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

Distributions of recorded pain in mental health records: a natural language processing based study

OBJECTIVE

The objective of this study is to determine demographic and diagnostic distributions of physical pain recorded in clinical notes of a mental health electronic health records database by using natural language processing and examine the overlap in recorded physical pain between primary and secondary care.

DESIGN, SETTING AND PARTICIPANTS

The data were extracted from an anonymised version of the electronic health records of a large secondary mental healthcare provider serving a catchment of 1.3 million residents in south London. These included patients under active referral, aged 18+ at the index date of 1 July 2018 and having at least one clinical document (≥30 characters) between 1 July 2017 and 1 July 2019. This cohort was compared with linked primary care records from one of the four local government areas.

OUTCOME

The primary outcome of interest was the presence of recorded physical pain within the clinical notes of the patients, not including psychological or metaphorical pain.

RESULTS

A total of 27 211 patients were retrieved. Of these, 52% (14,202) had narrative text containing relevant mentions of physical pain. Older patients (OR 1.17, 95% CI 1.15 to 1.19), females (OR 1.42, 95% CI 1.35 to 1.49), Asians (OR 1.30, 95% CI 1.16 to 1.45) or black (OR 1.49, 95% CI 1.40 to 1.59) ethnicities, living in deprived neighbourhoods (OR 1.64, 95% CI 1.55 to 1.73) showed higher odds of recorded pain. Patients with severe mental illnesses were found to be less likely to report pain (OR 0.43, 95% CI 0.41 to 0.46, p<0.001). 17% of the cohort from secondary care also had records from primary care.

CONCLUSION

The findings of this study show sociodemographic and diagnostic differences in recorded pain. Specifically, lower documentation across certain groups indicates the need for better screening protocols and training on recognising varied pain presentations. Additionally, targeting improved detection of pain for minority and disadvantaged groups by care providers can promote health equity.

Are Essential Trace Elements Effective in Modulation of Mental Disorders? Update and Perspectives

The emergence of mental disorders is associated with several risk factors including genetic and environmental susceptibility. A group of nutrients serves an especially important role in a number of essential neurodevelopmental processes through brain areas promoting the high degree of brain metabolism during early life, although almost all nutrients are needed. These include macronutrients and micronutrients (e.g., iron, magnesium, zinc, copper, selenium). Numerous nutritional psychiatry trials have been performed to examine the correlation of many individual nutrients with mental health, such as essential trace elements. The increased accumulation or lack of such components will facilitate an alternative metabolic pathway that can lead to many diseases and conditions of neurodevelopment. Mental functions have biochemical bases, so the impairment of such neurochemical mechanisms due to lack of trace elements can have mental effects. In psychological conditions such as depression, anxiety, schizophrenia, and autism, scientific studies demonstrate the putative role of trace element deficiency. Therefore, given the critical roles played by essential trace elements in the neurodevelopment and mental health, the effect of these elements' intake on the modulation of psychological functioning is reviewed.

Altered physical pain processing in different psychiatric conditions

Several reports indicate either increased or decreased pain sensitivity associated with psychiatric disorders. Chronic pain is highly prevalent in many of these conditions. We reviewed the literature regarding experimental pain sensitivity in patients with major depression, bipolar disorder, posttraumatic stress disorder (PTSD), generalized anxiety disorder, panic disorder, obsessive-compulsive disorder and schizophrenia. Electronic searches were performed to identify studies comparing experimental pain in patients with these conditions and controls. Across 31 depression studies, reduced pain threshold was noted except for ischemic stimuli, where increased pain tolerance and elevated sensitivity to ischemic pain was observed. A more pervasive pattern of low pain sensitivity was found across 20 schizophrenia studies. The majority of PTSD studies (n = 20) showed no significant differences compared with controls. The limited number of bipolar disorder (n = 4) and anxiety (n = 9) studies precluded identification of clear trends. Wide data variability was observed. Awareness of psychiatric patients' pain perception abnormalities is needed for active screening and addressing physical comorbidities, in order to enhance quality of life, life expectancy and mental health.

Evaluation of acute and chronic nociception in subchronically administered MK-801-induced rat model of schizophrenia

Patients diagnosed with schizophrenia have been reported to exhibit atypically low pain sensitivity and to vary in their experience of chronic pain. To the best of our knowledge, there has yet to be an animal study that provides information concerning the relationship between models of schizophrenia and pain. In the present study, we investigated several distinct nociceptive behaviors in a translational rat model of schizophrenia (0. 5 mg/kg MK-801, twice a day for 7 days followed by a 7-day washout period). The presence of the expected cognitive deficit was confirmed with novel object recognition (NOR) paradigm prior to nociception testing. MK-801-treated rats with lack of novelty interest in NOR testing showed: hyposensitivity to thermal and mechanical stimuli; short-term hypoalgesia followed by augmented hyperalgesia in response to formalin-induced spontaneous nociception and increased thermal and mechanical hyperalgesia in the complete Freund's adjuvant (CFA) induced chronic pain model. In conclusion, MK-801 induced antinociception effects for thermal stimuli in rats that were consistent with the decreased pain sensitivity observed in schizophrenia patients. Additionally, the amplified biphasic response exhibited by the MK-801 group in the formalin-induced spontaneous nociception test affirms the suitability of the test as a model of acute to delayed pain transition.

Dissecting pain processing in adolescents with Non-Suicidal Self Injury: Could suicide risk lurk among the electrodes?

Background

Although non‐suicidal self‐injury (NSSI) disorder is highly prevalent in adolescents, its relationship with pain system function and suicidality is still controversial. The present study was designed to assess the function of the nociceptive afferent pathways and the endogenous pain modulation in adolescent patients with NSSI and to longitudinally register any suicide attempt, describe its frequency and find a possible association between suicide, neurophysiological measures and psychological measures.

Methods

We enrolled 30 adolescents suffering from NSSI and 20 age‐ and gender‐matched healthy controls. Patients underwent a comprehensive psychological evaluation. Each participant underwent thermal pain thresholds of the quantitative sensory testing, laser‐evoked potential recording to study the ascending nociceptive pathway and the conditioned pain modulation testing to test the endogenous pain modulation.

Results

We found that patients with NSSI had a reduced amplitude of the N2 component of laser‐evoked potentials and an abnormal conditioned pain modulation. The amplitude of the N2 was associated with suicidal risk.

Conclusions

The deficit of the endogenous pain modulation likely depends on a saturation due to continuous pain solicitation. The strong association of a reduced amplitude of the N2 component with suicide suggests that it may serve as a possible biomarker in self‐harming adolescents.

