Hypoalgesia in schizophrenia is independent of antipsychotic drugs: A systematic quantitative review of experimental studies

Abstract

Diminished sensitivity to pain in schizophrenia has been reported since the early works of Bleuler [Bleuler E. Textbook of psychiatry (trans. Brill HA, 1951). New York: Dover Publications; 1911] and Kraepelin [Kraepelin E. Dementia praecox and paraphrenia. Edinburgh, Scotland: E and S Livingstone; 1919]. Over the last decade, experimental studies have measured pain perception in schizophrenia and produced mixed results. This meta-analysis sought to determine if the scientific literature confirms the hypothesized hypoalgesia in schizophrenia. The search was performed with computerised literature databases. A study was retained in the meta-analysis if: (i) it comprised a group of schizophrenia patients, compared to a control group of healthy volunteers; and (ii) pain was measured via experimental procedures (e.g. thermal, electrical, or mechanical stimuli). Using Comprehensive Meta-Analysis-2, effect size estimates of the differences in pain scores (all pain scores derived from all pain tests) between schizophrenia patients and healthy volunteers were calculated. Eleven studies were included in the meta-analysis. For the composite analysis, a positive, moderate, and significant effect size estimate emerged (N=497; Hedges's g=0.437; p=0.005), suggesting that patients with schizophrenia show a diminished response to experimentally-induced pain. Secondary analyses showed that: (i) drug-free patients also have hypoalgesic responses; and that (ii) sensory thresholds are increased in schizophrenia patients. This meta-analysis substantiates the hypothesis of a diminished pain response in schizophrenia. The study also suggests that hypoalgesia in schizophrenia cannot be solely explained by the effects of antipsychotic drugs, and that it may not be a pain-specific blunted response. Further studies are warranted to determine the clinical and biological correlates, and the social and health consequences, of hypoalgesia in schizophrenia.

Decreased pain sensitivity among people with schizophrenia

“…Our results are consistent with a more preliminary prior meta-analysis [43]. In this paper, the authors had reported hypoalgesia to experimentally induced pain that was independent of antipsychotic treatment using a composite analysis in which any pain measure, albeit very divergent parameters were pooled together.…”

“…In line with a previous metaanalysis [43], we examined the funnel plot of the composite outcome searching for extreme outliers and removed from the database and all analyses one extreme publication bias outlier [39]. Across the resultant sample of 17 studies, we first conducted a composite analysis pooling aggregated pain measure data on pain threshold, pain tolerance and sensory threshold together from all studies to establish an overall difference in pain sensitivity.…”

“…Only one previous review [43], with a last search date of almost a decade ago, investigated differences in experimental pain responses in people with schizophrenia versus controls. The authors aggregated all different types of pain measures together in a composite analysis and found that people with schizophrenia appeared to exhibit hypoalgesia.…”

The evaluation of headache in patients with schizophrenia: a case-control study

“…The tendency of reduction in headache frequency in this group of patients might be explained by the less sensitivity to pain (8). Previous studies reported that the loss of pain sensation and the reduction of pain sensitivity were present (9)(10)(11). Although results of studies investigating the reduction of the pain sensation in schizophrenia are not convincing, four different kind of study types have provided data to support this argument; a) Clinical case reports that determine the reduced or no pain sensation in patients with schizophrenia during different kinds of painful medical situations (ruptured appendix, perforated bowel, peritonitis, etc.…”

“…Although results of studies investigating the reduction of the pain sensation in schizophrenia are not convincing, four different kind of study types have provided data to support this argument; a) Clinical case reports that determine the reduced or no pain sensation in patients with schizophrenia during different kinds of painful medical situations (ruptured appendix, perforated bowel, peritonitis, etc. ), b) Population-based studies that have shown the increased prevalence of reduction or loss of the pain sensation in schizophrenic patients who suffer from a painful medical condition, c) Population-based studies that defined the reduced prevalence of schizophrenia in patients who suffer from pain and d) Experimental studies have shown that the pain threshold is high in patients with schizophrenia (11).…”