Relationship of cancerrelated fatigue with sideeffects and symptoms of disease and treatment

There is fairly consistent evidence from studies of varying methodological quality that fatigue is related to many of the symptoms that accompany the experience of cancer and its treatment (Smets et al. 1993; Winningham et al. 1994; Nail and Winnigham 1995; Richardson 1995a). Symptoms linked with fatigue in the patient with cancer include pain, nausea, dyspnoea, and sleep disturbances. Table 2.3 lists these symptoms and a selection of the correlation coefficients reported in the literature. This highlights that the extent of the evidence is far from plentiful. Correlations between fatigue and other symptoms have only been assessed in a limited number of studies and the strength of these is inconsistent. This is not surprising as there is little similarity in the operational definitions adopted when measuring these symptoms, or in the context in which they are being assessed. However, based on the existing evidence, a degree of convergence is demonstrated. Because it is not wise to infer causation from data such as these, it is unclear whether such symptoms predispose the individual to fatigue, are consequences of it, or are simply concomitant symptoms.

Our understanding of what accounts for fatigue in patients with cancer has been supplemented by the opinions of patients themselves (see Chapters 5 and 6). These have been documented in a number of studies of both a qualitative and quantitative,

Table 2.3 Selected symptoms and reported correlations with fatigue

Symptom

Correlation coefficient

Authors

Pain

0.41

Miaskowski and Lee (1999)

0.36

Smets et al. (1998b)

0.24

Morant (1996)

0.31

Richardson (1995b)

0.48

Blesch et al. (1991)

Nausea

0.31

Richardson (1995b)

0.39

Irvine et al. (1994)

0.58

Jamar (1989)

Dyspnoea

0.41

Irvine et al. (1994)

Sleep disturbance

0.54

Miaskowski and Lee (1999)

0.41

Smets et al. (1998b)

0.40

Morant (1996)

0.43

Richardson (1995b)

0.31

Irvine et al. (1994)

and prospective and retrospective nature (Piper 1989; Pearce and Richardson 1996; Richardson and Ream 1996; Ream and Richardson 1997). In these studies patients consistently identify symptoms such as nausea, pain, and breathlessness as provoking increased feelings of fatigue, and, as a converse to this, that the relief of such symptoms often alleviates fatigue.

When designing future studies, researchers interested in uncovering the true picture of the relationship between fatigue and other symptoms associated with cancer need to acknowledge the dynamic nature of symptom expression and the manner in which symptoms are subject to change over time. Energy should be devoted to tracking symptoms across time and their relative position to each other in terms of quality, duration, distress, and intensity, as well as their subsequent influence on functional, cognitive, and physical performance. Dodd (1999) has recently raised the issue that it is likely that new methodologies/techniques will be needed in order to track symptoms across time, and we would add to this that a greater degree of rigour should be applied when selecting the timing of symptom assessments. Studies which have been carefully constructed to evaluate the pattern of symptoms which occur in discrete clusters now need to progress so that, for example, it is possible to discern which of the symptoms occurs first, and which followed. Miaskowski and Lee's (1999) study has made an important contribution in this respect.

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