Significance

The present study identifies the N2 component of laser‐evoked potentials as a possible neurophysiological biomarker of suicidal risk in patients with non‐suicidal self‐injury, therefore, raising the possibility for a non‐invasive test to identify subjects at higher risk of suicide among self‐harming patients.

Pain Sensitivity in Schizophrenia Spectrum Disorders: A Narrative Review of Recent Work

Many patients with schizophrenia seem relatively immune to physical pain while others complain of constant pain. This may result from disturbances or alterations of the sensory threshold for pain in populations with psychosis, a possibility for which there is some preliminary evidence. The inconsistency in pain perception may, in part, be explained by the treatments patients receive, but treatment-naïve patients also exhibit differences in response to pain. This suggests that decreased pain sensitivity may represent a specific psychosis endophenotype. Thus far, few experimental studies have investigated sensory thresholds, pain modalities, or other factors contributing to the perception or expression of physical pain in psychosis. A digital search for information on this topic was conducted in PubMed and Google Scholar. The result is a non-systematic, narrative review focusing on recent clinical and experimental findings of pain sensitivity in patients with psychosis. Importantly, physical and mental pain are closely connected constructs that may be difficult to differentiate. Our hope is that the review provides some clarity to the field in the specific context of schizophrenia.

The Opioid Interactions of the Antipsychotic Medications Risperidone and Amisulpride in Mice and Their Potential Use in the Treatment of Other Non-Psychotic Medical Conditions

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. The opioid epidemic in the USA has highlighted the need for alternative treatments for pain. Following reports on the opioid interactions of various antipsychotic medications, we speculated that the involvement of the opioid system in some of the antipsychotics' mechanism of action may suggest their potential use in the treatment of pain. Risperidone is a neuroleptic with a potent dopamine D2 and serotonin 5-HT2 receptor-blocking activity as well as a high affinity for adrenergic and histamine H1 receptors. Amisulpride is a neuroleptic which selectively blocks dopamine D2 and D3 receptors. Both had a potent antinociceptive effect on ICR mice tested with a tail flick assay. That effect on both medications was antagonized by naloxone, indicating that at least some of the antinociceptive effects were mediated by an opioid mechanism of action. Further investigation found that β-Funaltrexamine hydrochloride (β-FNA), naloxonazine, and nor-Binaltorphimine dihydrochloride (nor-BNI) reversed the antinociceptive effect of both risperidone and amisulpride. Naltrindole at a dose that blocked [D-Pen2,D-Pen5]enkephalin (DPDPE, δ analgesia) blocked notably amisplride effect and only partially reversed that of risperidone. Risperidone induced an antinociceptive effect, implying involvement of μ and κ-opioid and δ-opioid mechanisms. Amisulpride-induced antinociception was mediated through selective involvement of all three opioid receptor subtypes. These findings emphasize the need for clinical trials to assess the possibility of extending the spectrum of medications available for the treatment of pain.

An Obsessive-Compulsive Symptom-Related Headache in a Patient with Schizophrenia

Obsessive-compulsive symptoms are prevalent, manifold, and sometimes insidious in patients with schizophrenia. In this case study, we reported an intractable headache that bears a close relationship with obsessive-compulsive symptoms in a schizophrenia patient. In a series of treatments, the headache was miraculously susceptible to haloperidol treatment.

Minireview on the Connections between the Neuropsychiatric and Dental Disorders: Current Perspectives and the Possible Relevance of Oxidative Stress and Other Factors

Although the connections between neuropsychiatric and dental disorders attracted the attention of some research groups for more than 50 years now, there is a general opinion in the literature that it remains a clearly understudied and underrated topic, with many unknowns and a multitude of challenges for the specialists working in both these areas of research. In this way, considering the previous experience of our groups in these individual matters which are combined here, we are summarizing in this minireport the current status of knowledge on the connections between neuropsychiatric and dental manifestations, as well as some general ideas on how oxidative stress, pain, music therapy or even irritable bowel syndrome-related manifestations could be relevant in this current context and summarize some current approaches in this matter.

Painful Life Events in Psychiatric Disorders: A Quantitative and Qualitative Analysis

We reported in a previous study the painful events experienced in the past in subjects with schizophrenia or major depression, in comparison to controls, and related them to the experimental pain sensitivity, anxiety, and the diagnosis. We present here the detailed analysis of these past painful events, with the aim of determining whether schizophrenic, depressive and control groups are qualitatively (type of painful events experienced, emotional or sensory components associated with pain) and quantitatively (duration, severity, and intensity) comparable concerning their past painful experiences. The questionnaire used relies on memory and feelings and will provide an indication about the way pain is experienced and memorized in daily life. The reported history of pain was not the same in the three groups. Depressed subjects differed from the others by the number of reported painful events. Painful events of everyday life, such as trauma without fracture and wounds, were the most highly reported painful events for all groups. Surprisingly, the daily pain events are associated to affective component of pain perception. Other kinds of event were differently reported between the groups. Experience of pain appears to be memorized and reported differently depending on the psychiatric disorder and type of event. The characteristics of each individual, their previous experience, contribute to the expression of psychiatric disorders, including in the field of pain. Past pain experience should be taken into account when attending someone for pain.

Epidemiology of pain and relation to psychiatric disorders

Chronic pain is a common pain condition. Some psychiatric disorders, such as anxiety and depression, are also common in the general population. Epidemiological studies found that some psychiatric disorders are more commonly found among persons with chronic pain (e.g., headache, back pain) than those without chronic pain. Why those psychiatric disorders co-occur with chronic pain, however, is not well understood. Further, studies demonstrated that some psychiatric disorders, such as depression, increase the risk of chronic pain as well as its persistence. It is also recognized that chronic pain has a negative impact on the persistence of psychiatric disorders. The observations from clinical studies suggest that chronic pain is not a common comorbidity among individuals with other psychiatric disorders, such as dementia and schizophrenia. It is not clear if this is a consequence of any specific biological mechanism, or methodology problems in the studies. This paper provides an overview on the distribution of chronic pain and psychiatric disorders, followed by a review of studies that have demonstrated the association between psychiatric disorders and chronic pain.

