Fatigue. Measures and relation to pain.

Fatigue describes reduced capacity to sustain force or power output, reduced capacity to perform multiple tasks over time and simply a subjective experience of feeling exhausted, tired, weak or having lack of energy. Pain and fatigue have several components in common, such as being subjective, prevalent in most patients with cancer and caused by multiple factors of both a physical and psychological nature. In order to explore the relationship between fatigue and pain, data from five studies were used: two random samples from the Norwegian population (n=2323 and n=1965), Hodgkin's disease survivors (n=459), palliative care patients (n=434) and patients with bone metastases (n=94). All patients had completed one or more of the following instruments: EORTC QLQ-C30, SF-36 and/or Fatigue Questionnaire. The level of fatigue was much higher in the two palliative care populations (54.4 and 63.2) as compared to the normal population samples (25.0). Patients with bone metastases had significantly more pain (72.0) than the patients in the palliative care trial (47.4) and norms (20.5). In the two palliative care and bone metastases populations fatigue was almost unchanged over time, while pain was reduced. In the palliative care population a high level of fatigue (80.3) and pain (57.8) was reported 0-1 month before death. The relationship between pain, fatigue and the health-related quality of life domains should be explored in more detail, especially in follow-up studies in order to assess possible changes over time. In addition, the validity of the existing instruments measuring fatigue should be investigated for use in patients with advanced disease and short life expectancy.