Central processing of noxious somatic stimuli in patients with irritable bowel syndrome compared with healthy controls.
OBJECTIVE
To compare a central analgesic mechanism known as diffuse noxious inhibitory controls (DNIC) using somatic test stimuli and somatic conditioning stimuli, (CS) in irritable bowel syndrome (IBS) patients and healthy controls.


METHODS
Participants were 48 premenopausal females (27 with IBS), mean age of 29 years. The phasic heat test stimulus (peak temperature, 50 degrees C) was applied to the left palm. The DNIC effect, which measured reductions in average pain ratings (APR) during counter irritation (submersion of the participant's right hand in painful 12 degrees C circulating water) compared with baseline, was compared between groups. In addition, a second, counterbalanced, CS protocol (right hand submerged in nonpainful 32 degrees C circulating water) was performed. Differences in APR between the 2 counterirritation protocols were compared between groups to control for nonspecific effects known to influence DNIC. Psychologic measures and cardiovascular reactivity were also assessed.


RESULTS
IBS patients demonstrated smaller DNIC than controls (P=0.011, repeated measures analysis of variance), and greater state-anxiety, depression, catastrophizing, and anger-out expression (P<0.05). Group differences in DNIC were enhanced after controlling for nonspecific effects occurring during the nonpainful CS, and for psychologic measures (P=0.001, repeated measures analysis of covariance). There were no group differences in age, cardiovascular reactivity, APR, or pain ratings for the 12 degrees C CS.


CONCLUSIONS
These data demonstrate deficient DNIC in IBS. This is the first study to adequately control for alternative explanations of pain reduction during counterirritation. Only by controlling for nonspecific effects can evidence of deficient DNIC be attributed to dysregulation in endogenous analgesic mechanisms.
Heymen
Steve
S
Department of Medicine, Division of Gastroenterology, UNC Center for Functional Gastroenterology and Motility Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7080, USA. steve_heymen@med.unc.edu
Maixner
William
W
Whitehead
William E
WE
Klatzkin
Rebecca R
RR
Mechlin
Beth
B
Light
Kathleen C
KC
D000328:Adult; D000704:Analysis of Variance; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology* / Q000523:psychology*; D043183:Irritable Bowel Syndrome / Q000503:physiopathology*; D017288:Pain Threshold / Q000502:physiology*; D010812:Physical Stimulation / Q000009:adverse effects; D011594:Psychometrics; D011795:Surveys and Questionnaires