The oral health of long-term psychiatric inpatients in Singapore

This cross-sectional study aims to describe the dental caries experience, treatment needs, and experience of dry mouth of 191 long-term psychiatric inpatients in Singapore. Medical history, dental caries experience [represented by the Decayed Missing or Filled Teeth index (DMFT)], salivary flow, and treatment needs were recorded. Information on brushing, pain (when eating), and xerostomia was gathered. Bivariate analysis was used to examine the associations of DMFT, saliva flow, the presence of salivary gland hypofunction (SGH), and xerostomia. Simple linear regression was used to examine the association between SGH and DMFT. The sample comprised 143 men (74.9%) and 48 women (25.1%), aged 24 to 80 years old. 169 patients (88.5%) had schizophrenia. DMFT ranged from 0 to 32, with a mean of 21.6 (SD 9.7). Mean DMFT scores were significantly higher among males and older patients. 77 of 176 patients (43.8%) were found to have SGH. SGH was associated with a higher mean DMFT. Those taking classical antipsychotics and anticholinergics had significantly lower mean saliva flow and tended to have SGH. 107 of 165 patients (64.8%) were found to experience xerostomia. Long-term psychiatric inpatients in Singapore have poor oral health, unmet treatment needs, and suffer from dry mouth.

Glutamatergic Response to Heat Pain Stress in Schizophrenia

Regulation of stress response involves top-down mechanisms of the frontal-limbic glutamatergic system. As schizophrenia is associated with glutamatergic abnormalities, we hypothesized that schizophrenia patients may have abnormal glutamatergic reactivity within the dorsal anterior cingulate cortex (dACC), a key region involved in perception of and reaction to stress. To test this, we developed a somatic stress paradigm involving pseudorandom application of safe but painfully hot stimuli to the forearm of participants while they were undergoing serial proton magnetic resonance spectroscopy to measure changes in glutamate and glutamine levels in the dACC. This paradigm was tested in a sample of 21 healthy controls and 23 patients with schizophrenia. Across groups, glutamate levels significantly decreased following exposure to thermal pain, while ratio of glutamine to glutamate significantly increased. However, schizophrenia patients exhibited an initial increase in glutamate levels during challenge that was significantly different from controls, after controlling for heat pain tolerance. Furthermore, in patients, the acute glutamate response was positively correlated with childhood trauma (r = .41, P = .050) and inversely correlated with working memory (r = -.49, P = .023). These results provide preliminary evidence for abnormal glutamatergic response to stress in schizophrenia patients, which may point toward novel approaches to understanding how stress contributes to the illness.

What causes psychosis? An umbrella review of risk and protective factors

Psychosis is a heterogeneous psychiatric condition for which a multitude of risk and protective factors have been suggested. This umbrella review aimed to classify the strength of evidence for the associations between each factor and psychotic disorders whilst controlling for several biases. The Web of Knowledge database was searched to identify systematic reviews and meta-analyses of observational studies which examined associations between socio-demographic, parental, perinatal, later factors or antecedents and psychotic disorders, and which included a comparison group of healthy controls, published from 1965 to January 31, 2017. The literature search and data extraction followed PRISMA and MOOSE guidelines. The association between each factor and ICD or DSM diagnoses of non-organic psychotic disorders was graded into convincing, highly suggestive, suggestive, weak, or non-significant according to a standardized classification based on: number of psychotic cases, random-effects p value, largest study 95% confidence interval, heterogeneity between studies, 95% prediction interval, small study effect, and excess significance bias. In order to assess evidence for temporality of association, we also conducted sensitivity analyses restricted to data from prospective studies. Fifty-five meta-analyses or systematic reviews were included in the umbrella review, corresponding to 683 individual studies and 170 putative risk or protective factors for psychotic disorders. Only the ultra-high-risk state for psychosis (odds ratio, OR=9.32, 95% CI: 4.91-17.72) and Black-Caribbean ethnicity in England (OR=4.87, 95% CI: 3.96-6.00) showed convincing evidence of association. Six factors were highly suggestive (ethnic minority in low ethnic density area, second generation immigrants, trait anhedonia, premorbid IQ, minor physical anomalies, and olfactory identification ability), and nine were suggestive (urbanicity, ethnic minority in high ethnic density area, first generation immigrants, North-African immigrants in Europe, winter/spring season of birth in Northern hemisphere, childhood social withdrawal, childhood trauma, Toxoplasma gondii IgG, and non-right handedness). When only prospective studies were considered, the evidence was convincing for ultra-high-risk state and suggestive for urbanicity only. In summary, this umbrella review found several factors to be associated with psychotic disorders with different levels of evidence. These risk or protective factors represent a starting point for further etiopathological research and for the improvement of the prediction of psychosis.

The Insula and Taste Learning

The sense of taste is a key component of the sensory machinery, enabling the evaluation of both the safety as well as forming associations regarding the nutritional value of ingestible substances. Indicative of the salience of the modality, taste conditioning can be achieved in rodents upon a single pairing of a tastant with a chemical stimulus inducing malaise. This robust associative learning paradigm has been heavily linked with activity within the insular cortex (IC), among other regions, such as the amygdala and medial prefrontal cortex. A number of studies have demonstrated taste memory formation to be dependent on protein synthesis at the IC and to correlate with the induction of signaling cascades involved in synaptic plasticity. Taste learning has been shown to require the differential involvement of dopaminergic GABAergic, glutamatergic, muscarinic neurotransmission across an extended taste learning circuit. The subsequent activation of downstream protein kinases (ERK, CaMKII), transcription factors (CREB, Elk-1) and immediate early genes (c-fos, Arc), has been implicated in the regulation of the different phases of taste learning. This review discusses the relevant neurotransmission, molecular signaling pathways and genetic markers involved in novel and aversive taste learning, with a particular focus on the IC. Imaging and other studies in humans have implicated the IC in the pathophysiology of a number of cognitive disorders. We conclude that the IC participates in circuit-wide computations that modulate the interception and encoding of sensory information, as well as the formation of subjective internal representations that control the expression of motivated behaviors.

Prevalence, characteristics and management of headache experienced by people with schizophrenia and schizoaffective disorder: a cross sectional cohort study

OBJECTIVES

Headache is the most common type of pain reported by people with schizophrenia. This study aimed to establish prevalence, characteristics and management of these headaches.

METHODS

One hundred participants with schizophrenia/schizoaffective disorder completed a reliable and valid headache questionnaire. Two clinicians independently classified each headache as migraine, tension-type, cervicogenic or other.

RESULTS

The 12-month prevalence of headache (57%) was higher than the general population (46%) with no evidence of a relationship between psychiatric clinical characteristics and presence of headache. Prevalence of cervicogenic (5%) and migraine (18%) was comparable to the general population. Tension-type (16%) had a lower prevalence and 19% of participants experienced other headache. No one with migraine was prescribed migraine specific medication; no one with cervicogenic and tension-type received best-practice treatment.

