Experimental pain hypersensitivity in schizophrenic patients

The Impact of Childhood Maltreatment on Central Pain Processing in Individuals With Psychosis

INTRODUCTION

Exposure to childhood maltreatment can contribute to multiple behavioral and clinical manifestations, including the development of psychotic illnesses and pain-related abnormalities. Aberrant pain perception in individuals with psychosis may be associated with the worsening psychiatric symptoms, including an increase in mood episodes and a higher risk for suicidality. Despite the multiple connections between psychosis, pain, and childhood maltreatment, the combined investigation of these three domains remains limited.

METHODS

In this study, patients with schizophrenia (SZ, n = 20) or bipolar I disorder (BD, n = 24) and healthy controls (HC, n = 24) underwent a comprehensive clinical evaluation followed by quantitative sensory testing (QST), where behavioral sensitivity to thermal stimuli was quantified. Central pain circuitry was probed using a combination of functional and structural magnetic resonance imaging. Neuroimaging analyses focused on thermal stimulation fMRI responses, resting-state connectivity, and gray matter morphological properties.

RESULTS

fMRI demonstrated diminished sensorimotor activation during an evoked pain state for both SZ and BD patients, where reduced activity in thalamic subdivisions (i.e., pulvinar nucleus) in BD patients negatively correlates with the severity of childhood maltreatment. Resting-state connectivity analyses revealed altered connectivity of various cortical regions with the postcentral gyri and thalamic nuclei, suggesting potential altered neural mechanisms underlying pain perception in patients with SZ and BD. Morphological analysis identified reduced gray matter thickness in the postcentral sulcus of BD patients, which correlated with the severity of childhood maltreatment.

CONCLUSION

These findings provide insight into the multidimensional nature of clinical presentations in SZ and BD and contribute to our understanding of the complex relationship between childhood maltreatment and central pain processing in patients with psychotic illnesses.

The body interior in anorexia nervosa: from interoception to conceptual representation of body interior

Background

Body image disorders are well documented in anorexia nervosa (AN); however, knowledge of interoceptive awareness (IA) in this population remains poor. This descriptive study investigated whether and how the representation of the interior of the body may have an impact on IA.

Methods

The representations and knowledge of the body interior were evaluated with a drawing task in 34 women with AN and 34 healthy controls (HCs). A lexicometric analysis was performed on the vocabulary used to describe the drawn body parts in a structured interview. It was assumed that the conceptual representation of the body interior could be affected by or influence IA. Thus, the relationship between IA, measured with the heartbeat task and the ischemia-induction test, and the drawings was explored. Other scales, such as those of body shape, awareness or satisfaction, were used to assess affective representations of the body.

Results

The drawing, lexicometric and IA results were similar in the two groups. No correlations were found among IA, body representation scores and representation level of body interior. Only the representation of bones by the AN group was significantly different.

Discussion

Increased visual attention to the skeleton or greater awareness of bone health could explain the stronger representation of bones in the AN group. The psychophysical therapy received by some AN participants (73%) did not seem to have influenced IA. Our results do not support a relationship between IA and the representation of the body interior.Clinical trial registration:https://clinicaltrials.gov/, identifier NCT03988218.

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.

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.

Differences in the Opioid Consumption of Terminally Ill Schizophrenic and Nonschizophrenic Cancer Patients: Analysis of Secondary National Population Data

CONTEXT

It is uncertain whether terminally ill schizophrenic cancer patients are hypoalgesic or have disparities in pain management.

OBJECTIVES

The objective of this study was to analyze the dosage of opioids used in terminally ill cancer patients with and without schizophrenia.

METHODS

This is a population-based retrospective cohort study based on data derived from the Taiwan National Health Insurance Research Database. Patients aged >20 years and newly diagnosed between 2000 and 2012 with at least one of the six most common cancers were included. After 1:4 matching, 1001 schizophrenic cancer patients comprised the schizophrenia cohort, while 4004 cancer patients without schizophrenia comprised the nonschizophrenia cohort. The percentage of opioid use, accumulated dose, and average daily dose near the end of life were analyzed for each cohort using multiple logistic and linear regression models.

RESULTS

The percentage of opioid use was lower in the schizophrenic cohort than the nonschizophrenic cohort during the last month before death (69.6% vs. 84.8%, odds ratio = 0.40, 95% CI = 0.34-0.48). The accumulated dose of opioid consumption was also lower in the schizophrenic cohort (2407 mg vs. 3694 mg, P value < 0.05).

