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Pain perception in schizophrenia: evidence of a specific pain response profile.

OBJECTIVE
Ever since the characterization of schizophrenia, clinicians have noted abnormal pain sensitivity in their patients. The published literature, however, is inconsistent concerning the nature of the change reported. The objective of this study was to characterize the pain response profile of schizophrenic patients by providing both acute and prolonged (i.e., rapidly repeating) painful stimuli to schizophrenic participants and control subjects.


PARTICIPANTS
Twelve schizophrenic subjects and eleven controls were included in the final analysis. Diagnosis was made according to Diagnostic and Statistical Manual of mental disorders-4th edition, text revision (DSM-IV-TR) criteria.


METHODS
Intermittent, transcutaneous stimulations of the left sural nerve were administered to all participants. Painful sural nerve stimulations provoked a nociceptive flexion reflex response which was measured using an electromyographic recording of the bicep femoris muscle. Pain ratings were obtained using a 0-10 verbal numerical scale. Among schizophrenic participants, the relationship between subjective pain, reflex amplitude, and clinical features was investigated. The Positive and Negative Syndrome Scale, Calgary Depression Scale for Schizophrenia, and Subjective Scale to Investigate Cognition in Schizophrenia were used to evaluate clinical features.


RESULTS
Compared with controls, schizophrenic subjects showed increased sensitivity to acute pain (i.e., lower pain thresholds; P = 0.019), but decreased subjective pain sensitization (P = 0.027). Group differences in subjective pain sensitization were not accompanied by group differences in nociceptive reflex activity (P = 0.260), suggesting supraspinal origins to the change in pain experienced by schizophrenic subjects. Moreover, positive symptoms correlated negatively with pain threshold values among schizophrenic participants (r = -0.696, P = 0.012), suggesting that distortions of thought and function relate to pain sensitivity in schizophrenic patients.


CONCLUSION
Results indicate that schizophrenic subjects present a specific experimental pain response profile, characterized by elevated sensitivity to acute pain but reduced sensitivity to prolonged pain.