Excess mortality remains unchanged for idiopathic inflammatory myositis
Despite advancements in the treatments for rheumatic diseases, early mortality rates associated with idiopathic inflammatory myositis have not improved in recent years, according to data presented at the EULAR 2020 E-Congress.
“Prior estimates of mortality vary widely, from 23% to 73%,” Kristin M. D’Silva, MD, of the department of rheumatology at Massachusetts General Hospital, said in her presentation. “Recent trends in [idiopathic inflammatory myositis] mortality are unknown.”
D’Silva and colleagues aimed to determine whether premature mortality rates associated with this condition have improved over time.
A search of The Health Improvement Network (THIN) in the U.K. yielded data for case patients and controls ranging in age from 18 to 89 years.
Patients met Read diagnosis code criteria for dermatomyositis or polymyositis, and each patient was matched with as many as 10 controls based on age, sex, birth year and year of entry into the THIN database. An early cohort included 355 patients diagnosed between 1999 and 2006, along with 3,182 matched controls, while a late cohort included 369 patients diagnosed during 2007-2014, and 3,551 controls.
“On average, the age in all of the groups was 58 years,” D’Silva said. “Sixty-two percent of subjects were female.”
Results showed a clear excess of mortality among patients compared with controls. In the early cohort, there were 57.4 deaths per 1,000 person-years among patients with idiopathic inflammatory myopathy, compared with 15.2 deaths per 1,000 person-years for controls. In the late cohort, those rates were 43.2 for the patient population and 14.1 for controls.
This trend persisted in a multivariate analysis that accounted for age, sex, BMI, smoking, alcohol consumption, entry year into the THIN database, general practitioner visits, comorbidities and medication use. Mortality risk was higher among patients compared with controls in both the early cohort (HR = 2.73; 95% CI, 1.85-4.03) and the late cohort (HR = 2.61; 95% CI, 1.75-3.89; Pinteraction = .63). D’Silva noted that this was “a non-significant difference.”
Other findings from the multivariate analysis demonstrated absolute mortality differences of 36.6 (95% CI, 20.4-52.8) deaths per 1,000 person-years in the early cohort and 25.8 (95% CI, 13.7-37.9) deaths per 1,000 person-years in the late cohort (Pinteraction = .24). “This difference was also not statistically significant,” D’Silva said.
D’Silva concluded that an excess mortality risk for patients with idiopathic inflammatory myopathy that is more than 2.5 times higher than the general population is consistent with previous data sets.
“Our results show that there is no significant improvement in excess mortality over time, in contrast to trends seen in other rheumatic diseases, such as rheumatoid arthritis,” she said. “Further studies are needed to examine the reasons for this persistent mortality gap.”