CONCLUSIONS

Headache is a common complaint in people with schizophrenia/schizoaffective disorder with most fitting recognised diagnostic criteria for which effective interventions are available. No one in this sample was receiving best-practice care for their headache.

Increased spinal pain sensitization in major depressive disorder: A pilot study

Although patients suffering from major depressive disorder (MDD) often complain from painful symptoms, the relationship between experimental pain processes and depression has yet to be clearly characterized. Only recently have studies employing temporal summation (TS) paradigms offered preliminary insight into the co-occurrence of pain and depression. This study sets out to evaluate the contribution of spinal and supraspinal processes in pain sensitization in MDD using a TS paradigm. Thirteen volunteers with no psychiatric disorders (controls) and fourteen MDD subjects were included in the analysis. Low-(0.14Hz) and high-(1Hz) frequency intermittent stimulations of the sural nerve were used to induce TS. Spinal pain sensitization was quantified by measuring the change in the amplitude of the nociceptive-specific flexion reflex (NFR) response, and supraspinal pain sensitization was obtained by measuring change in subjective pain rating, from the low- to high-frequency stimulation condition. We found an increased sensitization in the NFR response (p<0.05) in MDD subjects in the high-frequency condition, which did not translate into an increase of their subjective responses. However, we found a positive association between spinal sensitization and painful somatic symptoms in MDD subjects. Together, these results suggest increased spinal pain sensitization in MDD, which might explain the high prevalence of painful somatic symptoms in these patients.

Pain-processing abnormalities in bipolar I disorder, bipolar II disorder, and schizophrenia: A novel trait marker for psychosis proneness and functional outcome?

OBJECTIVES

Overlapping neural system dysfunctions, mainly involving the secondary somatosensory cortex (S2), the anterior cingulate cortex (ACC) and the anterior insular cortex (AIC), seem to be related to both pain-perception abnormalities and psychotic symptoms in schizophrenia (SCZ) and bipolar disorder (BD). Laser-evoked potentials (LEPs) were used to investigate pain-perception and central pain-processing abnormalities in SCZ, bipolar I disorder (BD-I), and bipolar II disorder (BD-II), and to evaluate their relationship with history of psychosis, and social-cognitive and functional impairments.

METHODS

Twenty patients with SCZ, 17 patients with BD-I, and 21 patients with BD-II who were all under similar pharmacological treatment underwent clinical, functional, and neuro-psychological assessment. LEPs were analyzed in patients and 19 healthy subjects (HS). LEPs elicit responses reflecting the activity of the S2 (N1 wave) and the ACC/AIC cortices (N2/P2 complex). A four-group ANOVA was conducted between patients and HS to compare pain-perceptive thresholds (PThs), N1, and N2/P2-LEP components.

RESULTS

Compared to HS: (i) patients with SCZ showed pain-processing and pain-perception abnormalities, as revealed by significantly higher PTh (P<.01), and lower N1 (P<.01) and N2/P2 (P<.01) amplitudes, (ii) patients with BD-I showed only pain-processing abnormalities, as revealed by significantly lower N1 (P<.05) and N2 (P<.01) amplitudes; and patients with BD-II did not differ for any of the LEP variables investigated. N1 and N2 amplitudes negatively correlated to history of psychosis (P<.01), social-cognition (P<.05), and real-world functioning (P<.01) measures in the whole group of patients.

CONCLUSIONS

To the best of our knowledge, this is the first study comparing central pain processing in patients with SCZ, BD-I, and BD-II. Our results suggest that pain-processing abnormalities may represent a novel locus of interest for research investigating trait markers of the psychosis spectrum.

Subclinical psychosis and pain in an English national sample: The role of common mental disorders

BACKGROUND

Information on the association between subclinical psychosis and pain is scarce, and the role of common mental disorders (CMDs) in this association is largely unknown. The aim of the current study was to therefore assess this association in the general population using nationally representative data from England.

METHODS

Data for 7403 adults aged≥16years were used from the 2007 Adult Psychiatric Morbidity Survey. Five forms of psychotic symptoms were assessed by the Psychosis Screening Questionnaire, while pain was assessed in terms of the level of its interference with work activity in the past four weeks. The Clinical Interview Schedule Revised (CIS-R) was used to assess anxiety disorders, depressive episode, and mixed anxiety-depressive disorder (MADD). Participants with probable or definite psychosis were excluded. The association between psychotic symptoms and pain was assessed by ordinal and binary logistic regression analysis.

RESULTS

When adjusted for confounders other than CMDs, psychotic symptoms were significantly associated with pain [e.g., the OR (95%CI) for the severest form of pain (binary outcome) was 1.78 (1.11-2.85)]. However, this association was no longer significant when CMDs were controlled for in most analyses. Anxiety disorders and depressive episode explained 34.8%-47.1% of the association between psychotic symptoms and pain, while this percentage increased to 62.7%-78.0% when the sub-threshold condition of MADD was also taken into account.

CONCLUSIONS

When coexisting psychotic symptoms and pain are detected, assessing for anxiety and depression (even at sub-threshold levels) may be important for determining treatment options.

Markedly Reduced Thermal Pain Perception in a Schizoaffective Patient with Tardive Dyskinesia

Several case reports have described stories of schizophrenia patients reporting no discomfort in response to several medical conditions which normally elicit pain. Comparatively, experimental studies performed on pain perception in schizophrenia have not documented hypoalgesic responses that are as frank as those reported in these clinical cases. Here, we report the case of a female patient with schizoaffective disorder, who displayed markedly reduced pain perception during an experimental heat pain paradigm. Compared to a large group of healthy volunteers that we tested in 3 previous studies using the same psychophysical procedure, the experimental temperature required to induce moderate pain was radically increased in this patient (z-score = 3.6). The patient had mild psychiatric symptoms and had insight into her symptoms. She had drug-induced dyskinetic symptoms. This case report illustrates that it is possible to observe marked reductions in pain perception in schizophrenia patients tested in experimental settings but that the phenomenon is relatively rare. Regardless of the exact nature of pain indifference in schizophrenia, it can delay diagnosis and treatment of medical problems in these patients. Future studies in the field will need to pay attention to drug-induced extrapyramidal symptoms.

