Background/Purpose: Dermatomyositis and polymyositis (DM/PM) are chronic inflammatory muscle diseases that may cause premature death due to progressive muscle weakness, lung disease, and disease and treatment complications. Large-scale, population-based data on DM/PM mortality are scarce. We conducted a population-based study to assess mortality trends over a 24-year study period and analyzed proximate causes of death for DM/PM across the U.S.

Methods: We used the Center for Disease Control and Prevention database to obtain the numbers of DM/PM and non-DM/PM deaths. Using these death-counts and population data from the U.S. Census Bureau, we calculated age-standardized mortality rate (ASMR) per million with 95% confidence interval (CI) for DM/PM, non-DM/PM and ratio of DM/PM to non-DM/PM for each year from 1999-2022. We used joinpoint regression modeling to evaluate mortality trends. We also compared death-counts in medical facilities with those from homes or other locations. Additionally, we analyzed proximate underlying causes of death in DM/PM decedents.

Results: There were 12,882 deaths with DM/PM recorded as the underlying or a contributing cause of death and 63,547,770 non-DM/PM deaths in the U.S. from 1999 through 2022. The DM/PM-ASMR decreased from 2.4 per million in 1999 to 1.2 in 2018 at an annual percent change (APC) of -3.81 (95% CI -4.34 to -3.40; p< 0.01). This rate increased over the next 4 years to as high as 1.5 in 2021 at an APC of 5.27 (95% CI 0.97- 14.13; p< 0.01). Non-DM/PM ASMR continuously decrease as well, from 1999-2017 (APC, – 1.19 [95% CI -1.52 to -0.89], p< 0.01) but increased since then (APC, 4.44 [95% CI 2.70-7.17], p< 0.01) with the ASMR higher in 2021 than in 1999. Consequently, the ratio of DM/PM-ASMR to non-DM/PM-ASMR continuously decreased over the 24-year period at an APC of -2.56 (95% CI -2.98 to -2.19; p< 0.01). The number of deaths from DM/PM were consistently higher in medical facilities (59.1%) than at home/other places of death (40.9%). DM/PM was recorded as the underlying cause of death in 50% of all DM/PM decedents. Of the remaining 50% where DM/PM was recorded as a contributing cause of death, cancers, atherosclerosis heart disease, interstitial pulmonary disease, serious infections, and ischemic heart disease were among the top five leading underlying causes of death. Cancers and ischemic heart disease as the underlying causes of death in DM/PM steadily declined over the study period at annual percent changes of -5.51 (95% CI, -6.93 to -4.26) and -6.97 (95% CI, -8.56 to -5.67), respectively.

Conclusion: Mortality from DM/PM has shown a decreasing trend from 1999 until the start of the COVID-19 pandemic when it significantly increased, which could be directly attributed to COVID-19 as the underlying cause of death. There were disproportionately higher number of DM/PM deaths in medical facilities. Of 50% of DM/PM decedents where DM/PM is recorded as a contributing cause of deaths, cancers and ischemic heart diseases have steadily declined over the last two decades.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/dermato-polymyositis-mortality-in-u-s-population-declining-cancer-and-cardiovascular-diseases-among-the-leading-underlying-causes-of-death-over-two-decades/