Pain sensitivity and endorphins in functional psychoses

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

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.

Race and histories of mood disorders modulate experimental pain tolerance in women

Thirty-two African American and 23 non-Hispanic white women were compared for experimental pain threshold and tolerance to thermal, ischemic, and cold pressor pain. Approximately half of each group had prior mood disorders (17 African Americans, 13 non-Hispanic whites), though all were free of current mood disturbance. Women with prior mood disorders were less sensitive to ischemic pain than women with no prior mood disorders (P < .05), whereas African Americans were more sensitive to ischemic pain than non-Hispanic whites, though only at pain tolerance (P < .001). For cold pressor pain, the effects of race were only seen in women with prior mood disorders, since African Americans with prior mood disorders were more sensitive than non-Hispanic whites with prior mood disorders (P < .05). These results indicate that experimental pain sensitivity in women is influenced by both race and histories of mood disorders.

PERSPECTIVE

We examined the association of race and histories of mood disorders with experimental pain sensitivity in an exclusively female sample. Our findings for racial differences in pain sensitivity may have implications for greater clinical pain in African American women. Persistent disturbance in pain modulatory mechanisms in women with a history of mood disorders may also have implications for the development of subsequent mood disturbances.

Food intake and reward mechanisms in patients with schizophrenia: implications for metabolic disturbances and treatment with second-generation antipsychotic agents

Obesity is highly prevalent among patients with schizophrenia and is associated with detrimental health consequences. Although excessive consumption of fast food and pharmacotherapy with such second-generation antipsychotic agents (SGAs) as clozapine and olanzapine has been implicated in the schizophrenia/obesity comorbidity, the pathophysiology of this link remains unclear. Here, we propose a mechanism based on brain reward function, a relevant etiologic factor in both schizophrenia and overeating. A comprehensive literature search on neurobiology of schizophrenia and of eating behavior was performed. The collected articles were critically reviewed and relevant data were extracted and summarized within four key areas: (1) energy homeostasis, (2) food reward and hedonics, (3) reward function in schizophrenia, and (4) metabolic effects of the SGAs. A mesolimbic hyperdopaminergic state may render motivational/incentive reward system insensitive to low salience/palatability food. This, together with poor cognitive control from hypofunctional prefrontal cortex and enhanced hedonic impact of food, owing to exaggerated opioidergic drive (clinically manifested as pain insensitivity), may underlie unhealthy eating habits in patients with schizophrenia. Treatment with SGAs purportedly improves dopamine-mediated reward aspects, but at the cost of increased appetite and worsened or at least not improved opiodergic capacity. These effects can further deteriorate eating patterns. Pathophysiological and therapeutic implications of these insights need further validation via prospective clinical trials and neuroimaging studies.

The relationship of somatization and depression to experimental pain response in women with temporomandibular disorders

OBJECTIVE

Patients with temporomandibular pain disorders (TMD) have greater experimental pain perception when compared with pain-free controls. Common psychological features of TMD include somatization and depression. The impact of depression on experimental pain perception has received considerable attention. However, the role of somatization on experimental pain in a chronic pain population has not been explored.

METHODS

Fifty-six women with TMD and 59 pain-free controls underwent three experimental pain procedures, including palpation at fixed amounts of pressure, pressure pain thresholds, and an ischemic pain task. Levels of depression and somatization were assessed using the Research Diagnostic Criteria for TMD. Multiple regression analyses were performed to determine the extent to which depression and somatization were associated with experimental pain response.

RESULTS

After controlling for characteristic pain intensity and depression, somatization explained a significant proportion of variance in numbers of masticatory sites rated as painful (R2 change = 6.7%, p = .046) with the full model explaining 16.4% of the variance (p = .024). This did not meet an adjusted level of statistical significance (p = .008). After controlling for characteristic pain, only depression added significantly to the model predicting ischemic pain threshold and tolerance. The full models including characteristic pain and depression explained 49% and 20% of the variance in ischemic pain threshold and tolerance, respectively.

CONCLUSIONS

These findings suggest that depression and somatization are associated with different measures of experimental pain. Somatization may be related to more attentional and perceptual measures of clinically relevant pain while depression may be related to more behavioral measures of pain.

