Relationships between Irritable Bowel Syndrome Pain, Skin Temperature Indices of Autonomic Dysregulation, and Sensitivity to Thermal Cutaneous Stimulation

Abstract

This study evaluated relationships between irritable bowel syndrome (IBS) pain, sympathetic dysregulation, and thermal pain sensitivity. Eight female patients with diarrhea-predominant IBS and ten healthy female controls were tested for sensitivity to thermal stimulation of the left palm. A new method of response-dependent thermal stimulation was used to maintain pain intensity at a predetermined level (35%) by adjusting thermal stimulus intensity as a function of pain ratings. Clinical pain levels were assessed prior to each testing session. Skin temperatures were recorded before and after pain sensitivity testing. The temperature of palmar skin dropped (1.5°C) when the corresponding location on the opposite hand of control subjects was subjected to prolonged thermal stimulation, but this response was absent for IBS pain patients. The patients also required significantly lower stimulus temperatures than controls to maintain a 35% pain rating. Baseline skin temperatures of patients were significantly correlated with thermode temperatures required to maintain 35% pain ratings. IBS pain intensity was not significantly correlated with skin temperature or pain sensitivity. The method of response-dependent stimulation revealed thermal hyperalgesia and increased sympathetic tone for chronic pain patients, relative to controls. Similarly, a significant correlation between resting skin temperatures and thermal pain sensitivity for IBS but not control subjects indicates that tonic sympathetic activation and a thermal hyperalgesia were generated by the chronic presence of visceral pain. However, lack of a significant relationship between sympathetic tone and ratings of IBS pain casts doubt on propositions that the magnitude of IBS pain is determined by psychological stress.

Figure 1

The stimulus duration alternated between 1.0 second (series 1 and 3) and 0.8 seconds (series 2 and 4). Within each series, the temperature was modulated in a pain rating-dependent manner to maintain average pain intensity near a predetermined setpoint (35%). The change in temperature needed to compensate for the change in stimulus duration or ISI served as response variable. Stimulus durations are indicated above each bar, and interstimulus intervals remained constant at 3.0 seconds.

Figure 2

Non-tested palm. Average temperatures (ordinate) for the left and right palmar surfaces of control subjects and IBS patients at 3 time points (abscissa). Compared to the resting level (time 1), 5 minutes of pain testing for control subjects significantly reduced skin temperature (time 2), with some recovery by 3 minutes (time 3). Resting skin temperatures did not differ significantly for IBS and controls subjects. A significant decrease in skin temperature was not produced by pain testing of IBS patients.

Figure 3

Mean thermode temperature by series. Thermode temperatures (ordinate) averaged across 3 sessions of response-dependent stimulation that maintained an average eVAS rating of 35 for pain intensity. Thermode temperatures are shown for 4 sequential series of 25 stimuli with durations of 1.0 second (series 1 and 3) and 0.8 seconds (series 2 and 4). Hyperalgesia for cutaneous thermal stimulation was revealed by lower thermode temperatures within each series.