Inflammatory Myopathy Mortality Highest in First Year

Janis C. Kelly

August 23, 2017

Adults with idiopathic inflammatory myopathy (IIM) have a threefold higher risk for death, and that risk is highest during the first year after diagnosis, a study found.

The findings indicate clinicians should take extra care in monitoring these patients during that time, Gerd Cecilie Dobloug, MD, PhD, from the Department of Rheumatology, Oslo University Hospital, Norway, and colleagues report in an article published online August 16 in the Annals of the Rheumatic Diseases.

"Novel information from this study is that the overall mortality in IIM is highest during the first year after IIM diagnosis and then decreases, in contrast to the general population where the reversed was seen with an increased mortality rate during a >10-year follow-up period," the authors explain. "The major causes of death in patients with IIM are malignancies, diseases of the circulatory and respiratory system, all of them already during the first year after IIM diagnosis."

These findings highlight the systemic nature and frequent extramuscular manifestations of IIM, supporting the authors' call for increased monitoring of muscle strength and of heart and lung function, as well as surveillance for malignancies in patients with IIM.

The researchers used data from the Swedish National Patient Register to identify a cohort of 716 patients with newly diagnosed IIM who were matched in a 1:10 ratio to individuals from the Swedish Population Register. The IIM cohort was 55.2% women with median age of 61.4 years at the start of follow-up. Median follow-up was 4.6 years in the IIM cohort and 6.0 years in the general population.

The primary outcome was death from any cause. Secondary outcomes were cause-specific deaths such as malignant neoplasms, respiratory diseases, circulatory system diseases, and certain infections and parasitic diseases. The researchers also examined the main reasons for hospitalization during the month before death.

The analysis showed that IIM was associated with increased mortality, that mortality was highest within the first year of IIM diagnosis, and that mortality remained more than double that in the general population over the course of more than 10 years. Patients with IIM were also younger than the general population at time of death (mean age, 73 vs 79 years).

Mortality during follow-up was 31% in the IIM cohort and 12% in the general population, corresponding to a crude incidence rate of 59.9 (95% confidence interval [CI], 42.0 - 77.8) deaths/1000 person-years in patients with IIM and 19.8 (95% CI, 16.5 - 23.1) deaths/1000 person-years in the general population.

There were also sex differences in mortality, which was similar for men and women in the IIM cohort but higher in men than women in the general population.

Cumulative mortality at 1 year after diagnosis was 9% in IIM compared with 1% in the general population. Cumulative mortality at 5 years was 23% in IIM vs 8% in the general population. By 10 years, cumulative mortality was 31% vs 12%, which was not a statistically significant difference.

Main causes of death were musculoskeletal and connective tissue disease, malignancies, diseases of the circulatory system, and diseases of the respiratory system in the patients with IIM. Main causes of death in the general population were malignancies, circulatory system disease, and respiratory system diseases.

Adjusting for age, sex, residential area, birth year, and year of diagnosis gave an overall hazard ratio of 3.73 (95% CI, 3.19 - 4.37), and the increased risk applied to dermatomyositis as well as other IIMs, to all age groups, and to both men and women. The relative risk for death was highest in the youngest age group: Those younger than 53 years at diagnosis had a hazard ratio of 7.14 (95% CI, 4.06 - 12.54).

The first year after IIM diagnosis emerged as a particularly dangerous time, with increased absolute and relative risk for death, particularly for respiratory system disease and malignant neoplasms.

"There has been some discussion regarding whether there is an increased mortality in patients diagnosed with IIM in recent years, but this study leaves little doubt to this question," the authors explain.

"This study also demonstrates that the mortality is highest within the first year of IIM diagnosis, and it remains more than doubled compared with the general population throughout a follow-up of over 10 years, although the increased relative risk was not statistically significant after 10 years. After adjusting for age, sex, residential area, birth year and year of diagnosis, a >3-fold mortality risk was seen in IIM compared with the general population."

The researchers advise careful surveillance of newly diagnosed patients with IIM for cancer, lung involvement, and heart involvement, as well as careful monitoring of heart and lung function during the first year of follow-up. They write, "These comorbidities are captured both by the disease activity score, myositis disease activity tool, and the disease damage score, myositis damage index, developed by the International Myositis Assessment and Clinical studies group network, and these can be used in clinical practice for surveillance and as support tools for decision making on therapies."

The study was funded by the Swedish Research Council (Vetenskapsrådet), Research Agreement on Medical Training and Clinical Research, Karolinska Institutet, Swedish Rheumatism Association (Reumatikerförbundet), and Swedish Society of Medicine (Svenska läkaresällskapet). One coauthor reports receiving research grants from Astra-Zeneca and Bristol-Myers Squibb and has consultancies from Bristol-Myers Squibb and IDERA Pharmaceuticals. All other authors have disclosed no relevant financial relationships.

Ann Rheum Dis. Published online August 16, 2017. Abstract

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