Although the incidence of stroke is increasing steadily among young adults, the incidence of acute myocardial infarction (AMI) remains stable, a new analysis suggests.
This finding raises the question of whether cardiovascular risk factors are the main cause of the increasing incidence of stroke among younger people, said the researchers.
“It has been a mystery why the number of strokes in young adults has been growing,” Michelle Hu Leppert, MD, assistant professor of neurology at the University of Colorado School of Medicine in Aurora, told Medscape Medical News. “This is a trend seen worldwide.”
Leppert presented the findings at the European Stroke Organization-World Stroke Organization (ESO-WSO) Conference 2020.
The incidence of stroke has risen among young adults even as it has declined markedly in older adults. In 2017, a study by George and colleagues showed that discharge diagnoses for cardiovascular risk factors among young adults who had been hospitalized for stroke had increased over time.
Improvements in diagnostic coding might explain the observation, but some suggested that the prevalence of cardiovascular risk factors in young adults may be increasing.
Stroke and AMI may be considered analogous diseases because they share many cardiovascular risk factors, Leppert said. The researchers hypothesized that if cardiovascular risk factors were causing increased stroke incidence among young adults, the same trend should hold for AMI incidence in this population.
To test the hypothesis, they retrospectively analyzed a 10% random sample of patients included in PharMetrics Legacy, a nationally representative claims database. They identified participants between the ages of 15 and 44 years who were enrolled continuously for at least 6 months between 2001 and 2014. The primary outcomes were incident stroke and incident AMI, which the researchers defined as the first hospital admission with ischemic stroke or AMI as the primary diagnosis.
Leppert and colleagues included approximately 3 million patients in the analysis. The data sample included 1720 index strokes and 1848 index AMIs. The researchers categorized participants into three age groups: 15 to 24 years, 25 to 34 years, and 35 to 44 years.
Among patients aged 25 to 34 years, the incidence of stroke increased by 48% over 10 years. Among patients aged 35 to 44 years, stroke incidence increased by 28% over 10 years.
The investigators also examined the population by gender. Stroke incidence increased by 34% per 10 years (P = .03) in men between ages 35 and 44 years. Stroke incidence also increased by 59% per 10 years (P = .02) in women between ages 25 and 34 years.
The investigators found no statistically significant change, however, in the rate of incident AMI for men and women in any of the age groups.
The findings of Leppert and colleagues are comparable with those of the National Inpatient Sample, which showed a 40% increase in stroke hospitalizations over 10 years in young adults, they note.
Noncardiovascular Risk Factors
Although AMI is generally caused by cardiovascular disease in young adults, a young adult may have a stroke for one of many reasons, including noncardiovascular risk factors, said Leppert.
“We can think of the portion of strokes in young adults resulting from cardiovascular risk factors to be analogous to AMIs in young adults. The most popular belief prior to our study was that the piece of the pie representing strokes resulting from cardiovascular risk factors has been getting bigger,” she said. “We were able to show in this study that this belief may not be true.”
Rather, the proportion of strokes resulting from noncardiovascular risk factors may be increasing, said Leppert. It is also possible that improved detection and diagnosis of stroke have contributed to an apparent increase in incidence. Diagnostic testing and MRI have become widespread, as has public knowledge of the symptoms of stroke.
Stroke is less common among younger than older adults, but its consequences may be long-lasting.
“Our goal right now is to better define just what the contributions of these cardiovascular and noncardiovascular risk factors are and exactly what they are,” she said. “We are especially interested in how these risk factors contribute to stroke differently in young men and women. I think that by having a fuller understanding, we can start to target our primary and secondary prevention efforts.”
The study by Leppert and colleagues benefits from a large dataset and a longitudinal design, but it has several shortcomings as well, Jose Gutierrez, MD, MPH, Florence Irving assistant professor of neurology at Columbia University Irving Medical Center in New York City, told Medscape Medical News.
For example, the investigators used ICD-9 codes to adjudicate stroke, but this technique does not reveal stroke etiology.
“We don’t know the ethnic composition of the sample and, therefore, whether the sample may have been biased towards ethnic groups with variable rates of stroke versus AMI,” said Gutierrez, who was not involved in the study.
“Stroke is a much more heterogeneous disease than AMI, which is more often attributed to coronary atherosclerosis,” he added. “The effects of hypertension on brain arteries may cause stroke without atherosclerosis.” It thus may be inappropriate to conclude that shared risk factors are not involved in the rising stroke burden in the young because the incidence of AMI has remained stable, Gutierrez said.
“The results are a call to action to diagnose early and treat aggressive risk factors such as hypertension, diabetes, dyslipidemia, and smoking. Diverting attention to other rare causes of stroke in the young, such as hypercoagulability, HIV, dissection, etc, may distract from treating these risk factors,” he continued. Aggressive interventions targeting such risk factors have been proven to reduce the risk of stroke and may also preserve memory and decrease the risk of cognitive impairment or dementia.
Neurologists should carry out “exhaustive” investigations of stroke etiology, said Gutierrez. They should actively seek to identify traditional risk factors in younger populations and emphasize strict targets for risk-factor control.
Finally, neurologists should “establish a strong communication with primary care doctors so that they understand that keeping tight targets for risk-factor control is imperative to decrease further stroke risk and disability,” Gutierrez concluded.
The study was funded by an American Heart Association Bugher Foundation Grant and a KL2 Scholar Award from the Colorado Clinical and Translational Science Institute. Leppert and Gutierrez have reported no relevant financial relationships.
European Stroke Organization-World Stroke Organization (ESO-WSO) Conference 2020. Presented November 8, 2020.
For more Medscape Neurology news, join us on Facebook and Twitter.