Using brain scans, scientists in the US have uncovered physiological evidence for "chemo brain", a common and often debilitating side effect of cancer chemotherapy treatment that patients often describe as a "mental fog". With the help of positron emission tomography combined with computed tomography (PET/CT), the team found that following chemotherapy, areas of the brain involved with planning and decision-making use less energy.

Rachel A Lagos, a diagnostic radiology resident at the West Virginia University School of Medicine and West Virginia University Hospitals, and colleagues, presented their findings at the 98th scientific assembly and annual meeting of the Radiological Society of North America (RSNA) in Chicago on 27 November.

In a statement to the press, Lagos talks about "chemo brain":

"The chemo brain phenomenon is described as 'mental fog' and 'loss of coping skills' by patients who receive chemotherapy."

"Because this is such a common patient complaint, healthcare providers have generically referred to its occurrence as 'chemo brain' for more than two decades," she explains.

However, while the complaint may be common, scientists have struggled to pinpoint its causes. Some have had success with MRI (magnetic resonance imaging) scans, and identified some small changes in brain volume after chemotherapy, but nothing definite.

So Lagos and colleagues decided to try a different approach: instead of examining what the brain looks like after chemo, they examined changes to its metabolism, or how it uses energy, using a PET/CT combination.

Lagos says when they looked at the results, they were surprised at how "obvious" the changes were, and asserts:

"Chemo brain phenomenon is more than a feeling. It is not depression. It is a change in brain function observable on PET/CT brain imaging."

For their study, the team examined PET/CT scans of 128 patients who had had chemotherapy for breast cancer.

With the help of special software, they were able to pinpoint differences in brain metabolism before and after chemo. They then correlated these with patient history and data from neurologic exams and chemo treatments.

The analysis reveals a statistically significant link between reductions in regional brain metabolism and symptoms of chemo brain.

Lagos says their findings show "there are specific areas of the brain that use less energy following chemotherapy".

"These brain areas are the ones known to be responsible for planning and prioritizing," she adds.

The researchers hope their PET/CT approach will be used to diagnose chemo brain so patients receive help sooner.

There is already evidence that changes to diet, use of exercise, massage and counseling help patients with chemo brain. For instance, Lagos relates a study where women reported losing their ability to prepare family meals. After receiving help in the form of written and planned menus, the women were able to shop for and prepare the meals successfully.

The team hopes more studies will now be done to improve support for patients with chemo brain.

Lagos says a prospective study that starts looking at patients earlier, at the time of their cancer diagnosis, could identify how brain chemistry changes during chemo, which could lead to improved treatment or even prevention of chemo brain.

Written by Catharine Paddock PhD