Altered Behavioral and Autonomic Pain Responses in Alzheimer's Disease Are Associated with Dysfunctional Affective, Self-Reflective and Salience Network Resting-State Connectivity

Autonomic nervous system flexibility for understanding brain aging

A recent call was made for autonomic nervous system (ANS) measures as digital health markers for early detection of Alzheimer's disease and related dementia (AD/ADRD). Nevertheless, contradictory or inconclusive findings exist. To help advance understanding of ANS' role in dementia, we draw upon aging and dementia-related literature, and propose a framework that centers on the role of ANS flexibility to guide future work on application of ANS function to differentiating the degree and type of dementia-related brain pathologies. We first provide a brief review of literature within the past 10 years on ANS and dementia-related brain pathologies. Next, we present an ANS flexibility model, describing how the model can be applied to understand these brain pathologies, as well as differentiate or even be leveraged to modify typical brain aging and dementia. Lastly, we briefly discuss the implication of the model for understanding resilience and vulnerability to dementia-related outcomes.

Chronic pain in Alzheimer's disease: Endocannabinoid system

Chronic pain, one of the most common reasons adults seek medical care, has been linked to restrictions in mobility and daily activities, dependence on opioids, anxiety, depression, sleep deprivation, and reduced quality of life. Alzheimer's disease (AD), a devastating neurodegenerative disorder (characterized by a progressive impairment of cognitive functions) in the elderly, is often co-morbid with chronic pain. AD is one of the most common neurodegenerative disorders in the aged population. The reported prevalence of chronic pain is 45.8% of the 50 million people with AD. As the population ages, the number of older people who experience AD and chronic pain will also increase. The current treatment options for chronic pain are limited, often ineffective, and have associated side effects. This review summarizes the role of the endocannabinoid system in pain, its potential role in chronic pain in AD, and addresses gaps and future directions.

Feasibility, Acceptability, and Efficacy of Home-Based Transcranial Direct Current Stimulation on Pain in Older Adults with Alzheimer's Disease and Related Dementias: A Randomized Sham-Controlled Pilot Clinical Trial

Although transcranial direct current stimulation (tDCS) is emerging as a convenient pain relief modality for several chronic pain conditions, its feasibility, acceptability, and preliminary efficacy on pain in patients with Alzheimer's disease and related dementias (ADRD) have not been investigated. The purpose of this pilot study was to assess the feasibility, acceptability, and preliminary efficacy of 5, 20-min home-based tDCS sessions on chronic pain in older adults with ADRD. We randomly assigned 40 participants to active (n = 20) or sham (n = 20) tDCS. Clinical pain intensity was assessed using a numeric rating scale (NRS) with patients and a proxy measure (MOBID-2) with caregivers. We observed significant reductions of pain intensity for patients in the active tDCS group as reflected by both pain measures (NRS: Cohen's d = 0.69, p-value = 0.02); MOBID-2: Cohen's d = 1.12, p-value = 0.001). Moreover, we found home-based tDCS was feasible and acceptable intervention approach for pain in ADRD. These findings suggest the need for large-scale randomized controlled studies with larger samples and extended versions of tDCS to relieve chronic pain on the long-term for individuals with ADRD.

Increased pain unpleasantness and pain-related fMRI activation in the periaqueductal gray in Alzheimer's disease

Background

Pain continues to be underrecognized and undertreated in people with Alzheimer's disease (AD). The periaqueductal gray (PAG) is essential to pain processing and modulation yet is damaged by AD. While evidence exists of altered neural processing of pain in AD, there has not been a focused investigation of the PAG during pain in people with AD.

Purpose

To investigate the role of the PAG in sensory and affective pain processing for people living with AD.

Methods

Participants from a larger study completed pain psychophysics assessments and then a perceptually-matched heat pain task (warmth, mild, and moderate pain) during a functional MRI scan. In this cross-sectional study, we examined blood oxygenation level-dependent (BOLD) responses in the PAG and other pain-related regions in participants with AD (n = 18) and cognitively intact older adults (age- and sex-matched, n = 18). Associations of BOLD percent signal change and psychophysics were also examined.

Results

There were significant main effects of AD status on the temperature needed to reach each perception of warmth or pain, where people with AD reached higher temperatures. Furthermore, participants with AD rated mild and moderate pain as more unpleasant than controls. PAG BOLD activation was greater in AD relative to controls during warmth and mild pain percepts. No significant differences were found for moderate pain or in other regions of interest. Greater PAG activation during mild pain was associated with higher affective/unpleasantness ratings of mild pain in participants with AD but not in controls.

