CHICAGO (Reuters) - Older adults often do not realise or may even forget they have had a stroke and may not be a reliable source of medical information, US researchers said on Monday.

Brain scans showed that while just 12 percent of seniors asked about strokes remembered having had one, nearly a third had brain damage showing they had.

The stroke itself could damage memory, and many people may also have so-called silent strokes that are never diagnosed at the time, Dr. Christiane Reitz of Columbia University Medical Center in New York and colleagues wrote in the Archives of Neurology.

"Stroke is associated with motor impairment but can also be accompanied by impairments in memory, sensation and speech or language, diminishing the ability of an individual to accurately report a history of stroke," they wrote.

The team studied magnetic resonance imaging or MRI scans of 717 people 65 or older who were covered by the federal Medicare insurance programme for the elderly. "Approximately 75 percent of strokes occur in persons older than 65 years," the researchers wrote.

The volunteers were interviewed about their health and took some basic neurological and psychological tests. Patients and their caregivers also completed a survey about stroke history, including whether they had stroke symptoms or had been told they had a stroke.

Nearly 12 percent, or 85 people, said they had. But MRI scans showed 225 people, or 30 percent, had actually suffered a stroke.

People who got it wrong were more likely to have poorer memory or language ability, or have stroke risk factors such as high blood pressure or a history of a heart attacks. Younger people in the study were more likely to get it right.

"However, it is likely that some of the strokes that were not reported were silent strokes," the researchers wrote.

The team said researchers who want to study stroke in older adults need to rely on MRI scans, and not patients, to get accurate information about stroke history.