Genetic Evaluation of Schizophrenia Using the Illumina HumanExome Chip

INTRODUCTION

Schizophrenia is a genetically heterogeneous disorder that is associated with several common and rare genetic variants. As technology involved, cost advantages of chip based genotyping was combined with information about rare variants, resulting in the Infinium HumanExome Beadchip. Using this chip, a sample of 493 patients with schizophrenia or schizoaffective disorder and 484 healthy controls was genotyped.

RESULTS

From the initial 242901 SNVs, 88306 had at least one minor allele and passed quality control. No variant reached genomewide-significant results (p<10(-8)). The SNP with the lowest p-value was rs1230345 in WISP3 (p = 3.05*10(-6)), followed by rs9311525 in CACNA2D3 (p = 1.03*10(-5)) and rs1558557 (p = 3.85*10(-05)) on chromosome 7. At the gene level, 3 genes were of interest: WISP3, on chromosome 6q21, a signally protein from the extracellular matrix. A second candidate gene is CACNA2D3, a regulator of the intracerebral calcium pathway. A third gene is TNFSF10, associated with p53 mediated apoptosis.

Neurophysiological responses to unpleasant stimuli (acute electrical stimulations and emotional pictures) are increased in patients with schizophrenia

Patients with schizophrenia have often been described as insensitive to nociceptive signals, but objective evidence is sparse. We address this question by combining subjective behavioral and objective neurochemical and neurophysiological measures. The present study involved 21 stabilized and mildly symptomatic patients with schizophrenia and 21 control subjects. We applied electrical stimulations below the pain threshold and assessed sensations of pain and unpleasantness with rating scales, and Somatosensory Evoked Potentials (SEPs/EEG). We also measured attention, two neurochemical stress indices (ACTH/cortisol), and subjective VEPs/EEG responses to visual emotional stimuli. Our results revealed that, subjectively, patients’ evaluations do not differ from controls. However, the amplitude of EEG evoked potentials was greater in patients than controls as early as 50 ms after electrical stimulations and beyond one second after visual processing of emotional pictures. Such responses could not be linked to the stress induced by the stimulations, since stress hormone levels were stable. Nor was there a difference between patients and controls in respect of attention performance and tactile sensitivity. Taken together, all indices measured in patients in our study were either heightened or equivalent relative to healthy volunteers.

Experimental pain sensitivity in subjects with major depression: Many pain complaints without hypersensitivity

OBJECTIVE

Patients with major depression frequently complain of pain, but conflicting data exist concerning their changes in pain sensitivity. This study aimed at comparing the sensitivity to moderate controlled pain between subjects presenting a major depressive episode (isolated and recurrent depressive episodes or a bipolar disorder), controls, and subjects with schizophrenia from a previous study.

METHOD

Pain sensitivity was assessed obtaining the visual analog scale (VAS) rating for the application of a 160 kPa pre-fixed pressure (fpVAS), the pressure corresponding to a VAS score of 3, and the time required to achieve a VAS score of 3 during ischemia induction. The effects of depression intensity, alexithymia, current and past general pain, and of six weeks of antidepressant treatment on fpVAS were investigated.

RESULTS

The results did not differ significantly between the depressed groups and the controls, without any effect of depression intensity. Presence of long-lasting pain and current pain felt on the day of testing correlated with fpVAS. The subjects of the depressed group were less sensitive than subjects with schizophrenia. FpVAS was significantly lower before and after antidepressant treatment in the subjects presenting clinical improvement.

CONCLUSIONS

No difference in experimental pain sensitivity and expression between major depressive episode subjects and controls, in opposite to pain complaints, is to be detected. The changes in the sensation of pain routinely attributed to subjects presenting depression may result from changes in a differential processing of pain signals, not in relation with the depression intensity, or the kind of depressive disorder.

Pain is independently associated with reduced health related quality of life in people with psychosis

The objective was to investigate the relationship between pain and health related quality of life (HRQOL) in people with psychosis. The study utilised a cross-sectional design including individuals with established psychosis from five Mental Health Trusts across England. Participants were classified as having pain or not and HRQOL was determined with the EQ-5D-3L. Covariates considered include the Positive and Negative Syndrome Scale (PANSS), the Montgomery Asberg Depression Rating Scale (MADRS) and Global Assessment of Functioning (GAF). Hierarchical multiple linear regression analyses were conducted. The final sample included 438 individuals with psychosis (47.5 years, SD 10.1, 193 females (42.9%)). 160 participants reported pain (36.5%) and compared to the non-pain group (N=278) they had significantly higher depressive symptoms (MADRS 14.91 vs 8.68), total (51.8 vs 47.9) and general PANSS scores (26.8 vs. 23.5) and lower overall HRQOL (54.7 vs 68.3). The final regression analysis (n=387) demonstrated that lower levels of pain were a predictor of better HRQOL (β=.173) after adjusting for the PANSS, MADRS and GAF. Depressive symptoms were the largest predictor of HRQOL (β=-.486). Only 1-2% of the sample were in receipt of analgesic medication suggesting pain is greatly overlooked despite its wider deleterious impact on HRQOL.

Probing the Dynamic Updating of Value in Schizophrenia Using a Sensory-Specific Satiety Paradigm

It has been proposed that both positive and negative symptoms in schizophrenia (SZ) may derive, at least in part, from a disrupted ability to accurately and flexibly represent the value of stimuli and actions. To assess relationships between dimensions of psychopathology in SZ, and the tendency to devalue food stimuli, on which subjects were fed to satiety, we administered a sensory-specific satiety (SSS) paradigm to 42 SZ patients and 44 controls. In each of 2 sessions, subjects received 16 0.7-ml squirts of each of 2 rewarding foods and 32 squirts of a control solution, using syringes. In between the 2 sessions, each subject was instructed to drink one of the foods until he/she felt "full, but not uncomfortable." At 10 regular intervals, interspersed throughout the 2 sessions, subjects rated each liquid for pleasantness, using a Likert-type scale. Mann-Whitney U-tests revealed group differences in SSS effects. Within-group tests revealed that, while controls showed an effect of satiety that was sensory specific, patients showed an effect of satiety that was not, devaluing the sated and unsated foods similarly. In SZ patients, we observed correlations between the magnitude of SSS effects and measures of both positive and negative symptoms. We argue that the ability to flexibly and rapidly update representations of the value of stimuli and actions figures critically in the ability of patients with psychotic illness to process salient events and adaptively engage in goal-directed behavior.

