A modality-specific dysfunction of pain processing in schizophrenia

Progress in the mechanisms of pain associated with neurodegenerative diseases

Neurodegenerative diseases (NDDs) represent a class of neurological disorders characterized by the progressive degeneration or loss of neurons, impacting millions of individuals globally. In addition to the typical manifestations, pain is a prevalent symptom associated with NDDs, seriously impacting the quality of life for patients. The pathogenesis of pain associated with NDDs is intricate and multifaceted. Currently, the clinical management of NDDs-related pain symptoms predominantly relies on conventional pharmacological agents or physical therapy. However, these approaches often fail to produce satisfactory outcomes. This article summarizes the underlying mechanisms of major NDDs-associated pain: Neuroinflammation, Brain and spinal cord dysfunctions, Mitochondrial dysfunction, Risk gene and pathological protein, as well as Receptor, channel, and neurotransmitter. While numerous studies have investigated the downstream pathological processes associated with these mechanisms, there remains a significant gap in identifying the key initiating factors. Specifically, there is insufficient evidence for the upstream elements that activate microglia and astrocytes in neuroinflammation leading to pain in NDDs. Likewise, there is an absence of upstream factors elucidating how dysfunctions in the brain and spinal cord, as well as mitochondrial impairments, contribute to the development of pain. Furthermore, the specific mechanisms through which hallmark pathological proteins related to NDDs contribute to these pathological processes remain inadequately understood. The objective of this article is to synthesize the existing mechanisms underlying pain associated with NDDs, including Alzheimer's disease, Parkinson's disease, Huntington's disease, Schizophrenia, Amyotrophic lateral sclerosis, and Multiple sclerosis, while also identifying gaps and deficiencies in these mechanisms. This paper offers insights for future research trajectories. Given the intricate pathogenesis of NDDs-related pain, it emphasizes that a promising short-term strategy is combination therapy-intervening concurrently in multiple pathological processes-akin to the cocktail approach utilized in treating acquired immunodeficiency syndrome (AIDS). For long-term advancements, achieving breakthroughs in the treatment of the NDDs themselves will remain essential for alleviating accompanying pain symptoms.

Prescription opioid dispensing patterns among patients with schizophrenia or bipolar disorder

BACKGROUND

Patients with schizophrenia (SZ) or bipolar disorder (BD) may have increased risk of complications from prescribed opioids, including opioid-induced respiratory depression. We compared prescription opioid pain medication dispensing for patients with SZ or BD versus controls over 5 years to assess dispensing trends.

METHODS

This retrospective, observational study analysed US claims data from the IBM® MarketScan® Commercial and Multi-State Medicaid databases for individuals aged 18-64 years with prevalent SZ or BD for years 2015-2019 compared with age- and sex-matched controls. Baseline characteristics, comorbidities, and medication use were assessed. Proportions of individuals dispensed prescription opioids chronically (ie, ≥70 days over a 90-day period or ≥ 6 prescriptions annually) or nonchronically (≥1 prescription, chronic definition not met) were assessed.

RESULTS

In 2019, the Commercial and Medicaid databases contained records for 4773 and 30,179 patients with SZ and 52,780 and 63,455 patients with BD, respectively. Patients with SZ or BD had a higher prevalence of comorbidities, including pain, versus controls in each analysis year. From 2015 to 2019, among commercially insured patients with SZ, chronic opioid-dispensing proportions decreased from 6.1% (controls: 2.7%) to 2.3% (controls: 1.2%) and, for patients with BD, from 11.4% (controls: 2.7%) to 6.4% (controls: 1.6%). Chronic opioid dispensing declined in Medicaid-covered patients with SZ from 15.0% (controls: 14.7%) to 6.7% (controls: 6.0%) and, for patients with BD, from 27.4% (controls: 12.0%) to 12.4% (controls: 4.7%). Among commercially insured patients with SZ, nonchronic opioid dispensing decreased from 15.5% (controls: 16.4%) to 10.7% (controls: 11.0%) and, for patients with BD, from 26.1% (controls: 17.5%) to 20.0% (controls: 12.2%). In Medicaid-covered patients with SZ, nonchronic opioid dispensing declined from 22.5% (controls: 24.4%) to 15.1% (controls: 12.7%) and, for patients with BD, from 32.3% (controls: 25.9%) to 24.6% (controls: 13.6%).