Conclusion

Results suggest a role for the PAG in altered pain responses in people with AD. The PAG is the primary source of endogenous opioid pain inhibition in the neuroaxis, thus, altered PAG function in AD suggests possible changes in descending pain inhibitory circuits. People with AD may have a greater risk of suffering from pain compared to cognitively intact older adults.

Documented nursing practices of pain assessment and management when communicating about pain in dementia care

AIM

To evaluate nurses' documented practice when communicating about pain for people with dementia in hospital.

DESIGN

Retrospective medical record review.

METHOD

Medical records were retrieved from four inpatient units in a district and a tertiary teaching hospital of people aged 65 years and over with documented dementia. Data were extracted on nurses' documented pain assessment and management. Pain frequency and association between patient self-report, pain scores, cognition levels and analgesics used during hospitalization were analysed using descriptive and inferential statistics. Multivariate regression examined patient characteristics, pain characteristics and length of hospital stay.

RESULTS

One-hundred patient records met the inclusion criteria between 1 January and 31 August 2017. Sixty-six percent of patients with dementia had pain documented at least once during hospitalization with 58% reported as moderate to severe pain intensity. Patients' pain severity during admission was associated with their length of hospital stay. Ninety-three percent of nurses used a self-reporting pain tool and 7% used an observational pain tool. Pain scores were not associated with patients' cognition level, nurses' pain reports or analgesic management.

CONCLUSION

Pain frequently occurs in people with dementia during hospitalization. Fragmented pain reporting influences the translation of pain messages. Disproportionate pain tool application and non-association between pain scores and analgesic management suggest a potential knowledge gap among nurses about the practical use of pain tools and practice gap between pain assessment and management in dementia care.

IMPACT

Pain was regularly assessed by nurses and implemented as a fifth vital sign for people with dementia in hospitals. However, the high frequency of pain affects care outcomes. Areas for improvement include nursing practice of pain assessment and management in dementia care in hospitals. Further understanding of the usefulness of pain tools and the efficacy of pain scores when communicating about pain in dementia care in hospitals is required.

A Cross-Sectional Study of Pain Sensitivity and Unpleasantness in People with Vascular Dementia

OBJECTIVE

Advanced age holds higher risk of both pain and dementia, with many studies finding dementia often heightens sensitivity to pain. VaD is the second most common type of dementia. Only a few observational or retrospective studies have examined pain responsiveness in VaD, suggesting it may increase pain unpleasantness (i.e., pain affect). This study compared thermal pain psychophysics between a cohort of vascular dementia (VaD) patients and healthy control (HC) subjects.

DESIGN

Single center, cross-sectional, between-subjects design.

SUBJECTS

Verbally communicative, probable VaD patients (N = 23) and age- and sex-matched HC (N = 23).

METHODS

A thermal psychophysics protocol assessed "mild pain" and "moderate pain" thresholds (oC temperature) and associated unpleasantness ratings (0-20 scale) in both VaD and HC groups. Psychophysics were compared between groups by way of a mixed-effects analysis, controlling for depressive symptoms.

RESULTS

There were no significant differences between groups for pain thresholds (main effect p = 0.086, Cohen's d: mild = 0.55, moderate = 0.27). However, unpleasantness ratings were higher in the VaD group compared to HC (main effect p = 0.003; mild pain p = 0.022, Cohen's d = 0.79; moderate pain p = 0.057, Cohen's d = 0.6).

CONCLUSIONS

These results are consistent with prior observational findings suggesting VaD may make patients more susceptible to pain, particularly its affective component.

Alzheimer's Disease Progressively Reduces Visual Functional Network Connectivity

Background:

Postmortem studies of brains with Alzheimer’s disease (AD) not only find amyloid-beta (Aβ) and neurofibrillary tangles (NFT) in the visual cortex, but also reveal temporally sequential changes in AD pathology from higher-order association areas to lower-order areas and then primary visual area (V1) with disease progression.

Objective:

This study investigated the effect of AD severity on visual functional network.

Methods:

Eight severe AD (SAD) patients, 11 mild/moderate AD (MAD), and 26 healthy senior (HS) controls undertook a resting-state fMRI (rs-fMRI) and a task fMRI of viewing face photos. A resting-state visual functional connectivity (FC) network and a face-evoked visual-processing network were identified for each group.

