Thursday 30 May 2013

Silent strokes, a quiet killer

By K Ranga Krishnan, Published TODAY, 29 May 2013 

It is not uncommon to see the elderly steadily retreating from activities such as reading, walking or going to play mahjong, losing interest in activities they previously enjoyed and becoming detached even when their grandchildren come to visit.

If you ask them whether anything is wrong and if they are well, one usually gets responses such as “I am tired” or “Nothing is wrong, I just don’t feel like it” or, even more often heard, “I am just feeling old”.

We all tire a little more easily as we get older, due to natural ageing, but sometimes, these symptoms suggest other problems that could be more serious.

There are many reasons an older individual might feel this way. It could be that they have a medical problem, perhaps heart disease or thyroid disease.

But one very common and under-recognised cause for such responses is depression. It gets missed often because we attribute the lack of interest and lethargy to ageing, that is, just getting old. We miss that something is wrong.

There are many reasons why this should be recognised, evaluated and treated.

One reason is that the presence of lethargy, loss of interest and depression may, in fact, be a sign of major medical problems.

In the elderly, this form of depression is frequently connected to the occurrence of silent strokes. We usually picture a stroke patient as having paralysis of the arm or leg, but this is seen only when the stroke affects the part of the brain that controls movement.

Can strokes be silent? Yes, if they affect parts of the brain that are not connected to movement or sensation. The word “silent” is used here simply to refer to the fact that the person is oblivious a stroke has occurred as he or she does not have motor, speech or sensory problems.

There is now overwhelming evidence that such depression, lack of interest and lethargy could be due to silent strokes in the brain. Numerous people are ignorant of this fact, yet millions will have a stroke each year and not know they have it. In fact, silent strokes are very widespread compared to the strokes that paralyse an individual.

Silent strokes are very rare in the young but their frequency increases with age. They are not new; it is just that the greater accessibility of high-resolution magnetic resonance imaging (MRI) scans of the brain means more of these strokes are now being detected when scans are being done for other reasons.

My interest in this started when the first MRI scanners were just becoming available. I was interested in studying the elderly, especially those who were depressed. When we started scanning elderly individuals, we noted bright spots on their brain MRI scans. We, and others, did not know what they were.

In fact, when they were first seen they were called unidentified bright objects (UBOs).

Studies over the next few years showed that many of these UBOs were strokes. In fact, some represented damage to the brain where the tissue was destroyed, leaving a hole, or lacune, in the brain.

Many people are literally walking around with these silent strokes but blissfully unaware that they have had a stroke. The MRI-identified stroke leads to few symptoms or symptoms that are not attributed by patients or physicians as caused by a stroke.

The range of symptoms includes memory problems, sadness, apathy, urinary problems and falls. These symptoms are often fuzzy and, hence, are frequently missed.

Over time, they cause balance problems and falls in the elderly and the loss of bladder control.

These strokes typically occur in parts of the brain — often the front of the brain — that depend on a solitary source of blood supply without other alternative sources. The regions of the brain that suffer such strokes do not control movement or process sensation but are implicated with thinking and mood regulation. Hence, a silent stroke is more likely to be missed.

These preliminary findings led to several large studies in the United States and Europe. The population studies showed that, as people age, silent strokes in the brain become more common. In fact, they are very widespread over the age of 70.

A few studies in Asians, particularly those conducted in Japan, point to even higher rates of occurrence of these types of strokes. Worldwide, about 10 per cent of healthy middle-aged people and up to 40 to 50 per cent are thought to have had silent strokes without being aware of it.

But these strokes are not benign. They are indicators of something more sinister. Silent strokes are caused by elevated blood pressure, smoking, diabetes mellitus and narrowing of the main blood vessels to the brain.

The risk increases with age.

Genes also play a key role in silent strokes. There is a rare genetic disease that causes the blood vessels in the brain to narrow and thus lead to reducing the blood supply and subsequently stopping the blood flow leading to a stroke. Individuals with this disease get silent strokes at a very young age.


These strokes are frequently associated with memory impairment and lead to a form of dementia — vascular dementia. This type of dementia is more widespread among Asians. It also leads to depression and increases the probability of future strokes and death.

The term “vascular depression” has been used to describe depression found in such individuals. These strokes are associated with poor response to anti-depressants and the persistence or worsening of depressive symptoms over time.

The depression and dementia worsen if the injury to the brain increases.

High blood pressure, diabetes and high cholesterol become more prevalent with age and very evident during middle age. Numerous investigations in the US and Europe as well as Japan have reported that the presence of these risk factors in mid-life is related to silent strokes 20 years later.

The time to prevent silent strokes is in middle age.

Controlling blood pressure, cholesterol and blood sugar in mid-life, as well as not smoking, may be the key to preventing silent strokes and dementia, particularly among us.

Detection, treatment and prevention could greatly benefit all of us. Take the time to get tested and treated now before it is too late.

K Ranga Krishnan is the Dean of the Duke-NUS Graduate Medical School Singapore. He is also an international expert in treating depression and other brain disorders of the elderly.

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