Promoting physical health for people with schizophrenia by reducing disparities in medical and dental care

OBJECTIVE

Acquiring a diagnosis of schizophrenia reduces life expectancy for many reasons including poverty, difficulties in communication, side-effects of medication and access to care. This mortality gap is driven by natural deaths; cardiovascular disease is a major cause, but outcomes for people with severe mental illness are worse for many physical health conditions, including cancer, fractures and complications of surgery. We set out to examine the literature on disparities in medical and dental care experienced by people with schizophrenia and suggest possible approaches to improving health.

METHOD

This narrative review used a targeted literature search to identify the literature on physical health disparities in schizophrenia.

RESULTS

There is evidence of inequitable access to and/or uptake of physical and dental health care by those with schizophrenia.

CONCLUSION

The goal was to reduce the mortality gap through equity of access to all levels of health care, including acute care, long-term condition management, preventative medicine and health promotion. We suggest solutions to promote health, wellbeing and longevity in this population, prioritising identification of and intervention for risk factors for premature morbidity and mortality. Shared approaches are vital, while joint education of clinicians will help break down the artificial mind-body divide.

Severe Burns and Amputation of Both Arms in the First Psychotic Episode of a Schizophrenic Patient

An alleged reduction of sensitivity to pain in people with schizophrenia has been reported, but the nature of this complex phenomenon has not been elucidated yet. Reports of insensitivity to burns from people with schizophrenia are extremely rare. We report the case of a 24-year-old man who set both of his arms on fire during the first break of paranoid schizophrenia. As a result of severe tissue damage, both of his limbs had to be amputated. Today, at the age of 59, the patient is physically and mentally rehabilitated and is adherent to treatment. Additionally, given the uncertainty about the true nature of the alleged hypoalgesia in schizophrenia, we postulate the need for a comprehensive phenomenological approach in the study of embodiment in people with this condition.

How much do we know about schizophrenia and how well do we know it? Evidence from the Schizophrenia Library

BACKGROUND

True findings about schizophrenia remain elusive; many findings are not replicated and conflicting results are common. Well-conducted systematic reviews have the ability to make robust, generalizable conclusions, with good meta-analyses potentially providing the closest estimate of the true effect size. In this paper, we undertake a systematic approach to synthesising the available evidence from well-conducted systematic reviews on schizophrenia.

METHOD

Reviews were identified by searching Medline, EMBASE, CINAHL, Current Contents and PsycINFO. The decision to include or exclude reviews, data extraction and quality assessments were conducted in duplicate. Evidence was graded as high quality if reviews contained large samples and robust results; and as moderate quality if reviews contained imprecision, inconsistency, smaller samples or study designs that may be prone to bias.

RESULTS

High- and moderate-quality evidence shows that numerous psychosocial and biomedical treatments are effective. Patients have relatively poor cognitive functioning, and subtle, but diverse, structural brain alterations, altered electrophysiological functioning and sleep patterns, minor physical anomalies, neurological soft signs, and sensory alterations. There are markers of infection, inflammation or altered immunological parameters; and there is increased mortality from a range of causes. Risk for schizophrenia is increased with cannabis use, pregnancy and birth complications, prenatal exposure to Toxoplasma gondii, childhood central nervous system viral infections, childhood adversities, urbanicity and immigration (first and second generation), particularly in certain ethnic groups. Developmental motor delays and lower intelligence quotient in childhood and adolescence are apparent.

CONCLUSIONS

We conclude that while our knowledge of schizophrenia is very substantial, our understanding of it remains limited.

The prevalence and moderators of clinical pain in people with schizophrenia: a systematic review and large scale meta-analysis

BACKGROUND

People with schizophrenia frequently have physical comorbidities that can cause pain. Experimental studies report reduced pain sensitivity among schizophrenia patients, but it remains unclear if clinically relevant pain is less prevalent in schizophrenia.

METHOD

We systematically searched major electronic databases from inception till 03/2014. Articles were included that reported the prevalence of clinical pain in people with schizophrenia. Two independent authors conducted searches, completed methodological quality assessment and extracted data. A random effects relative risks (RR) meta-analysis was conducted to determine the prevalence of all-cause and specific pain in schizophrenia, and the relative prevalence compared to the general population, and to assess moderators.

RESULTS

Altogether, 14 studies were included encompassing 242,703 individuals with schizophrenia (30.2-55.8 years) and 4,259,221 controls. Different types of pain were considered. The overall pooled prevalence of clinical pain in people with schizophrenia was 34.7% (95% CI=23.6-46.6). In the comparative analysis involving 7 studies with controls, the RR was 0.99 (95% CI=0.83-1.19). The pooled prevalence of headache among 94,043 individuals with schizophrenia was 29.9% (95% CI=3-69%) and the RR compared to 4,248,284 controls was 1.32 (95% CI=0.85-2.07). In moderator analyses, neither age, sex, study quality or pain assessment method influenced pain prevalence.

CONCLUSION

Clinical pain affects a third of people with schizophrenia and levels are similar with age- and sex-comparable controls. Future research is needed to determine if similar clinical pain prevalences in schizophrenia occur despite having more painful conditions, resulting from under-reporting, higher pain thresholds or lower help seeking behaviours.

Temporomandibular disorders in patients with schizophrenia using antipsychotic agents: a discussion paper

Patients with psychiatric problems show a tendency to develop temporomandibular disorders (TMD). Particularly, patients with schizophrenia are quite likely to have signs and symptoms of TMD due to the impairment of their oral health, the use of antipsychotic drugs, and other general health problems. In nonschizophrenic populations, TMD have been considered as the main cause of nondental pain in the orofacial region, involving mechanisms associated with changes in masticatory activity at the cortical and neuromuscular levels. Individuals with schizophrenia do not usually complain of pain, and TMD is misdiagnosed in this population. In this paper, we aimed to review the clinical aspects of TMD in people with schizophrenia on antipsychotic drug therapy.

Psychopathology of the bodily self and the brain: the case of schizophrenia

In the present paper, we review the recent empirical evidence on the neurobiological basis of a minimal notion of the self, the bodily self. We show the relationship between the body, its motor potentialities and the notion of minimal self. We argue that this approach can shed new light onto self-disturbances and social deficits characterizing schizophrenia. We discuss our approach with other views on the neural correlates of self-disturbances in schizophrenia and propose that cognitive neuroscience can today address the classical topics of psychopathology by adding a new level of description, finally enabling the correlation between the first-person experiential aspects of psychiatric diseases and their neurobiological roots.

