Psychobiological markers in coexisting pain and depression: toward a unified theory.

Psychological and biological variables were examined in two groups of patients with both depression and pain. The relationship of these variables to severity of pain and to pain threshold was examined in a nontreatment evaluation group (N = 25), and their relationship to relief of pain and depression was examined n a doxepin-treated group (N = 16). Eighty-seven percent of the treatment group experienced some pain relief, and 56% experienced complete relief. In the nontreatment group, anxiety as measured on the Zung Anxiety Scale, depression as measured on the Hamilton Depression Scale, and urinary 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) were all found to correlate significantly and positively with severity of pain as rated on the McGill Pain Questionnaire. Each of these variables was related to different dimensions of the pain experience as measured by the McGill-Melzack Pain subscales. Only anxiety correlated significantly with pain threshold. In the treatment group final pain relief was positively correlated with initial MHPG and anxiety and with improvement in depression. A theory unifying biological, psychological, and clinical experimental pain data is presented.