Background: Pain is a dynamic phenomenon resulting from the activity of both excitatory (e.g. sensitization) and inhibitory endogenous modulation systems. Preliminary experimental studies have shown diminished pain sensitivity in schizophrenia patients. The objective of the study was to investigate the role of excitatory and inhibitory systems on pain perception in schizophrenia.
Methods: Participants were 23 patients with a schizophrenia-spectrum disorder (DSM-IV criteria) and 29 healthy volunteers, who did not differ in age, sex or ethnicity. Excitatory and inhibitory systems were elicited using a temporal summation test (Peltier thermode) administered before and after activation of the diffuse noxious inhibitory control (DNIC) by means of a cold-pressor test.
Results: Time was a significant predictor of pain scores in controls, but not in patients. That is, pain ratings increased during the tonic thermal stimulation among controls but not in schizophrenia patients. When correlation coefficients (between time and pain ratings) for patients and controls were compared, the correlation coefficient emerged as significantly weaker in the schizophrenia group (Z=12.04; p=0.0001), suggesting a lack of sensitization in schizophrenia. DNIC was similar in magnitude in both patients and controls.
Conclusions: Diminished pain sensitivity in schizophrenia may be related to abnormal excitatory mechanisms, but not to DNIC. More studies are needed to better characterize the neurophysiological and neurochemical mechanisms involved in the lack of sensitization in schizophrenia.