A prospective study of the pathophysiology and clinical characteristics of pain in a palliative medicine population.

Comprehensive pain evaluation is requisite for optimal management. Few studies have evaluated pain syndromes and adequacy of associated analgesic regimens in one population. Available studies in cancer populations have focused on ambulatory patients or hospice-type inpatients. This study was designed to evaluate multiple characteristics of pain and adequacy of therapy in a broad spectrum of patients with advanced cancer presenting to a palliative medicine service. One hundred pain patients (95 with cancer) underwent a comprehensive pain evaluation consisting of history, physical examination, review of available diagnostics, and a pain assessment tool designed for routine clinical use. Seventy-one percent of 141 evaluable patients reported pain in the month before referral. In these 100 patients, 158 distinct sites of pain were reported, with 88 percent reporting a maximum of 2. Pain due to tumor was the most common cause (68 percent), and the most common pathophysiologic mechanism, somatic (52 percent). Pain was almost equally divided between continuous (48 percent) and intermittent (52 percent). Breakthrough pain occurred in 75 percent of continuous pains. Of these, 30 percent were exclusively incidental, 26percent nonincidental, and 16 percent due to end-of-dose failure. The remainder was of mixed etiology, but almost always with an incidental component. Of intermittent pain syndromes, 61 percent were incidental. On referral, analgesic dosing was inadequate and was compounded by use of regimens that typically did not meet peer-reviewed guidelines. Comprehensive studies rigorously evaluating characteristics of pain and response to treatment are a necessary first step toward more effective treatments for difficult pain syndromes.