Impact of depression on experimental pain perception: a systematic review of the literature with meta-analysis

OBJECTIVE

This systematic review and meta-analysis was performed to examine the impact of depression on the perception of experimental pain stimuli.

METHODS

CD-ROM databases and bibliographies were searched to identify studies comparing the psychophysical responses to experimental pain stimuli of depressed subjects with that of healthy controls. Effect sizes (Cohen's d) and probabilities were combined across studies; positive effect sizes indicated higher thresholds in depressed groups.

RESULTS

Six methodologically rigorous, independent studies were found comparing psychophysical responses to experimental pain stimuli in depressed subjects and healthy controls. Pain perception threshold was higher in depressed subjects (6 studies, d = 0.38, p =.001). This finding was not the result of publication bias. Absolute sensory perception threshold was much higher in depressed subjects (2 studies, d = 0.68, p =.002), though the findings for pain tolerance (2 studies) were too heterogeneous to enable us to combine results.

CONCLUSIONS

Depressed subjects are less likely to perceive a sensory stimulus as being painful compared with nondepressed controls. The influence of depression on attention to the pain stimulus may account for this effect. More studies are required to enable us to determine the impact of depression on absolute sensory perception threshold and pain tolerance. Furthermore, more studies would enable the examination of depression on the perception of different modalities.

Reduced tolerance and cardiovascular response to ischemic pain in minor depression

BACKGROUND

A paradoxical association between a higher prevalence of clinical pain and a reduced sensitivity to brief experimental pain seems to exist during depression.

METHODS

We assessed the responses to sustained ischemic pain produced by a maximal effort tourniquet procedure in 32 controls and 11 individuals with minor depression (Zung autoscale > or =50). Stethoscopic blood pressures and heart rates were monitored throughout the procedure.

RESULTS

Measures of pain threshold, and measures of pain intensity and pain unpleasantness during the ischemic procedure were similar in depressed and control subjects. Yet, the overall numerical ratings of ischemic pain during the procedure was 28% higher and pain tolerance was 44% lower in depressed compared to control subjects. Clinical pain complaints were reported by 91% of depressed but only by 41% of control subjects (P = 0.01). Sustained ischemic pain induced significant elevations of systolic and mean arterial blood pressures in controls but not in depressed subjects.

LIMITATIONS

The main limitation of the present study was the preponderance of females in the depressed group. Yet, we did not find significant gender differences in the sensory-affective and autonomic responses to ischemic pain in our sample.

CONCLUSIONS

These findings suggest alterations in the sensory and autonomic nervous systems during minor depression.

Pain perception in psychiatric disorders: a review of the literature

Aberrations of pain experience occur frequently in psychiatric disorders and hence pathological alterations in the basic mechanisms underlying pain experience can be expected. Nevertheless, pain perception, as one of the most important basic mechanisms of pain experience, has rarely been assessed experimentally in psychiatric disorders. The authors review the relevant experimental studies on pain perception in patients with anxiety disorders, schizophrenia, depression, eating disorders and personality disorders and suggest lines for future research. Finally, they point out that the experimental study of pain perception is useful not only in understanding aberrant pain experiences in psychiatric disorders but also in elucidating pathophysiological mechanisms because pain perception is controlled by neurochemical and neurohormonal functions known to be affected by psychiatric disease processes.

Pain insensitivity in schizophrenia. Case report and review of the literature

We describe a schizophrenic man whose lack of pain and related objective signs of a perforated small bowel led to a delay in diagnosis and surgical intervention. A review of the literature suggests that both psychodynamic and specific biologic factors can produce atypical presentations in psychotic patients with illnesses in which pain is characteristically a prominent presenting symptom. While research into the cause of altered pain perception in psychotic patients is continuing, clinicians should maintain a high index of suspicion of serious medical illness when evaluating such patients.

Anxiety and pain response changes across treatment: sensory decision analysis

Relationships between anxiety and pain perception were investigated by comparing pre- and post-pain reactions of highly anxious detoxified substance abusers categorized on the basis of anxiety level changes over treatment. Sensory decision theory methodology was applied to measure discriminative and decisional aspects of pain response. Men exhibiting significant pre-post-anxiety state decreases showed greater discriminability index increases and greater response bias index decreases at post-test, compared to their counterparts exhibiting minimal changes in severe anxiety levels across treatment. Findings have relevance for understanding pain perception and interventions in clinical samples.