CONCLUSIONS

The proportions of individuals dispensed chronic or nonchronic opioid medications each year were similar between commercially and Medicaid-insured patients with SZ versus controls and were higher for patients with BD versus controls. From 2015 to 2019, the proportions of individuals who were dispensed prescription opioids chronically or nonchronically decreased for patients with SZ or BD and controls.

Pain-preferential thalamocortical neural dynamics across species

Searching for pain-preferential neural activity is essential for understanding and managing pain. Here, we investigated the preferential role of thalamocortical neural dynamics in encoding pain using human neuroimaging and rat electrophysiology across three studies. In study 1, we found that painful stimuli preferentially activated the medial-dorsal (MD) thalamic nucleus and its functional connectivity with the dorsal anterior cingulate cortex (dACC) and insula in two human functional magnetic resonance imaging (fMRI) datasets (n = 399 and n = 25). In study 2, human fMRI and electroencephalography fusion analyses (n = 220) revealed that pain-preferential MD responses were identified 89-295 ms after painful stimuli. In study 3, rat electrophysiology further showed that painful stimuli preferentially activated MD neurons and MD-ACC connectivity. These converging cross-species findings provided evidence for pain-preferential thalamocortical neural dynamics, which could guide future pain evaluation and management strategies.

Pain sensitivity in patients with schizophrenia: a systematic review and meta-analysis

BACKGROUND

Alterations in pain perception have been observed in people diagnosed with schizophrenia. Some research suggests the existence of a possible hyposensitivity, while others describe a hypersensitivity to pain in people with schizophrenia. In summary, the studies present contradictory results.

Self-monitoring in schizophrenia: Weighting exteroceptive visual signals against self-generated vestibular cues

Disturbances in self-monitoring are core symptoms of schizophrenia. Some research suggests an over-reliance on exteroceptive cues and a reduced weighting of self-generated interoceptive signals to guide perception. The vestibular sense provides important self-generated information about the body in space. Alterations of vestibular function are reported in schizophrenia, but it is unknown whether internally generated vestibular information is discounted in favour of exteroceptive input. In this study, we test for evidence of an over-reliance on exteroceptive visual cues and a reduced weighting of vestibular signals in guiding perception. In a group of individuals with schizophrenia and healthy controls, we used a well-studied visual illusion - the Tilt Illusion - to probe the respective weight given to visual and vestibular cues in judging line orientation. The Tilt Illusion reveals that perceived orientation of a vertical grating is biased by the orientation in its surround. This illusion increases when the head is tilted, due to the reduced reliability of vestibular information that would otherwise provide an internally generated reference for vertical. We predicted that an over-reliance on exteroceptive cues in schizophrenia would lead to a reduced susceptibility to the effects of head position on Tilt Illusion strength. We find no difference between patients and controls. Both groups show comparable Tilt Illusion magnitudes that increase when the head is tilted. Thus, our findings suggest that chronic patients with schizophrenia adequately combine self-generated vestibular cues and exteroceptive visual input to judge line verticality. A stronger reliance on exteroceptive information over internally generated signals in guiding perception is not evident in our data. Deficits in self-monitoring might therefore be modality specific or state dependant.

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.