Results:

For the HS, the identified group-mean face-evoked visual-processing network in the ventral pathway started from V1 and ended within the fusiform gyrus. In contrast, the resting-state visual FC network was mainly confined within the visual cortex. AD disrupted these two functional networks in a similar severity dependent manner: the more severe the cognitive impairment, the greater reduction in network connectivity. For the face-evoked visual-processing network, MAD disrupted and reduced activation mainly in the higher-order visual association areas, with SAD further disrupting and reducing activation in the lower-order areas.

Conclusion:

These findings provide a functional corollary to the canonical view of the temporally sequential advancement of AD pathology through visual cortical areas. The association of the disruption of functional networks, especially the face-evoked visual-processing network, with AD severity suggests a potential predictor or biomarker of AD progression.

Anterior Cingulate Cortex Activity During Rest Is Related to Alterations in Pain Perception in Aging

Alterations in the affective component of pain perception are related to the development of chronic pain and may contribute to the increased vulnerability to pain observed in aging. The present study analyzed age-related changes in resting-state brain activity and their possible relation to an increased pain perception in older adults. For this purpose, we compared EEG current source density and fMRI functional-connectivity at rest in older (n = 20, 66.21 ± 3.08 years) and younger adults (n = 21, 20.71 ± 2.30 years) and correlated those brain activity parameters with pain intensity and unpleasantness ratings elicited by painful stimulation. We found an age-related increase in beta2 and beta3 activity in temporal, frontal, and limbic areas, and a decrease in alpha activity in frontal areas. Moreover, older participants displayed increased functional connectivity in the anterior cingulate cortex (ACC) and the insula with precentral and postcentral gyrus. Finally, ACC beta3 activity was positively correlated with pain intensity and unpleasantness ratings in older, and ACC-precentral/postcentral gyrus connectivity was positively correlated with unpleasantness ratings in older and younger participants. These results reveal that ACC resting-state hyperactivity is a stable trait of brain aging and may underlie their characteristic altered pain perception.

Pain processing in older adults with dementia-related cognitive impairment is associated with frontal neurodegeneration

Experimental pain research has shown that pain processing seems to be heightened in dementia. It is unclear which neuropathological changes underlie these alterations. This study examined whether differences in pressure pain sensitivity and endogenous pain inhibition (conditioned pain modulation (CPM)) between individuals with a dementia-related cognitive impairment (N=23) and healthy controls (N=35) are linked to dementia-related neurodegeneration. Pain was assessed via self-report ratings and by analyzing the facial expression of pain using the Facial Action Coding System. We found that cognitively impaired individuals show decreased CPM inhibition as assessed by facial responses compared to healthy controls, which was mediated by decreased gray matter volume in the medial orbitofrontal and anterior cingulate cortex in the patient group. This study confirms previous findings of intensified pain processing in dementia when pain is assessed using non-verbal responses. Our findings suggest that a loss of pain inhibitory functioning caused by structural changes in prefrontal areas might be one of the underlying mechanisms responsible for amplified pain responses in individuals with a dementia-related cognitive impairment.

Experimentally evoked pain in Alzheimer's disease

BACKGROUND

Pain continues to be underrecognized and undertreated in Alzheimer's disease (AD) while existing guidance about pain assessment and management in dementia is not widespread. Brain regions involved in pain processing and modulation are damaged during AD, and the pain experience in AD is not well understood. Experimental pain studies using psychophysics can further our understanding of the pain experience in AD, which may lead to improved assessment and management of pain in people living with AD.

OBJECTIVE

A systematic review was conducted to explicate the current understanding of experimentally evoked pain in AD from primary research using psychophysical methods.

DATA SOURCES

Peer-reviewed publications were found via PubMed, CINAHL, and PsycINFO. A total of 18 primary research, peer-reviewed full articles that met inclusion criteria were included, representing 929 total participants.

CONCLUSIONS

Experimentally evoked pain in people with AD demonstrates that despite cognitive impairment and a reduced ability to effectively communicate, individuals with AD experience pain similar to or more unpleasant than cognitively intact older adults. This may mean amplified pain unpleasantness in people with AD.

IMPLICATIONS FOR PRACTICE

Our current best practices need to be widely disseminated and put into clinical practice. Self-report of pain continues to be the gold standard, but it is ineffective for noncommunicative patients and those unable to understand pain scales or instructions because of memory/cognitive impairment. Instead, pain treatment should be ethically initiated based on patient reports and behaviors, caregiver/surrogate reports, review of the medical record for painful conditions, analgesic trials, and regular reassessments.

