Dutch ischemic stroke mortality drops, but incidence holds steady

European researchers have demonstrated a significant decline in ischemic stroke mortality in all age and sex classifications from 1980 to 2000; however, incidence of stroke was stable or may have increased slightly between 1997 and 2005. These results were published online Dec. 4 in Stroke

Using population registry data linked to hospital admission records from the Netherlands, Ilonca Vaartjes, PhD, of University Medical Center Utrecht, the Netherlands, and colleagues constructed a cohort of patients who were first admitted to the hospital with a diagnosis of ischemic stroke between 1997 and 2005. Examining this cohort against death records, the researchers were able to calculate age and sex-specific mortality at 30 days and one year after admission.

Vaartjes et al observed that 30-day mortality decreased overall from 1980 until 2010, “with some attenuation of the decline during the 1990s” among men aged 74 and younger. Since 2000, there has been a steep decline in 30-day mortality among all groups except women aged 75 to 86. The decline is most marked in men aged 65 to 84 and women aged 35 to 74.

One-year mortality showed the same pattern, with a decline overall between 1980 and 2010 in all age and sex groups except men aged 85 to 94. The groups with the biggest decline in one-year mortality were women aged 35 to 84 and men aged 65 to 84.

In contrast, there was no decline, and may have been a slight increase, in incidence of IS between 1997 and 2005. In 1997 the incidence of IS was 65 per 100,000 patients in those aged 35-64, compared with 78 in 2005; 410 in patients aged 65-74 in 1997, compared with 401 in 2005; 917 in patients aged 75-84 in 1997, compared with 936 in 2005; and 1,659 in patients aged 85-94 in 1997, compared with 1,831 in 2005.

The researchers noted that the attenuation in declining mortality in the Netherlands in the 1990s has been observed in other Western countries, including the U.S. They pointed to increases in diabetes and obesity during that period as possible explanations. As to the rapid decline in mortality since the turn of the millennium, the authors credited increases in healthcare use in the Netherlands, the number of cardiovascular procedures, the number of surgical procedures and medication use as possible explanations for the steep decline. In addition, the introduction of thrombolytic therapy and the establishment of stroke units contributed to the improvement of ischemic stroke outcomes, the authors asserted.

As to the steady rate of ischemic stroke incidence, the authors suggested that improvements in diagnosing stroke, especially minor stroke, may have a role. But they also cited increases in stroke risk factors. “Age-sex specific data on changes in risk factors in the Netherlands since 2000 are limited but suggest an unfavorable increase in both blood pressure and diabetes mellitus,” they wrote.  

The authors listed the long time frame (30 years) and the large population examined as strengths of the study. Limitations included an inability to distinguish severe strokes from minor strokes through the hospital discharge register data, and the possibility that some recurrent strokes were mischaracterized as first-time events because the researchers did not have access to hospital admission data prior to 1995. In addition, people who suffered non-fatal ischemic stroke who were not hospitalized were not included in the study, resulting in an under-reporting of ischemic stroke.