Science

Silent strokes often undiagnosed

As many as one in 12 people over 60 may experience a stroke without knowing it, according to an Australian study that also found high blood pressure to be a significant risk factor.

As many as one in 12 people over 60 may experience a stroke without knowing it, an Australian study suggests.

The research, led by Dr. Perminder Sachdev of the University of New South Wales, also found high blood pressure to be a significant risk factor. 

'We see blood pressure as one of the risk factors and it shouldn't be, because high blood pressure is entirely treatable.'— Dr. Perminder Sachdev

Silent strokes occur when blood flow is blocked in one of the arteries leading to areas deep within the brain, which is typically unnoticed by the sufferer. 

Sachdev and colleagues scanned the brains of nearly 500 healthy 60- to 64-year-olds using magnetic resonance imaging (MRI). They found 7.8 per cent of the volunteers had areas of the brain damaged by stroke, despite them being unaware that anything had occurred.

When the team later scanned the same volunteers four years later, they found an additional 1.6 per cent had experienced silent strokes.

The results of the study appear in Tuesday's issue of the journal Neurology.

  Common signs of stroke are: 

       
  • Sudden weakness or numbness of the arms, legs or face, especially on one side.
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  • Quick onset of blurred vision in one or both eyes.
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  • Difficulty walking, dizziness, or loss of balance or co-ordination.
  •    
  • Sudden confusion or trouble speaking.
  •    
  • Sudden severe headache with no known cause.

Sachdev, a professor of neuropsychiatry, says silent strokes may explain many of the cliché symptoms of old age such as forgetfulness, slowing down and becoming easily confused.

"[The strokes] probably have a cumulative effect. If they are very small then the brain has enough reserves to be able to cope with them and not show any abnormalities in function. But as they are increasing then the brain's reserve is depleted and you start seeing abnormalities," he says.

Sachdev says silent strokes can result in slowing of motor function, a reduction in information-processing speed and less efficient memory for detail.

He says many of the sufferers of the stroke are not aware their cognitive performance has declined.

Blood-pressure risk

Sachdev says people with high blood pressure were 60 per cent more likely to have silent strokes than those with normal blood pressure. He says people with another type of small brain damage called white matter hyperintensities were almost five times more likely to experience the tiny strokes.

Professor Richard Lindley, board member of Australia's National Stroke Foundation (NSF), says the study supports previous research into the relationship between stroke and blood pressure.

"The study suggests that high blood pressure is important, and this fits in with what we know about clinical stroke — high blood pressure being the most important single risk factor," he says.

Lindley says the NSF is also interested in the link between silent stroke and old age-related problems.

"The findings  … suggest that some problems in old age will be due to vascular disease in the brain, despite a lack of a stroke history. The challenge is to prove that we can prevent these types of lesions."

Sachdev recommends older Australians have their blood pressure tested regularly and seek treatment if it is up.

"We see blood pressure as one of the risk factors and it shouldn't be, because high blood pressure is entirely treatable."

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