More than half of the memory gap between stroke-free patients and stroke survivors may be observable before the stroke.
NEW ORLEANS—Memory declined about three times as fast in people who later had a fatal stroke as it did in control patients who did not have a stroke, according to a study presented at the 2012 International Stroke Conference. In addition, memory declined almost twice as quickly in patients who later survived a first stroke as it did in control patients.
More than half of the memory gap between people who survived a stroke and people who were stroke-free “was probably there prior to the stroke,” said M. Maria Glymour, ScD, Assistant Professor of Society, Human Development, and Health at the Harvard School of Public Health in Boston. “They were already experiencing memory losses that were quite severe,” she added.
A Diverse, National Patient Sample
Dementia and severe memory impairment are common in patients who have survived a stroke. In people with no history of stroke, memory impairment indicates an elevated risk of future stroke. “We thought that to really understand this, we needed to take a much longer-term picture and follow people over the long term to see how their memory changed before and after stroke,” said Dr. Glymour.
She and her colleagues based their study on the Health and Retirement Study cohort, which is a representative sample of US residents 50 and older as of 1998. Patients in the cohort are interviewed biennially and given a brief memory assessment, including a word list recall. Spouses assess the memory of patients who become too impaired to undergo a direct memory assessment. When a patient has a stroke, the month and year of the stroke are recorded.
Dr. Glymour and her colleagues analyzed data for 11,814 patients from 1998 through 2008. Nearly 41% of patients were male, and about 83% were white. To see how memory changed before a stroke, the investigators restricted their analysis to patients who had not had a stroke at baseline in 1998.
The study compared memory function in people who had a stroke and survived during follow-up, people who had a stroke and did not survive, and people who did not have a stroke during follow-up. The team used regression models to plot patients’ average memory change over time.
Three Patient Groups With Distinct Rates of Memory Decline
Memory declined suddenly before the onset of a stroke, according to the investigators. Stroke caused an immediate loss of memory equivalent to that observed at the end of a four-year period in stroke-free patients. Patients who survived a stroke continued to experience a decline in memory, but at a slightly faster rate than before the stroke.
The mean baseline memory score of the stroke-free patients was 2.63. In contrast, baseline memory score for patients who later survived a stroke was 1.83, and it was 1.21 for patients who later died after a stroke. The annual age-related memory decline for stroke-free patients was 0.08, compared with 0.14 for stroke survivors and 0.21 for stroke decedents.
New Questions About Stroke and Memory Decline
Dr. Glymour noted several limitations of the study, including the focus on one cognitive domain and the investigators’ lack of access to patients’ medical records and neural imaging data. But the study also had several strengths, including the large, diverse national sample, the long-term follow-up, and the ability to study impaired patients whose memory could not be assessed directly, according to Dr. Glymour.
The study raises new questions that the team plans to investigate. “We want to look next at whether there are … personal features that modify the effects of stroke and whether there are certain behaviors … that can protect you from memory decline associated with stroke,” concluded Dr. Glymour.
—Erik Greb