CONCLUSION

Near the end of life, cancer patients with schizophrenia use less opioid than their nonschizophrenic counterparts. Cognitive impairment may be a cause in the disparity in end-of-life care for terminally ill schizophrenic cancer patients. Thus, we should formulate a more accurate pain scale system and pay attention to their need for pain treatment.

A modality-specific dysfunction of pain processing in schizophrenia

Clinical observations showed that schizophrenia (SCZ) patients reported little or no pain under various conditions that are commonly associated with intense painful sensations, leading to a higher risk of morbidity and mortality. However, this phenomenon has received little attention and its underlying neural mechanisms remain unclear. Here, we conducted two experiments combining psychophysics, electroencephalography (EEG), and functional magnetic resonance imaging (fMRI) techniques to investigate neural mechanisms of pain insensitivity in SCZ patients. Specifically, we adopted a stimulus-response paradigm with brief stimuli of different sensory modalities (i.e., nociceptive, non-nociceptive somatosensory, and auditory) to test whether pain insensitivity in SCZ patients is supra-modal or modality-specific, and used EEG and fMRI techniques to clarify its neural mechanisms. We observed that perceived intensities to nociceptive stimuli were significantly smaller in SCZ patients than healthy controls, whereas perceived intensities to non-nociceptive somatosensory and auditory stimuli were not significantly different. The behavioral results were confirmed by stimulus-evoked brain responses sampled by EEG and fMRI techniques, thus verifying the modality-specific nature of the modulation of nociceptive information processing in SCZ patients. Additionally, significant group differences were observed in the spectral power of alpha oscillations in prestimulus EEG and the seed-based functional connectivity in resting-state fMRI (seeds: the thalamus and periaqueductal gray that are key nodes in ascending and descending pain pathways respectively), suggesting a possible contribution of cortical-subcortical dysfunction to the phenomenon. Overall, our study provides insight into the neural mechanisms of pain insensitivity in SCZ and highlights a need for systematic assessments of their pain-related diseases.

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.

Pain Processing in Psychiatric Conditions: A Systematic Review

Pain is a universal, multidimensional experience with sensory, emotional, cognitive, and social components, which is fundamental to our environmental learning when functioning typically. Understanding pain processing in psychiatric conditions could provide unique insight into the underlying pathophysiology or psychiatric disease, especially given the psychobiological overlap with pain processing pathways. Studying pain in psychiatric conditions is likely to provide important insights, yet, there is a limited understanding beyond the work in depression and anxiety. This is a missed opportunity to describe psychiatric conditions in terms of neurobiological alterations. To examine the research into the pain experiences of these groups and the extent to which a-typicality is present, a systematic review was conducted. An electronic search strategy was developed and conducted in several databases. The current systematic review included 46 studies covering five Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5) disorders: autism, attention-deficit hyperactivity disorder (ADHD), schizophrenia, personality disorder, and eating disorders, confirming tentative evidence of altered pain and touch processing. Specifically, hyposensitivity is reported in schizophrenia, personality disorder and eating disorder, hypersensitivity in ADHD, and mixed results for autism. Review of the research highlights a degree of methodological inconsistency in the utilization of comprehensive protocols, the lack of which fails to allow us to understand whether a-typicality is systemic or modality specific.

Physical effort exertion and pain: Links with trait-based risk for psychopathology

People with serious mental illness (SMI) are at an increased risk for physical health complications, such as cardiovascular disease and obesity. Low levels of physical activity is a major contributor to these health complications. One factor associated with limited physical activity in the broader sedentary population is pain. While preliminary findings suggest an association between lack of physical activity and pain in SMI, conclusions are still unclear. Thus, the goal of this correlational study was to examine associations between trait-based risk for psychopathology (hypomanic personality, schizotypy, and anhedonic depression) and the experience of pain following a physical endurance/effort task. Healthy participants (N = 43; 18 females) completed self-report measures of trait-based risk for psychopathology. They also reported on the experience of pain before and after the Time To Exhaustion (TTE) test. Findings revealed that risk for psychosis and anhedonic depression were associated with increases in pain following the TTE test, accounting for other key variables, such as age and self-reported physical exercise. Risk for mania was unrelated to changes in pain. These results suggest that the experience of pain in relation to physical endurance/effort may contribute to diminished physical activity among people at risk for SMI.

