Neuropathology of depression in non-demented older adults: A large postmortem study of 741 individuals

Causes of death in individuals with lifetime major depression: a comprehensive machine learning analysis from a community-based autopsy center

BACKGROUND

Depression can be associated with increased mortality and morbidity, but no studies have investigated the specific causes of death based on autopsy reports. Autopsy studies can yield valuable and detailed information on pathological ailments or underreported conditions. This study aimed to compare autopsy-confirmed causes of death (CoD) between individuals diagnosed with major depressive disorder (MDD) and matched controls. We also analyzed subgroups within our MDD sample, including late-life depression and recurrent depression. We further investigated whether machine learning (ML) algorithms could distinguish MDD and each subgroup from controls based on their CoD.

METHODS

We conducted a comprehensive analysis of CoD in individuals who died from nontraumatic causes. The diagnosis of lifetime MDD was ascertained based on the DSM-5 criteria using information from a structured interview with a knowledgeable informant. Eleven established ML algorithms were used to differentiate MDD individuals from controls by simultaneously analyzing different disease category groups to account for multiple tests. The McNemar test was further used to compare paired nominal data.

RESULTS

The initial dataset included records of 1,102 individuals, among whom 232 (21.1%) had a lifetime diagnosis of MDD. Each MDD individual was strictly paired with a control non-psychiatric counterpart. In the MDD group, the most common CoD were circulatory (67.2%), respiratory (13.4%), digestive (6.0%), and cancer (5.6%). Despite employing a range of ML models, we could not find distinctive CoD patterns that could reliably distinguish individuals with MDD from individuals in the control group (average accuracy: 50.6%; accuracy range: 39-59%). These findings were consistent even when considering factors within the MDD group, such as late-life or recurrent MDD. When comparing groups with paired nominal tests, no differences were found for circulatory (p=0.450), respiratory (p=0.790), digestive (p=1.000), or cancer (p=0.855) CoD.

CONCLUSIONS

Our analysis revealed that autopsy-confirmed CoD exhibited remarkable similarity between individuals with depression and their matched controls, underscoring the existing heterogeneity in the literature. Future research should prioritize more severe manifestations of depression and larger sample sizes, particularly in the context of CoD related to cancer.

Clinical presentations and diagnostic application of proposed biomarkers in psychiatric-onset prodromal dementia with Lewy bodies

Research criteria for the diagnosis of prodromal dementia with Lewy bodies (DLB) include three clinical subtypes: mild cognitive impairment with Lewy bodies (MCI-LB), delirium-onset prodromal DLB, and psychiatric-onset prodromal DLB. Late-onset psychiatric manifestations are at a higher risk of developing dementia, but its relation to prodromal DLB remains unclear. In addition to the risk of severe antipsychotic hypersensitivity reactions, accurate discrimination from non-DLB cases is important due to the potential differences in management and prognosis. This article aims to review a rapidly evolving psychiatric topic and outline clinical pictures of psychiatric-onset prodromal DLB, including the proposed biomarker findings of MCI-LB: polysomnography-confirmed rapid eye movement sleep behaviour disorder, cardiac [123I]metaiodobenzylguanidine scintigraphy, and striatal dopamine transporter imaging. We first reviewed clinical pictures of patients with autopsy-confirmed DLB. Regarding clinical reports, we focused on the patients who predominantly presented with psychiatric manifestations and subsequently developed DLB. Thereafter, we reviewed clinical studies regarding the diagnostic applications of the proposed biomarkers to patients with late-onset psychiatric disorders. Clinical presentations were mainly late-onset depression and psychosis; however, other clinical manifestations were also reported. Psychotropic medications before a DLB diagnosis may cause extrapyramidal signs, and potentially influences the proposed biomarker findings. These risks complicate clinical manifestation interpretation during the management of psychiatric symptoms. Longitudinal follow-up studies with standardised evaluations until conversion to DLB are needed to investigate the temporal trajectories of core features and proposed biomarker findings. In patients with late-onset psychiatric disorders, identification of patients with psychiatric-onset prodromal DLB provides the opportunity to better understanding the distinct prognostic subgroup that is at great risk of incident dementia. Advances in the establishment of direct biomarkers for the detection of pathological α-synuclein may encourage reorganising the phenotypic variability of prodromal DLB.

