SAN ANTONIO — As many as four in 10 people referred to a clinic with signs of a “ministroke” may have subtle cognitive damage that standard tests miss, a new study shows.
The findings, reported by Canadian researchers February 24 at the International Stroke Conference in San Antonio, Texas, suggest that after suffering the ministrokes many patients lose some ability to process abstract thoughts, reason things out and make quick calculations — what doctors call “executive function.”
While full-blown strokes cause a clear loss of cognitive function, most often due to a blood vessel blockage in the brain that shows up on an MRI or CT scan, ministrokes are caused by smaller obstructions. They result in more subtle deficits that are less likely to be detected by brain scans or even by patients themselves. Some scientists consider the term ministroke a misnomer, preferring the technical term transient ischemic attack, while others use the terms interchangeably.
The symptoms of a ministroke or a full-blown one might start out the same, with numbness in the face or extremities, confusion, vision problems, dizziness or headache. But in a ministroke, these symptoms wane after minutes or hours.
In the new study, researchers tested 140 such patients in whom symptoms subsided within 24 hours, indicating they had ministrokes instead of full-blown ones. They gave the subjects a test of cognitive acuity that is routinely given to patients who show up at a clinic or hospital with signs of a stroke. Known as the Mini-Mental Status Exam, the test quickly gauges 30 cognitive functions including short-term recall, attention span, spatial recognition and executive function.
MMSE testing found only 5 percent to be cognitively impaired. But when researchers gave the patients four other tests specifically designed to gauge executive function, the number of impaired individuals ranged from 13 to 40 percent depending on the test, said Michael Harnadek, a neuropsychologist at the London Health Sciences Center in Canada, who presented the data.
The patients were 67 years old on average. In the general population, executive function impairment shows up in about 7 percent of people this age, he said.
The tests of executive function included tasks like drawing a clock with the hands pointing to a specific time and putting digits in numerical order. Loss of these skills suggests a corresponding deterioration in everyday tasks such as taking phone messages and keeping track of car keys.
“We used to attribute this to aging, but we now know that this isn’t normal aging,” Harnadek said. “It’s these cognitive difficulties.”
Just having a ministroke places a person at heightened risk of a full-blown stroke, said Lee Schwamm, a vascular neurologist at Harvard Medical School and Massachusetts General Hospital in Boston.
Schwamm pointed out that the same risk factors that increase a patient’s risk of having