Past Pain Experience and Experimentally induced Pain Perception

Many intercurrent factors may be involved in the modulation of the pain message and its expression, such as the previous experience of pain built along the life. In this study, we aimed to determine whether susceptibility to experimentally induced pain is differentially influenced by the individual previous painful experience in subjects with schizophrenia (SC) major depression (MD), and controls (C).

METHODS

The SC (30), MD (32) and C (30) groups participated in experimental pain tests (application of pressure and induction of ischemia) after a semi-structured interview to make an inventory of the previous painful experiences, and the evaluation of anxiety either with autonomic (heart rate, blood pressure) or psychological (Hospital Anxiety Depression scale HAD) measures, and catastrophism.

RESULTS

The reported pain intensities, severities, duration, of the previous pain events, and the number of previous painful events were equivalent in the three groups, except for the number of painful events experimented before the last six months which was lower in the MD group. Experimental pain sensitivity was influenced by the diagnosis, the HAD scores or the number and intensities of previous lived painful events.

CONCLUSION

The lack of a past experience of pain was comparable for the different groups, suggesting that psychiatric disorders do not affect the experience of pain associated with daily life or past events. For each subject, the reported previous experience of pain influences the present feeling of pain.

Is Schizophrenia a Disorder of Consciousness? Experimental and Phenomenological Support for Anomalous Unconscious Processing

Decades ago, several authors have proposed that disorders in automatic processing lead to intrusive symptoms or abnormal contents in the consciousness of people with schizophrenia. However, since then, studies have mainly highlighted difficulties in patients' conscious experiencing and processing but rarely explored how unconscious and conscious mechanisms may interact in producing this experience. We report three lines of research, focusing on the processing of spatial frequencies, unpleasant information, and time-event structure that suggest that impairments occur at both the unconscious and conscious level. We argue that focusing on unconscious, physiological and automatic processing of information in patients, while contrasting that processing with conscious processing, is a first required step before understanding how distortions or other impairments emerge at the conscious level. We then indicate that the phenomenological tradition of psychiatry supports a similar claim and provides a theoretical framework helping to understand the relationship between the impairments and clinical symptoms. We base our argument on the presence of disorders in the minimal self in patients with schizophrenia. The minimal self is tacit and non-verbal and refers to the sense of bodily presence. We argue this sense is shaped by unconscious processes, whose alteration may thus affect the feeling of being a unique individual. This justifies a focus on unconscious mechanisms and a distinction from those associated with consciousness.

Impact of reward on pain threshold and tolerance to experimental pain (Cold Pressor Task) in healthy subjects and patients with schizophrenia

Reduced pain sensitivity is considered as a potential endophenotype of schizophrenia. Patient's motivation in pain experimental studies was neither assessed nor controlled. This study aimed to assess the effect of reward on pain in patients with schizophrenia compared to controls. Rewarded subjects showed higher pain threshold and tolerance compared to unrewarded subjects. Pain tolerance was significantly lower in patients than in controls when they were not rewarded. Reward resulted in an increase of pain tolerance with a higher manner in patients. This study suggests that better control of motivational aspects could improve assessment of pain sensitivity in schizophrenia.

Investigation of Rare Single-Nucleotide PCDH15 Variants in Schizophrenia and Autism Spectrum Disorders

Both schizophrenia (SCZ) and autism spectrum disorders (ASD) are neuropsychiatric disorders with overlapping genetic etiology. Protocadherin 15 (PCDH15), which encodes a member of the cadherin super family that contributes to neural development and function, has been cited as a risk gene for neuropsychiatric disorders. Recently, rare variants of large effect have been paid attention to understand the etiopathology of these complex disorders. Thus, we evaluated the impacts of rare, single-nucleotide variants (SNVs) in PCDH15 on SCZ or ASD. First, we conducted coding exon-targeted resequencing of PCDH15 with next-generation sequencing technology in 562 Japanese patients (370 SCZ and 192 ASD) and detected 16 heterozygous SNVs. We then performed association analyses on 2,096 cases (1,714 SCZ and 382 ASD) and 1,917 controls with six novel variants of these 16 SNVs. Of these six variants, four (p.R219K, p.T281A, p.D642N, c.3010-1G>C) were ultra-rare variants (minor allele frequency < 0.0005) that may increase disease susceptibility. Finally, no statistically significant association between any of these rare, heterozygous PCDH15 point variants and SCZ or ASD was found. Our results suggest that a larger sample size of resequencing subjects is necessary to detect associations between rare PCDH15 variants and neuropsychiatric disorders.

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.

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.

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.