Policy Implications for Pain in Advanced Alzheimer's Disease

Untreated pain in people with Alzheimer's disease continues to be a serious public health problem. Pain is a subjective and complex experience that becomes increasingly challenging to assess as cognition declines. Our understanding of pain processing is incomplete, particularly for special populations such as people living with Alzheimer's disease, and especially in the advanced stages of the disease. Pain-processing networks in the brain are altered in Alzheimer's disease, yet evidence suggests people living with Alzheimer's disease do not experience less pain. Rather, their pain is not adequately recognized or treated. Although scholarly publications provide important assistance, recent widespread reports and guidelines do not include sufficient guidance, especially as Alzheimer's disease progresses to the last stages. Additionally, current pain measurements may not accurately evaluate pain in this condition, and the existing definitions of pain are not adequate when considering the effects of Alzheimer's disease on pain-processing in the brain. There is a need for new, widespread policies, guidelines, and definitions to help clinicians adequately manage pain in people with Alzheimer's disease. These will need to hinge on continued research because it remains unclear how Alzheimer's disease impacts central pain processing, pain expression, and communication of pain. In the meantime, policies and guidelines need to highlight current best practices as well as the fact that pain continues in Alzheimer's disease.

The Vagal Autonomic Pathway of COVID-19 at the Crossroad of Alzheimer's Disease and Aging: A Review of Knowledge

Coronavirus Disease 2019 (COVID-19) pandemic-triggered mortality is significantly higher in older than in younger populations worldwide. Alzheimer's disease (AD) is related to aging and was recently reported to be among the major risk factors for COVID-19 mortality in older people. The symptomatology of COVID-19 indicates that lethal outcomes of infection rely on neurogenic mechanisms. The present review compiles the available knowledge pointing to the convergence of COVID-19 complications with the mechanisms of autonomic dysfunctions in AD and aging. The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is prone to neuroinvasion from the lung along the vagus nerve up to the brainstem autonomic nervous centers involved in the coupling of cardiovascular and respiratory rhythms. The brainstem autonomic network allows SARS-CoV-2 to trigger a neurogenic switch to hypertension and hypoventilation, which may act in synergy with aging- and AD-induced dysautonomias, along with an inflammatory "storm". The lethal outcomes of COVID-19, like in AD and unhealthy aging, likely rely on a critical hypoactivity of the efferent vagus nerve cholinergic pathway, which is involved in lowering cardiovascular pressure and systemic inflammation tone. We further discuss the emerging evidence supporting the use of 1) the non-invasive stimulation of vagus nerve as an additional therapeutic approach for severe COVID-19, and 2) the demonstrated vagal tone index, i.e., heart rate variability, via smartphone-based applications as a non-serological low-cost diagnostic of COVID-19. These two well-known medical approaches are already available and now deserve large-scale testing on human cohorts in the context of both AD and COVID-19.

Dysautonomia in Alzheimer's Disease

Alzheimer's disease is the most common neurodegenerative disorder, and its prevalence increases with age. Although there is a large amount of scientific literature focusing on Alzheimer's disease cardinal cognitive features, autonomic nervous system dysfunction remains understudied despite being common in the elderly. In this article, we reviewed the evidence for autonomic nervous system involvement in Alzheimer's disease. We identified four major potential causes for dysautonomia in Alzheimer's disease, out of which two are well-studied (comorbidities and medication) and two are rather hypothetical (Alzheimer's pathology and brain co-pathology). Although there appears to be some evidence linking Alzheimer's disease pathology to autonomic nervous system dysfunction, there is an important gap between two types of studies; histopathologic studies do not address dysautonomia manifestations, whereas clinical studies do not employ histopathologic diagnostic confirmation. Moreover, brain co-pathology is emerging as an important confounding factor. Therefore, we consider the correlation between dysautonomia and Alzheimer's disease to be an open question that needs further study. Nevertheless, given its impact on morbidity and mortality, we emphasize the importance of assessing autonomic dysfunction in patients with Alzheimer clinical syndrome.

Sex Differences in the Psychophysical Response to Contact Heat in Moderate Cognitive Impairment Alzheimer's Disease: A Cross-Sectional Brief Report

Background:

People with Alzheimer’s disease (AD) report pain less frequently and receive less pain medication than people without AD. Recent studies have begun to elucidate how pain may be altered in those with AD. However, potential sex differences in pain responsiveness have never been explored in these patients. It is unclear whether sex differences found in prior studies of healthy young and older individuals extend to people with AD.

Objective:

The purpose of this study was to examine sex differences in the psychophysical response to experimental thermal pain in people with AD.

Methods:

Cross-sectional analysis of 14 male and 14 female age-matched (≥65 years of age, median = 74) and AD severity-matched (Mini-Mental State Exam score <24, median = 16) communicative people who completed thermal psychophysics.

