Ethnic Differences in Ischemic Stroke Risk

A study conducted in Baltimore has suggested that African Americans under age 50 have a 61% higher likelihood of having a lacunar stroke than European Americans, and that hypertension represents a modifiable risk factor that may be involved. 

“While ethnicity, age, and sex are major non-modifiable risk factors for stroke, the modifiable risk factors remain a critical intervention point for physicians working to reduce future stroke risk,” wrote lead author John Cole, MD, and colleagues at the University of Maryland.

The study was published online in BMC Neurology.

Young onset stroke before age 50 accounts for 10-15% of all strokes, and its incidence may be increasing, according to background information in the article. The effects of young onset stroke can be devastating, resulting in more years of life affected by disability, decreased productivity, and increased family burden. 

Studies have suggested higher frequencies of ischemic stroke and differences in age-related stroke mortality among young African Americans compared to European Americans. Reasons for these differences include higher prevalence and severity of stroke risk factors, lower socioeconomic status, and biological differences between African Americans and European Americans.

In the population-based study, researchers used discharge surveillance data drawn from 59 hospitals in the Baltimore-Washington area to identify cases of first ischemic stroke in individuals aged 15-49 (n=950; 441 female, 509 male, mean age 40 years). Researchers also identified cases via direct referral from neurologists. Cases came from three different studies: the Stroke Prevention in Young Women-1 study (1992-1996), the Stroke Prevention in Young Women-2 study (2001-2003), and the Stroke Prevention in Young Men study (2003-2007).

Researchers collected data on age, sex, and ethnicity using standardized interviews. Patients or proxies self-reported stroke risk factors (hypertension and smoking). Two vascular neurologists evaluated stroke subtypes using the Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria: lacunar (small vessel), large vessel (atherosclerotic), cardioembolic, other determined etiology, and unknown etiology.

Key results for individual TOAST subtypes vs. all other subtypes combined:

• African Americans had 61% higher likelihood of lacunar stroke compared to European Americans (OR = 1.61; 95 % CI = 1.12–2.32; P = 0.011) (analyses controlled for age and sex).

• Hypertension (analyses controlled for sex, ethnicity, and age):

♦ Double the likelihood of lacunar stroke (OR = 2.03; 95 % CI = 1.38–2.98; P = 0.0003)

♦ 1.7 times higher likelihood of larger artery stroke (OR = 1.70; 95 % CI = 1.01–2.88; P = 0.048)

♦ Hypertension may have mediated the increased risk for lacunar stroke in African Americans.

• People <40 years vs. those >40 (analyses controlled for sex and ethnicity):

♦ 1.62 times higher likelihood of cardioembolic stroke (OR = 1.62; 95 % CI = 1.15–2.27; P = 0.006)

• People >40 years vs. those <40 (analyses controlled for sex and ethnicity):

♦ 2.97 times higher likelihood of lacunar stroke (OR = 2.97; 95 % CI = 1.82–4.86; P <0.0001)

♦ 2.77 times higher likelihood of large artery stroke (OR = 2.77; 95 % CI = 1.39–5.55; P = 0.004)

• Current smokers had 79% higher likelihood of large artery stroke, compared to non-smokers (OR = 1.79; 95 % CI = 1.08–2.98; P = 0.024).

Small sample size in several TOAST subgroups may have limited the analysis because other traditional stroke risk factors like diabetes and past MI could not be explored. In addition, data on hyperlipidemia was inadequate, so the study did not include this variable. Finally, the study could not analyze other stroke etiologies like dissection and hypercoagulable states, as well as other risk factors seen in younger populations, like drug abuse and complications of pregnancy.

Nevertheless, the authors emphasized the critical importance of smoking cessation, and pointed out that hypertension may increase the risk for young onset ischemic stroke in ethnically specific ways.

“These findings may help clarify mechanisms of stroke in young adults, which may be partially driven by ethnic differences in the onset of early traditional stroke risk factors,” they concluded, “Awareness of these associations may improve a physician’s ability to recognize predisposing risk factors for a specific subtype of ischemic stroke within an individual, thereby indicating a differing emphasis on primary and secondary stroke prevention and infer on the workup after a stroke has occurred.”

Take-home Points

• A Baltimore study found African Americans are at increased risk for young onset lacunar stroke, and that hypertension may play a role.

• Hypertension increases the likelihood of lacunar and large artery stroke.

• People under age 40 have a higher likelihood of cardioembolic stroke, while those age 40 and over have a higher likelihood of lacunar and large artery stroke.

• Smoking increases the risk of large artery stroke.

Reference: Trivedi MM, et al. Ethnic differences in ischemic stroke subtypes in young-onset stroke: the Stroke Prevention in Young Adults Study. BMC Neurol. 2015 Oct 29;15(1):221.