests that IIM patients with and without cancer differ and separate analyses for the two groups should be conducted when the outcome of interest is mortality.

Center for Rheumatology and Spine Diseases Copenhagen University Hospital Rigshospitalet Copenhagen Denmark; Department of Rheumatology Odense University Hospital Odense Denmark

Department of Mathematics and Statistics McGill University Montreal Canada

Department of Rheumatology Research Support Services Oslo University Hospital Oslo Norway

Division of Rheumatology Department of Medicine Solna Karolinska Institutet Stockholm Sweden; Department of Gastro Dermatology and Rheumatology Theme Inflammation and Aging Karolinska University Hospital Stockholm Sweden

Division of Rheumatology Department of Medicine Solna Karolinska Institutet Stockholm Sweden; Department of Gastro Dermatology and Rheumatology Theme Inflammation and Aging Karolinska University Hospital Stockholm Sweden; Center for Molecular Medicine Karolinska Institutet Stockholm Sweden

Division of Rheumatology Department of Medicine Solna Karolinska Institutet Stockholm Sweden; Division of Clinical Epidemiology Department of Medicine Solna Karolinska University Hospital Karolinska Institute Stockholm Sweden; Department of Gastro Dermatology and Rheumatology Theme Inflammation and Aging Karolinska University Hospital Stockholm Sweden

Division of Rheumatology Department of Medicine Solna Karolinska Institutet Stockholm Sweden; Division of Clinical Epidemiology Department of Medicine Solna Karolinska University Hospital Karolinska Institute Stockholm Sweden; Jewish General Hospital and Lady Davis Institute Montreal Canada; Department of Medicine McGill University Montreal Canada

Institute of Rheumatology and Department of Rheumatology 1st Medical Faculty Charles University Prague Czech Republic

Jewish General Hospital and Lady Davis Institute Montreal Canada; Department of Medicine McGill University Montreal Canada

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