Pain and depression in patients with cancer

Although the existence of a relationship between depression and pain in patients with cancer has been known for many years, the influence of one upon the other is still poorly understood. It has been thought that depressed individuals complain of pain more because of their psychiatric illness. Evidence from two studies indicate that pain may induce clinical depression.

In the first study, the authors examined both current and lifetime psychiatric diagnoses among patients with cancer who had high and low pain symptoms to examine the strength of the relationship between depression and cancer pain. The sample consisted of 72 women and 24 men, with 39 women and 9 men in the high pain group, and 33 women and 15 men in the low pain group. In the second study, 35 patients with metastatic carcinoma of the breast were examined for pain intensity and frequency and mood disturbance.

The prevalence of depressive disorders of all types was found to be significantly higher in the high pain than in the low pain group across measures, 33 versus 13% (chi-square [degrees of freedom = 1] = 5.90, P < 0.05). Furthermore, there was a significantly higher history of major depression in the low pain group than in the high pain group (chi-square [degrees of freedom = 1] = 3.86, P < 0.05). Also, in comparison with patients in the low pain group, patients in the high pain group were significantly more anxious and emotionally distressed. In the second study, pain intensity correlated significantly with fatigue, vigor, and total mood disturbance, and pain frequency correlated significantly with fatigue, vigor, and depression.

This study confirms the high concomitant occurrence of pain and psychiatric morbidity and suggests that pain may play a causal role in producing depression.