Increased sensitivity to supra-threshold painful stimuli in patients with multiple functional somatic symptoms (MFS)

Many patients in a variety of medical settings suffer from persistently painful bodily symptoms that are not explained by known pathophysiological mechanisms. In the most severe cases, these patients complain of multiple functional somatic symptoms (MFS). We tested the hypothesis of reduced pain threshold and pain tolerance levels in patients with MFS. Twenty-two patients with MFS and 27 age- and sex-matched healthy control subjects volunteered for this study. The subjects received innocuous and noxious thermal stimuli to the volar forearm by means of a Peltier contact heat probe. We assessed pain threshold and pain tolerance with an ascending staircase method. Anxiety levels and hemodynamic (blood pressure, pulse rate) and endocrine (cortisol and prolactin release) responses were measured before and after pain testing. We found no group differences for any of the physiological or self-rated subjective emotional responses to the pain stressor. Contrary to the hypothesis, the pain threshold was not lower in MFS; the data even showed a trend in the opposite direction. Pain tolerance scores were identical in the two groups but they correlated negatively with the number of functional somatic symptoms in MFS patients. Importantly, patients had a smaller temperature range between their pain threshold and pain tolerance scores, suggesting that they differentiate poorly within the noxious range. Minor increases in stimulus intensity of supra-threshold painful stimuli may lead to disproportionate increases in pain intensity in MFS patients, suggesting a defunct endogenous pain modulatory system.