Influence of catechol-O-methyltransferase Val158Met on fear of pain and placebo analgesia.

Higher levels of fear have been shown to partly explain individual differences in placebo analgesic responding. The catechol-O-methyltransferase (COMT) rs4680 Val158Met polymorphism has been associated with both increased placebo analgesia and increased fear-related behavior, in what appears to be inconsistent findings in the literature. The aim of the study was therefore to investigate placebo analgesia and fear-related processes with regard to the COMT genotype, to sort out whether the Met-allele is associated with increased placebo analgesia or increased fear of pain (FOP). A 3 Group (Emla, placebo and natural history) by 5 Test (2 pretest, 3 posttests) mixed design was used (N = 223). A contact heat-evoked stimulator was used to induce pain, and FOP was quantified with the Fear of Pain Questionnaire-III. Saliva was obtained for genotyping. As expected, we observed a significant interaction of test by group (P < 0.01), with lower pain report in the placebo group compared with the natural history group (P < 0.01). There was a main effect of the COMT genotype on fear of medical pain (P = 0.032), and Met-allele carriers reported significantly higher fear of medical pain compared with the Val-allele (P = 0.044). We observed no effect of the COMT genotype on mean pain-level report or placebo analgesia. Thus, we conclude that the Met-allele seems to be associated with the negative emotional process of fear, but not with placebo analgesia.