Are cancer pain and depression interdependent? A systematic review.

OBJECTIVE: Pain and depression are common in cancer patients. As these are both highly prevalent, the issue of a possible interdependent association has been raised. The aim of this systematic review was to examine the available literature and explore whether there is any evidence to support a causal relationship between cancer pain and depression. METHODS: An extensive literature search was undertaken. The following databases were searched electronically: Medline (1950-2007), Embase (1988-2007), CINAHL (1982-2007) and the Cochrane Database of Systematic Reviews (Issue 2 2007). The initial literature search revealed 892 articles. Following initial screening 41 articles were independently reviewed in detail. Fourteen articles were eligible for inclusion. RESULTS: The mean prevalence of both depression and pain was 36.5% (range 22.1-49.0). In 9 out of 14 studies a statistically significant association was demonstrated between pain and depression. Pain intensity positively correlated with depression (P<0.05). Items such as 'worst pain' and 'enjoyment of life' (on the Brief Pain Inventory) correlated significantly with depression. When using the McGill Pain Questionnaire, depressed patients used more affective pain descriptors. It was also shown that the longer the duration of pain, the higher the risk of depression. CONCLUSIONS: Pain and depression are highly prevalent in cancer patients; however, there have been no appropriately designed studies to examine a causal relationship. Although associations exist, the evidence available is not sufficient to support an interdependent relationship between pain and depression. A suitably designed longitudinal study to examine causality would be a relevant step in the research agenda.