Results:

There was a statistically significant main effect of sex for both temperature and unpleasantness ratings that persisted after controlling for average and current pain (mixed-effects general liner model: temperature: p = 0.004, unpleasantness: p < 0.001). Females reported sensing mild pain and moderate pain percepts at markedly lower temperatures than did males (mild: Cohen’s d = 0.72, p = 0.051, moderate: Cohen’s d = 0.80, p = 0.036). By contrast, males rated mild and moderate thermal pain stimuli as more unpleasant than did females (mild: Cohen’s d = 0.80, p = 0.072, moderate: Cohen’s d = 1.32, p = 0.006). There were no statistically significant correlations of temperature with perceived unpleasantness for mild or moderate pain (r_s = 0.29 and r_s = 0.20 respectively, p > 0.05).

Conclusions:

Results suggest experimental pain-related sex differences persist in older adults with AD in a different manner than those previously demonstrated in cognitively intact older adults. These findings could potentially aid in developing targeted pain management approaches in this vulnerable population. Further studies are warranted to replicate the findings from this pilot work.

A Technical Note on the PainChek™ System: A Web Portal and Mobile Medical Device for Assessing Pain in People With Dementia

Background: Pain in dementia is predominant particularly in the advanced stages or in those who are unable to verbalize. Uncontrolled pain alters the course of behaviors in patients with dementia making them perturbed, unsettled, and devitalized. Current measures of assessing pain in this population group are inadequate and underutilized in clinical practice because they lack systematic evaluation and innovative design.

Objective: To describe a novel method and system of pain assessment using a combination of technologies: automated facial recognition and analysis (AFRA), smart computing, affective computing, and cloud computing (Internet of Things) for people with advanced dementia.

Methods and Results: Cognification and affective computing were used to conceptualize the system. A computerized clinical system was developed to address the challenging problem of identifying pain in non-verbal patients with dementia. The system is composed of a smart device enabled app (App) linked to a web admin portal (WAP). The App “PainChek™” uses AFRA to identify facial action units indicative of pain presence, and user-fed clinical information to calculate a pain intensity score. The App has various functionalities including: pain assessment, pain monitoring, patient profiling, and data synchronization (into the WAP). The WAP serves as a database that collects the data obtained through the App in the clinical setting. These technologies can assist in addressing the various characteristics of pain (e.g., subjectivity, multidimensionality, and dynamicity). With over 750 paired assessments conducted, the App has been validated in two clinical studies (n = 74, age: 60–98 y), which showed sound psychometric properties: excellent concurrent validity (r = 0.882–0.911), interrater reliability (Kw = 0.74–0.86), internal consistency (α = 0.925–0.950), and excellent test-retest reliability (ICC = 0.904), while it possesses good predictive validity and discriminant validity. Clinimetric data revealed high accuracy (95.0%), sensitivity (96.1%), and specificity (91.4%) as well as excellent clinical utility (0.95).

Conclusions: PainChek™ is a comprehensive and evidence-based pain management system. This novel approach has the potential to transform pain assessment in people who are unable to verbalize because it can be used by clinicians and carers in everyday clinical practice.

The tetrapartite synapse: a key concept in the pathophysiology of schizophrenia

Growing evidence points to synaptic pathology as a core component of the pathophysiology of schizophrenia (SZ). Significant reductions of dendritic spine density and altered expression of their structural and molecular components have been reported in several brain regions, suggesting a deficit of synaptic plasticity. Regulation of synaptic plasticity is a complex process, one that requires not only interactions between pre- and post-synaptic terminals, but also glial cells and the extracellular matrix (ECM). Together, these elements are referred to as the ‘tetrapartite synapse’, an emerging concept supported by accumulating evidence for a role of glial cells and the extracellular matrix in regulating structural and functional aspects of synaptic plasticity. In particular, chondroitin sulfate proteoglycans (CSPGs), one of the main components of the ECM, have been shown to be synthesized predominantly by glial cells, to form organized perisynaptic aggregates known as perineuronal nets (PNNs), and to modulate synaptic signaling and plasticity during postnatal development and adulthood. Notably, recent findings from our group and others have shown marked CSPG abnormalities in several brain regions of people with SZ. These abnormalities were found to affect specialized ECM structures, including PNNs, as well as glial cells expressing the corresponding CSPGs. The purpose of this review is to bring forth the hypothesis that synaptic pathology in SZ arises from a disruption of the interactions between elements of the tetrapartite synapse.