Schizophrenia as a self-disorder due to perceptual incoherence

The aim of this review is to describe the potential relationship between multisensory disintegration and self-disorders in schizophrenia spectrum disorders. Sensory processing impairments affecting multisensory integration have been demonstrated in schizophrenia. From a developmental perspective multisensory integration is considered to be crucial for normal self-experience. An impairment of multisensory integration is called 'perceptual incoherence'. We theorize that perceptual incoherence may evoke incoherent self-experiences including depersonalization, ambivalence, diminished sense of agency, and 'loosening of associations' between thoughts, feelings and actions that lie within the framework of 'self-disorders' as described by Sass and Parnas (2003). We postulate that subconscious attempts to restore perceptual coherence may induce hallucinations and delusions. Increased insight into mechanisms underlying 'self-disorders' may enhance our understanding of schizophrenia, improve recognition of early psychosis, and extend the range of therapeutic possibilities.

Increased mortality in schizophrenia due to cardiovascular disease - a non-systematic review of epidemiology, possible causes, and interventions

BACKGROUND

Schizophrenia is among the major causes of disability worldwide and the mortality from cardiovascular disease (CVD) is significantly elevated. There is a growing concern that this health challenge is not fully understood and efficiently addressed.

METHODS

Non-systematic review using searches in PubMed on relevant topics as well as selection of references based on the authors' experience from clinical work and research in the field.

RESULTS

In most countries, the standardized mortality rate in schizophrenia is about 2.5, leading to a reduction in life expectancy between 15 and 20 years. A major contributor of the increased mortality is due to CVD, with CVD mortality ranging from 40 to 50% in most studies. Important causal factors are related to lifestyle, including poor diet, lack of physical activity, smoking, and substance abuse. Recent findings suggest that there are overlapping pathophysiology and genetics between schizophrenia and CVD-risk factors, further increasing the liability to CVD in schizophrenia. Many pharmacological agents used for treating psychotic disorders have side effects augmenting CVD risk. Although several CVD-risk factors can be effectively prevented and treated, the provision of somatic health services to people with schizophrenia seems inadequate. Further, there is a sparseness of studies investigating the effects of lifestyle interventions in schizophrenia, and there is little knowledge about effective programs targeting physical health in this population.

DISCUSSION

The risk for CVD and CVD-related deaths in people with schizophrenia is increased, but the underlying mechanisms are not fully known. Coordinated interventions in different health care settings could probably reduce the risk. There is an urgent need to develop and implement effective programs to increase life expectancy in schizophrenia, and we argue that mental health workers should be more involved in this important task.

Clinical pain in schizophrenia: a systematic review

Studies about clinical pain in schizophrenia are rare. Conclusions on pain sensitivity in people with schizophrenia are primarily based on experimental pain studies. This review attempts to assess clinical pain, that is, everyday pain without experimental manipulation, in people with schizophrenia. PubMed, PsycINFO, Embase.com, and Cochrane were searched with terms related to schizophrenia and pain. Methodological quality was assessed with the Mixed Methods Appraisal Tool. Fourteen studies were included. Persons with schizophrenia appear to have a diminished prevalence of pain, as well as a lower intensity of pain when compared to persons with other psychiatric diseases. When compared to healthy controls, both prevalence and intensity of pain appear to be diminished for persons with schizophrenia. However, it was found that this effect only applies to pain with an apparent medical cause, such as headache after lumbar puncture. For less severe situations, prevalence and intensity of pain appears to be comparable between people with schizophrenia and controls. Possible underlying mechanisms are discussed. Knowledge about pain in schizophrenia is important for adequate pain treatment in clinical practice.

PERSPECTIVE

This review presents a valuable insight into clinical pain in people with schizophrenia.

Isolation rearing reduces mechanical allodynia in a mouse model of chronic inflammatory pain

Social isolation rearing in mice after weaning reduces pain sensitivity to acute pain, and this hypoalgesia is mediated by the descending serotonergic pain inhibitory system in which the spinal serotonin (5-HT)1A receptor is involved. However, it is not known whether isolation rearing affects pain sensitivity to neuropathic or inflammatory chronic pain. In this study, we examined the effects of isolation rearing on chronic pain induced by Freund's complete adjuvant (FCA) and partial sciatic nerve ligation using the von Frey test (to assess mechanical allodynia) and the plantar test (to assess thermal hyperalgesia). In the FCA model, isolation rearing reduced mechanical allodynia, but not thermal hyperalgesia. In contrast, isolation rearing had no effect on allodynia or hyperalgesia in the sciatic nerve ligation model. The isolation rearing-induced inhibition of allodynia was alleviated by intrathecal injection of WAY100635, a selective 5-HT1A receptor antagonist. FCA increased 5-HT turnover and decreased 5-HT1A receptor expression in the spinal cord of group-reared mice, while it did not have these effects in isolation-reared mice. These results suggest that FCA suppresses the serotonergic pain inhibitory system selectively in group-reared mice. Moreover, systemic administration of osemozotan, a selective 5-HT1A receptor agonist, inhibited FCA-induced mechanical allodynia in group-reared mice, and this effect of the drug was suppressed by intrathecal injection of WAY100635. Collectively, these findings suggest that isolation rearing selectively reduces FCA-induced mechanical allodynia in mice and that this effect is mediated by the activation of spinal 5-HT1A receptors.

Involvement of spinal 5-HT1A receptors in isolation rearing-induced hypoalgesia in mice

RATIONALE

Isolation rearing in rodents causes not only abnormal behaviors which resemble the clinical symptoms of schizophrenia but also hypoalgesia in thermal nociception models. However, the mechanism of the hypoalgesia is not known.

OBJECTIVES

The present study investigated the effect of isolation rearing on acute pain and the descending pain inhibitory pathways in mice.

RESULTS

Rearing in isolation for 6 weeks from post-weaning reduced pain sensitivity in the hot plate test and acetic acid-induced writhing test. Isolation rearing also reduced the intraplantar capsaicin-induced licking behavior. Capsaicin increased c-Fos expression, a neuronal activity marker, in the spinal cord and primary somatosensory cortex both in group- and isolation-reared mice, but this effect did not differ between groups. On the other hand, c-Fos expression in the anterior cingulate cortex, periaqueductal gray matter, and rostral ventromedial medulla, but not in the spinal cord or somatosensory cortex, was enhanced by isolation rearing. Systemic administration of WAY100635 (serotonin (5-HT)1A receptor antagonist), but not of ketanserin (5-HT2 receptor antagonist), prazosin (α1-adrenoceptor antagonist), or yohimbine (α2-adrenoceptor antagonist), attenuated isolation rearing-induced hypoalgesia in capsaicin-induced licking behavior. Attenuation of isolation rearing-induced hypoalgesia was also observed following the intrathecal injection of WAY100635. Naloxone, an opioid receptor antagonist, did not affect the hypoalgesia in isolation-reared mice.

