Degenerative Disorders Account for Rising Share of US Neurological Disease Deaths

By Lisa Rappaport

June 26, 2020

(Reuters Health) - Neurological disease mortality rates in the U.S. are similar to what they were two decades ago, but over time the main cause of these deaths has shifted from cerebrovascular diseases to Alzheimer's dementia and other neurodegenerative disorders, a U.S. study finds.

Researchers calculated age-adjusted mortality rates per 100,000 using records from 1999 to 2017 in the U.S. Centers for Disease Control and Prevention Wide-ranging Online Data for Epidemiologic Research (WONDER) database. Mortality rates were standardized to the 2000 U.S. population and calculated for all neurological diseases as well as for the cerebrovascular, neoplastic, neurodegenerative, and other neurological causes categories.

Overall neurological age adjusted annual mortality rates declined from 98.6 per 100,000 in 1999 to 84.2 per 100,000 in 2013, but then rebounded to 98.6 per 100,000 in 2017, an increase of 4.1 per year, the authors report in JAMA Neurology.

During the study period, mortality rates for cerebrovascular diseases dropped from 61.6 to 37.6 per 100,000. Over this same time, mortality rates for neurodegenerative disorders climbed from 16.9 to 36.8 per 100,000.

"Since 1999 we've had some amazing new treatments for cerebrovascular disease, and while we can't prove causality with this study, it is likely that these innovations are responsible for the decreased mortality rates that we're seeing," said study coauthor Dr. Eric Karl Oermann, Chief Resident of Neurological Surgery at the Mount Sinai Health System in New York City.

"Unfortunately, new treatments for neurodegenerative diseases have not been as successful, and with an aging population, we are likely seeing more neurodegenerative disease - namely, Alzheimer's disease - than before," Dr. Oermann said by email.

The South was the only U.S. region to see growth in overall neurological disease mortality rates, with an increase from 103.0 to 109.3 per 100,000.

Although cerebrovascular disease mortality declined from 65.9 to 42.1 per 100,000 over the course of the study in the South, the region's rates remained consistently highest relative to other regions.

Additional studies are needed to examine how differences in access to care, or racial and socioeconomic disparities might influence regional mortality rates, the study team notes.

Shifts in how deaths are categorized on death certificates may also have influenced the study results, said Theo Vos, a professor at the Institute for Health Metrics and Evaluation at the University of Washington in Seattle who wasn't involved in the study. Over time, it's become more common for dementia to be listed as the cause of death, Vos, who wasn't involved in the study, said by email.

"The increases in deaths rates are so large that this cannot possibly fit with what we know about changes in the occurrence of dementia," Vos said. "This is a clear example of measurement bias."

Mortality rates also don't tell the whole story of disease burden, said Dr. Abolfazl Avan of Mashhad University of Medical Sciences in Iran.

"While mortality due to cerebrovascular disease is decreasing, their burden is increasing, because those individuals suffering from cerebrovascular disease remain alive but in a poor condition," Dr. Avan, who wasn't involved in the study, said by email. "Thus, the rate of chronic condition death and burden should be analyzed simultaneously."

Death rates from neurological disease will also likely accelerate with an aging population and rising prevalence of these disorders in the population, Dr. Avan added.

"As the population is growing older, we need to allocate resources to controlling modifiable risk factors to prevent or decrease the mortality and burden of both cerebrovascular and neurodegenerative diseases," Dr. Avan said.

SOURCE: JAMA Neurology, online June 22, 2020.