Comparison of experimental and acute clinical pain responses in humans as pain phenotypes

This study evaluates the sensitivity of normal subjects (N = 617; 369 women, 248 men) to experimentally induced pain including thermal stimuli and the cold pressor test to delineate individual response patterns and pain phenotypes. A subset of subjects (n = 157; 99 women and 58 men) also underwent standardized oral surgery, and the responses to clinically induced acute inflammatory pain were evaluated. A wide range of pain responses was found in both the experimental and clinical situations. The latency for withdrawal in the cold pressor test exhibited a dichotomous distribution of short and long times. Women exhibited higher responses to cold (P < .001) and thermal stimuli (P < .05) than men. Ethnicity affected pain responses to thermal stimuli ranging from 43 degrees C to 47 degrees C (P < .05) and cold stimuli (P < .001). However, neither gender nor ethnicity affected pain responses to clinically induced acute inflammatory stimuli. Cross-modality comparisons of responses within experimental pain showed strong correlations (P < .01) but weaker relationships with clinical inflammatory pain. These data suggest that the background factors and characteristics of experimental pain responses differ from those of clinical pain; therefore, experimental pain ratings alone are not sufficient to predict responses to clinically induced acute pain.

The findings of the present study suggest that investigations of pain phenotypes should take into consideration the subjects' gender and ethnicity and the pain-inducing stimuli. The predictive value of experimental pain for clinically induced pain is weak and not reliable.