CONCLUSIONS

These findings suggest that isolation rearing causes hypoalgesia in mouse models of acute pain and imply that the spinal 5-HT1A receptor activation probably through descending serotonergic inhibitory pathway is involved in isolation rearing-induced hypoalgesia.

Alteration of pain recognition in schizophrenia

BACKGROUND

Schizophrenia patients display impaired recognition of their own emotions and those of others and deficits in several domains of empathy. The first-person experience of pain and observing others in pain normally trigger strong emotional mechanisms. We therefore hypothesized that schizophrenia patients would display impaired recognition and categorization of both their own pain and the pain of others.

METHODS

We studied 29 patients (18 men/11 women; 36 ± 13 years old) with paranoid schizophrenia-spectrum disorder and 27 healthy volunteers (20 men/7 women; 31 ± 9 years old) matched for age, gender, IQ and socio-cultural level. We assessed symptom severity and theory of mind. The participants' ability to detect and categorize pain in others was assessed with the sensitivity to expressions of pain (STEP) test, which is based on facial expressions, and another dynamic test involving a series of video sequences showing various pain-inducing events. The ability of patients to evaluate their own pain was assessed with the situational pain questionnaire (SPQ), which includes a series of questions assessing how one would expect to feel in different imaginary situations. Empathic tendencies were assessed with the interpersonal reactivity index.

RESULTS

Patients and controls differed significantly in STEP, pain video and SPQ scores. By contrast with control subjects, the patients' pain judgements were not correlated with their affective or cognitive empathic capacities.

CONCLUSIONS

Schizophrenic patients have a deficit of the identification and categorization of pain both in themselves and in others.

Lack of insula reactivity to aversive stimuli in schizophrenia

Patients with schizophrenia may have altered pain perception, as suggested by clinical reports of pain insensitivity, and recent neuroimaging findings. Here, we examined neural responses to an aversive electrical stimulus and the immediate anticipation of such a stimulus using fMRI and a classical conditioning paradigm, which involved pairing an electrical shock with a neutral photograph. Fifteen men with schizophrenia and 13 healthy men, matched for demographic characteristics, electrical stimulation level and scan movement, were studied. The shock induced robust responses in midbrain, thalamus, cingulate gyrus, insula and somatosensory cortex in both groups. However, compared to controls, the schizophrenic patients displayed significantly lower activation of the middle insula (p(FWE)=0.002, T=5.72, cluster size=24 voxels). Moreover, the lack of insula reactivity in the schizophrenia group was predicted by the magnitude of positive symptoms (r=-0.46, p=0.04). In contrast, there were no significant differences between the two groups in the magnitude of neural responses during anticipation of the shock. These findings provide support for the existence of a basic deficit in interoceptive perception in schizophrenia, which could play a role in the generation and/or maintenance of psychotic states.

Comparative health care use patterns of people with schizophrenia near the end of life: a population-based study in Manitoba, Canada

CONTEXT

The rate of health care and palliative care utilization for patients with schizophrenia near the end-of-life is currently unknown.

OBJECTIVE

Compare rate of health care services, including palliative care, used in the last 6-24months of life for patients with and without schizophrenia.

DESIGN

Using the de-identified administrative data Repository at the Manitoba Centre for Health Policy; a matched cohort study between 1995/96 and 2007/08,comparing healthcare services utilized six months to two years prior to death of all (de-identified) decedents with a diagnosis of schizophrenia >10years to decedents without a schizophrenia diagnosis.

SETTING

province of Manitoba, Canada (population 1.235 million).

PARTICIPANTS

Schizophrenia definition: ICD-9-CM 295, or ICD-10-CA code of F20, F21, F23.2, F25 in hospital or physician files, over a 12-year period 1987-1998, in the 12years prior to death for each individual. Decedents were matched (1:3) on age, sex, geography and date of death ±2months.

MAIN OUTCOME MEASURES

Health service utilization rates within six-months to two years prior to death.

RESULTS

In the last six months of life, compared to their matched cohort: decedents with schizophrenia had higher rates (52.1% vs. 24.4%, p<.00001) and number of days (89.2 vs. 40.3days, p<.0001) residing in a nursing home; had higher ambulatory visit rates to general practitioners (6.4 vs. 5.5 visits per person, p<.0001), higher rate of visits to psychiatrists (0.53 vs. 0.07 visits per person) and lower rates of seeing other specialists. They were less likely to have opioid analgesia (aRR=0.7157, p-value=0.0006) or to receive palliative care (aOR=0.48, 95% CI 0.41-0.57).

CONCLUSION

End-of-life care is lacking for patients with schizophrenia. Compared to their matched cohort, these patients were much more likely to die in nursing homes, less likely to see specialists (other than psychiatrists), less likely to be prescribed analgesics, and less likely to receive palliative care.

Increased cold and heat pain thresholds influence the thermal grill illusion in schizophrenia

BACKGROUND

Patients with schizophrenia show decreased sensitivity towards clinical and experimental painful conditions. To date, the exact underlying mechanisms are not completely understood. One method to examine central integrative processes of pain perception is the thermal grill illusion (TGI), in which interlacing cold and warm bars create the illusion of a painful sensation.

METHODS

In 18 unmedicated patients with acute paranoid schizophrenia, cold and heat pain thresholds (CPT/HPT) as well as the perception of the TGI were examined and compared to 18 matched controls. In addition, symptom scales were obtained in order to relate pain perception to psychopathology.

RESULTS

CPT and HPT were significantly increased in patients compared to controls. In the range of TGI stimuli that were perceived painful by controls, patients did not indicate painful sensations, instead the stimulus response curve of TGI pain perception was shifted towards higher stimulus intensities, i.e., greater temperature differentials between cold and warm bars. This increase was comparable to that seen in CPT and HPT. There was no association with psychopathology for any pain parameter.

CONCLUSIONS

CPT and HPT, as well as temperature differentials for the perception of the TGI were increased in patients with schizophrenia as compared to controls. Similar to visual illusions, in which reduced contrast sensitivity has been shown to alter the perception of illusions, the discriminatory somatosensory deficit, which is reflected in higher CPT and HPT as well as the previously reported increased warmth perception thresholds, might account for the attenuation of TGI in patients.