, new research showed.
The findings may offer insight into the increased incidence of stroke in adults under age 45, which has more than doubled in the past 20 years in high-income countries, while incidence in those over 45 has decreased.
Investigators believe the findings are important because most conventional prevention efforts focus on traditional risk factors.
“The younger they are at the time of stroke, the more likely their stroke is due to a nontraditional risk factor,” lead author Michelle Leppert, MD, an assistant professor of neurology at the University of Colorado School of Medicine, Aurora, Colorado, said in a news release.
The findings were published online in Circulation: Cardiovascular Quality and Outcomes.
Traditional Versus Nontraditional
The researchers retrospectively analyzed 2618 stroke cases (52% female; 73% ischemic stroke) that resulted in an inpatient admission and 7827 controls, all aged 18-55 years. Data came from the Colorado All Payer Claims Database between January 2012 and April 2019. Controls were matched by age, sex, and insurance type.
Traditional risk factors were defined as being a well-established risk factor for stroke that is routinely noted during stroke prevention screenings in older adults, including hypertension, diabetes, hyperlipidemia, sleep apnea, cardiovascular disease, alcohol, substance use disorder, and obesity.
Nontraditional risk factors were defined as those that are rarely cited as a cause of stroke in older adults, including migraines, malignancy, HIV, hepatitis, thrombophilia, autoimmune disease, vasculitis, sickle cell disease, heart valve disease, renal failure, and hormonal risk factors in women, such as oral contraceptives, pregnancy, or puerperium.
Overall, traditional risk factors were more common in stroke cases, with nontraditional factors playing a smaller role. However, among adults aged 18-34 years, more strokes were associated with nontraditional than traditional risk factors in men (31% vs 25%, respectively) and in women (43% vs 33%, respectively).
Migraine, the most common nontraditional risk factor for stroke in this younger age group, was found in 20% of men (odds ratio [OR], 3.9) and 35% of women (OR, 3.3).
Other notable nontraditional risk factors included heart valve disease in both men and women (OR, 3.1 and OR, 4.2, respectively); renal failure in men (OR, 8.9); and autoimmune diseases in women (OR, 8.8).
An Underestimate?
The contribution of nontraditional risk factors declined with age. After the age of 44, they were no longer significant. Hypertension was the most important traditional risk factor and increased in contribution with age.
“There have been many studies demonstrating the association between migraines and strokes, but to our knowledge, this study may be the first to demonstrate just how much stroke risk may be attributable to migraines,” Dr. Leppert said.
Overall, women had significantly more risk factors for stroke than men. Among controls, 52% and 34% of women had at least one traditional and nontraditional risk factors, respectively, compared with 48% and 22% in men.
The total contribution of nontraditional risk factors was likely an underestimate because some such factors, including the autoimmune disorder antiphospholipid syndrome and patent foramen ovale, “lacked reliable administrative algorithms” and could not be assessed in this study, the researchers noted.
Further research on how nontraditional risk factors affect strokes could lead to better prevention.
“We need to better understand the underlying mechanisms of these nontraditional risk factors to develop targeted interventions,” Dr. Leppert said.
The study was funded by the National Institutes of Health/National Center for Advancing Translational Sciences Colorado Clinical and Translational Science Award. Dr. Leppert reports receiving an American Heart Association Career Development Grant. Other disclosures are included in the original article.
A version of this article appeared on Medscape.com.