The effects of long-term menstrual pain on pain empathy in women with primary dysmenorrhea

ABSTRACT

Primary dysmenorrhea (PDM) is not only a painful experience but also affects the psychological and affective states of women. Neuroimaging studies have revealed shared neural substrates for somatic and empathic pains in healthy subjects. However, little is known about the relationship between pain intensity and pain empathy in pain disorders. The cyclic nature of PDM makes it a unique model for investigating this issue during a patients' pain phase. To study how long-term pain modulates empathy for pain, T1-weighted magnetic resonance imaging scans were obtained in 39 PDM patients and 41 matched female healthy controls during menstruation. Subjects viewed static visual stimuli of the limbs submitted to painful and nonpainful stimulation to solicit empathy. The visual analogue scale for pain intensity and the Interpersonal Reactivity Index for empathic ability were also obtained. We found that women with PDM exhibited higher pain empathy compared with controls. The anterior insula and brain regions related to sensory discrimination with decreased gray matter volumes were not only shared but also acted as a mediator between pain intensity and pain empathy in PDM patients. In addition, the general linear modeling analysis revealed that long-term pain experience was a more important factor to pain empathy compared with pain intensity. This indicated that long-term pain may cause maladaptive brain structural plasticity, which may further affect psychological adjustment to bring patients more vivid pain when they witness suffering and distress in others.

Reduced pain perception in patients with schizophrenia; A missed case of hand fracture

Altered pain perception among patients with schizophrenia is often underrecognized in the medical community. The cause is not known, and medical professionals are not sure whether these patients experience less pain or are simply unable to express it. There are documented cases of patients with schizophrenia presenting to hospital settings with serious injuries without obvious (expected) pain. Research into the underlying cause(s) is underway; meanwhile, ensuring awareness of this issue among medical providers is of upmost importance. We report a case of a patient with schizophrenia who presented voluntarily to the emergency department (ED) with a hand fracture that went unrecognized in the ED and further discuss the implications of reduced pain perception. Additionally, we summarize existing hypotheses regarding the source of this reduced pain perception in this population.

Neural correlates of emotional processing in psychosis risk and onset - A systematic review and meta-analysis of fMRI studies

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The neural bases of altered emotion processing in psychosis are still unclear.

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Systematic review indicated widespread activation decreases to emotion in first-episode psychosis.

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Evidence in people at clinical high-risk for psychosis lacked convergence.

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These findings were corroborated by image-based meta-analyses.

Aberrant emotion processing is a well-established component of psychotic disorders and is already present at the first episode of psychosis (FEP). However, the role of emotion processing abnormalities in the emergence of psychosis and the underlying neurobiology remain unclear. Here, we systematically reviewed functional magnetic resonance studies that used emotion processing task paradigms in FEP patients, and in people at clinical high-risk for psychosis (CHRp). Image-based meta-analyses with Seed-based d Mapping on available studies (n = 6) were also performed. Compared to controls, FEP patients showed decreased neural responses to emotion, particularly in the amygdala and anterior cingulate cortex. There were no significant differences between CHRp subjects and controls, but a high degree of heterogeneity was identified across studies. The role of altered emotion processing in the early phase of psychosis may be clarified through more homogenous experimental designs, particularly in the CHRp population.

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.

Test-retest reliability of laser evoked pain perception and fMRI BOLD responses

Pain perception is a subjective experience and highly variable across time. Brain responses evoked by nociceptive stimuli are highly associated with pain perception and also showed considerable variability. To date, the test–retest reliability of laser-evoked pain perception and its associated brain responses across sessions remain unclear. Here, an experiment with a within-subject repeated-measures design was performed in 22 healthy volunteers. Radiant-heat laser stimuli were delivered on subjects’ left-hand dorsum in two sessions separated by 1–5 days. We observed that laser-evoked pain perception was significantly declined across sessions, coupled with decreased brain responses in the bilateral primary somatosensory cortex (S1), right primary motor cortex, supplementary motor area, and middle cingulate cortex. Intraclass correlation coefficients between the two sessions showed “fair” to “moderate” test–retest reliability for pain perception and brain responses. Additionally, we observed lower resting-state brain activity in the right S1 and lower resting-state functional connectivity between right S1 and dorsolateral prefrontal cortex in the second session than the first session. Altogether, being possibly influenced by changes of baseline mental state, laser-evoked pain perception and brain responses showed considerable across-session variability. This phenomenon should be considered when designing experiments for laboratory studies and evaluating pain abnormalities in clinical practice.

