An Explorative Study on Physiological and Neurophysiological Determinants of Fatigue in Cancer Survivors

Fatigue after curative treatment for cancer is a severe and invalidating problem. 20-40% of disease-free cancer patients mention fatigue as a frequent complaint, impairing quality of life. In search for (neuro)physiological factors determining fatigue, our centre has recently demonstrated the presence of morphological differences in the brains of non-cancer patients with the chronic fatigue syndrome (CFS) compared with healthy volunteers. Both in patients with CFS and in fatigued patients with neuromuscular diseases we showed that fatigue has a central neurophysiological component (so-called central activation failure). Others have shown that chronic fatigue is associated with altered brain metabolism. Studies with proton MR spectroscopy (1H MRS) have demonstrated a higher choline to creatine ratio in the brains of chronically fatigued patients. This suggests increased cell membrane turnover. Also reduced levels of N-acetylaspartate-creatine ratio (NAA/Cr) in the right hippocampus have been observed in these patients, which suggests a decrease in functional axons. Finally, elevated ventricular lactate was observed, which suggests changes in brain glucose metabolism. Actigraphy has shown that actual physical activity in fatigued cancer survivors is decreased compared to healthy controls. It is not known whether physical deconditioning originated during the actual cancer treatment is the reason why these patients are still less active. Until now no other (neuro)physiological factors have been identified explaining fatigue in cancer survivors. Recently we have shown that Cognitive Behaviour Therapy (CBT) especially designed for fatigued cancer patients is an effective treatment.

Aim: To identify and measure (neuro)physiological factors of fatigue in fatigued cancer survivors and to determine the role of these factors in the maintaining of fatigue. The identification of (neuro)physiological factors of persistent fatigue can help to improve the diagnostics of fatigue, predict therapy outcome and facilitate other treatment options. Finally, if (neuro)physiological characteristics of fatigue can be influenced by CBT it will enhance our understanding of the mechanism causing fatigue.

Research questions: 1) What are characteristic (neuro)physiological factors of fatigue in disease-free cancer patients? 2) To which degree can these factors be influenced by Cognitive Behaviour Therapy?

Design: In this explorative study fatigued disease-free cancer patients (n=57), who finished treatment for cancer at least one year and maximally ten years ago, will be approached for this study and asked for informed consent. They will be compared to age and sex matched non-fatigued patients (n=21). First, a base-line assessment will take place, which includes magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) to assess brain morphology and brain metabolites, respectively. To assess peripheral and central fatigue a two-minute endurance test will be administered at maximal voluntary (isometric) contraction (MVC). During the test changes in EMG and force indicate peripheral fatigue, while central fatigue is studied by the twitch interpolation technique. A maximal exercise test will be performed to assess physical fitness and deconditioning. At baseline patients will also be given an actometer which will register daily activity during two weeks. Further, the actometer will register daily activity up to five days after the maximal exercise test. Finally, at baseline patients will fill out a standardized questionnaire, including the Checklist Individual Strength and a self-observation list to assess fatigue severity. Then, the fatigued patients start immediately with Cognitive Behaviour Therapy (CBT). At the end of the therapy, after 6 months, a second assessment will take place in this group of patients. The assessment consists of the same measurements as at baseline. The results will be compared with the baseline situation to analyze the effect of CBT on the (neuro)physiological parameters.

Relevance of this study: Fatigue long after treatment for cancer is a frequently occurring problem, which has important consequences for quality of life in these patients. Identification of characteristic (neuro)physiological factors of fatigue in disease-free cancer patients may not only serve a theoretical understanding of this invalidating condition, but may also provide an objective biological marker that could support the diagnosis and follow-up of treatment. The identification of (neuro)physiological factors which play a role in fatigue after cancer may aid in the early recognition of patients who are at risk for developing fatigue and may lead to early intervention and/or different treatment strategies.