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The foggy world of chemobrain


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The foggy world of chemobrain

TheStar.com - Science - The foggy world of chemobrain

Many cancer patients experience a kind of post-chemotherapy fuzziness that can be long-term and debilitating. Researchers are still struggling to explain why

November 03, 2007

Hannah Hoag

special to the star

Can't remember. Can't concentrate. Can't even find the keys.

These are all things we experience from time to time, but many people with cancer find they develop a cloudiness during chemotherapy they just can't shake.

Because patients associate the onset of their problems with the treatment, this mental fog has been dubbed chemobrain.

But it's not yet clear to researchers that chemotherapy is to blame. And while this mild cognitive impairment is not a new complaint, it is only in the last decade that researchers have begun to study it.

"There are still some people who would doubt that there is an effect," says Ian Tannock, a medical oncologist at the Princess Margaret Hospital, who studies the cognitive effects of chemotherapy.

Many patients receiving chemotherapy will experience a mild mental fuzziness during treatment, says Timothy Ahles, a clinical psychologist at Memorial Sloan-Kettering Cancer Center in New York City.

It can often be chalked up to fatigue, anemia, sedating drugs and sleep difficulties.

For most it's a mild annoyance that clears up. For others it is a debilitating condition that can last for years after their last cancer treatment.

"It's transient for most people. It lasts for a while and then it gets better," says Tannock.

"But there is a very low incidence of people who appear to suffer profoundly from this for many years after, such that it affects their lifestyle."

The effects can be subtle – they're not nearly as dramatic as Alzheimer's or head trauma. They can also be difficult to measure.

Neuropsychological tests that measure memory and speed have long been considered the gold standard.

"The problem is, these tests have been designed to assess people with fairly severe brain pathologies – strokes, brain tumours or head trauma in a car accident. They're not great at picking up these subtle changes," says Ahles.

Often these people achieve scores within the normal range, although prior to their cancer they may have scored higher.

"The brightest and the best and those most likely to have a high cognitive demand in their lives may be the most likely to complain that there is something wrong," says Barbara Collins, a neuropsychologist at the Ottawa Hospital.

Multi-tasking becomes almost impossible. Juggling ringing phones, beeping emails and colleagues knocking at the door can become overwhelming.

"In many cases, these neurocognitive side effects are the primary reason cancer survivors do not return to work," says Collins, who spoke on the problem yesterday at a downtown conference for young women living with breast cancer.

Most oncologists and neuropsychologists agree the likely offenders include high doses of chemotherapy, the combination of chemotherapy and hormone therapies like tamoxifen, or the early menopause women in their '30s and '40s often experience with treatment.

Chemotherapy can mess with ovarian function and estrogen levels, triggering rapid and premature menopause in young women.

"The brain is rich in estrogen receptors," says Collins. "There is a role for female sex hormones in memory and cognition."

Most of the work on chemobrain has been done on breast cancer patients, but the phenomenon has been found in other cancer patients as well, including those with small-cell lung cancer, colorectal cancer and lymphoma.

Recently, a number of small studies have used brain scans to look at the effects of chemotherapy on brain function.

One study showed breast cancer survivors who had been treated with chemotherapy and tamoxifen had sluggish metabolism in the part of the brain that controls short-term memory. Another, using magnetic resonance imaging (MRI), found the brain structure of areas involved in attention span and visual memory had been altered after chemotherapy. Three years after treatment, the changes were no longer obvious, suggesting the brain can recover.

In September, Ahles co-authored a study that compared the cognitive functioning of a breast cancer survivor who had been treated with chemotherapy with her twin sister who did not have cancer.

Although their test results were similar, the survivor had many more cognitive complaints than her twin, and functional MRI studies, which measure brain activity, showed the twin who had had chemotherapy had to activate different areas of her brain to perform the tests.

"People perceive a cognitive change, but they may be able to perform at normal levels because they can compensate," says Ahles. "It feels different and it may explain why when people are under stress or have multiple demands or deadlines that they are unable to compensate and the difficulties emerge."

The mechanisms behind chemobrain remain a bit of a mystery. There is new evidence that chemical signals called cytokines produced by the immune system may attack brain neurons.

Researchers are also looking at whether genetic variations and chemotherapy-induced DNA damage might play a role in these cognitive changes.

Until cancer researchers find the cause of chemobrain, cancer survivors are finding ways to cope with their memory changes.

They use electronic calendars to record appointments, buy key chains that beep when you press a button, and track their memory problems in small diaries that can be tucked into a pocket or bag. Others find doing crossword puzzles and solving Sudoku squares stimulate their thinking.

Athough there are very early studies looking at the effects stimulant medications have on chemobrain, the results are far from conclusive and many people cannot tolerate the effects.

But perhaps the most effective intervention is avoiding situations that are likely to cause confusion.

"It might be best to not get yourself into a bind where there are multiple deadlines, time pressures and a lot of stress," says Ahles. "It's many of the things we should all be doing anyway."

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