Barriers to Somatic Health Care for Persons With Severe Mental Illness in Belgium: A Qualitative Study of Patients' and Healthcare Professionals' Perspectives

BACKGROUND

A huge and still growing mortality gap between people with severe mental illness (SMI) and the general population exists. Physical illnesses, mainly cardiovascular diseases, substantially contribute to the high mortality rates in patients with SMI. Disparities in somatic health care access, utilisation, and provision contribute to these poor physical health outcomes.

METHODS

A qualitative study, using semi-structured interviews, was set up to explore SMI patients' and healthcare professionals' perspectives on somatic health care in different psychiatric settings of the three Belgian regions (Flanders, Brussels, Wallonia). Interviews were digitally recorded and transcribed prior to qualitative inductive thematic analysis, using Nvivo software. The COnsolidated criteria for REporting Qualitative research (COREQ) were used for reporting methods and findings.

RESULTS

Collaboration and information flows between psychiatric healthcare professionals, non-psychiatric healthcare professionals, and persons with SMI were troublesome. This seemed to be mainly due to stigma and prejudice and challenging communication and data transfer. Lack of sufficient training and experience to identify and treat somatic health problems in people with SMI (for psychiatrists and psychiatric nurses) and lack of psychiatric knowledge and feeling or sensitivity for psychiatric patients (for non-psychiatric healthcare professionals) further complicated adequate somatic health care. Finally, optimal somatic follow-up of patients with SMI was hampered by organisational problems (unavailability of equipment, unadapted infrastructure, understaffing, hospital pharmacy issues, and insufficient health promotion/lifestyle interventions), patient-related issues (unawareness of physical problems, non-adherence, need for accompaniment) and financial barriers.

CONCLUSION

There is an urgent need for integrated somatic and mental healthcare systems and a cultural change. Psychiatrists and primary care providers continue to consider the mental and physical health of their patients as mutually exclusive responsibilities due to a lack of sufficient training and experience, poor or absent liaison links, time constraints and organisational and financial barriers. Modifying these aspects will improve the quality of somatic health care for these vulnerable patients.

Differential Physical and Mental Benefits of Physiotherapy Program Among Patients With Schizophrenia and Healthy Controls Suggesting Different Physical Characteristics and Needs

In contrast to several other severe illnesses marked by inflammation and autoimmunity that now have potent and efficient treatments and even cures, schizophrenia (SCZ) is a disease still associated with poor outcome, incapacity, and social burden. Even after decades of research on the brain and behavior, this illness is still associated with profound effects on both mental health and physical health, with recent studies showing that treatment is more efficient when associating drugs with psychological and physical treatments. Most of the studies measured the effects of physical intervention compared with usual care and demonstrated a positive effect as an add-on treatment. What remains unclear is the different effects of the same intervention in normal subjects in a sample of patients with the illness. The study aimed to evaluate the effects of physical intervention over motor functional capacity and mental health in patients with SCZ compared with healthy controls (HC). The outcomes were (a) functional capacity [by 6-min walk test (6MWT)], (b) body flexibility index (Wells' bench), (c) disease severity [by Brief Psychiatric Rating Scale (BPRS)], (d) quality of life [by 36-Item Short Form (SF-36) questionnaire], and (e) physical activity [Simple Physical Activity Questionnaire (SIMPAQ)]. The intervention was associated with significant decrease of body mass index (BMI), blood pressure, disease severity, and improvement in daily life activities. Unexpectedly, it was observed that schizophrenics, compared with matched HC, were at a lower level of performance in the beginning, remained below HC over the studied time despite similar physical intervention, and had different changes. The intervention had lower effects over physical capacity and better effects over quality of life and disease severity. The results confirm previous studies comparing patients receiving physical intervention but suggest that they may receive different types of intervention, suited for their different baseline fitness, motivation, and capacity to engage in physical effort over sustained time. Additionally, they point to extended time of intervention of multidisciplinary treatment (physical and psychological-cognitive techniques) to improve outcomes in SCZ.

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.