Contributions of loneliness to cognitive impairment and dementia in older adults are independent of other risk factors and Alzheimer's pathology: a narrative review

Loneliness significantly contributes to cognitive impairment and dementia in older adults. Loneliness is a distressing feeling resulting from a perceived lack of social connection (i.e., a discrepancy between desired and actual social relationships), while social isolation is a related term that can be defined by number and type of social relationships. Importantly, loneliness is distinct from social isolation in that it is associated with a distressing self-perception. The primary focus of this narrative review is the impact of chronic loneliness on cognitive impairment and dementia among older adults. Loneliness has a significant association with many factors that are related to worse cognition, and therefore we include discussion on health, mental health, as well as the physiological effects of loneliness, neuropathology, and potential treatments. Loneliness has been shown to be related to development of dementia with a hazard ratio (HR) risk comparable to having a single APOE4 gene. The relationship of dementia to loneliness appears to be at least partially independent of other known dementia risk factors that are possibly associated with loneliness, such as depression, educational status, social isolation, and physical activity. Episodic memory is not consistently impacted by loneliness, which would be more typically impaired if the mild cognitive impairment (MCI) or dementia was due to Alzheimer's disease (AD) pathology. In addition, the several longitudinal studies that included neuropathology showed no evidence for a relationship between loneliness and AD neuropathology. Loneliness may decrease resilience, or produce greater cognitive change associated with the same level of AD neuropathology. Intervention strategies to decrease loneliness in older adults have been developed but need to consider key treatment targets beyond social isolation. Loneliness needs to be assessed in all studies of cognitive decline in elders, since it significantly contributes to the variance of cognitive function. It will be useful to better define the underlying mechanism of loneliness effects on cognition to determine if it is similar to other psychological factors related to excessive stress reactivity, such as neuroticism or even depression, which are also associated with cognitive decline. It is important from a health perspective to develop better strategies to decrease loneliness in older adults.

Distinguishing features of depression in dementia from primary psychiatric disease

Depression is a common and devastating neuropsychiatric symptom in the elderly and in patients with dementia. In particular, nearly 80% of patients with Alzheimer's Disease dementia experience depression during disease development and progression. However, it is unknown whether the depression in patients with dementia shares the same molecular mechanisms as depression presenting as primary psychiatric disease or occurs and persists through alternative mechanisms. In this review, we discuss how the clinical presentation and treatment differ between depression in dementia and as a primary psychiatric disease, with a focus on major depressive disorder. Then, we hypothesize several molecular mechanisms that may be unique to depression in dementia such as neuropathological changes, inflammation, and vascular events. Finally, we discuss existing issues and future directions for investigation and treatment of depression in dementia.

The clinical phenotype of psychiatric-onset prodromal dementia with Lewy bodies: a scoping review

BACKGROUND

Recent consensus research criteria have identified a 'psychiatric onset' form of prodromal dementia with Lewy bodies (DLB) characterised by prominent late-onset psychiatric symptoms. Although recognised as important to raise the index of diagnostic suspicion, evidence regarding this cohort was deemed too limited to impose formal criteria. We reviewed the published literature on psychiatric-onset DLB to identify key clinical characteristics and evidence gaps to progress our understanding of this entity.

METHODS

Medline, PubMed and Embase were searched for relevant articles containing longitudinal follow-up of patients initially presenting with a psychiatric illness who subsequently developed DLB according to the diagnostic criteria available at the time.

RESULTS

Two cohort studies (18 and 21 patients) along with 12 case series (13 cases) were identified totalling 52 patients (63% female). Initial psychiatric presentation occurred at a mean of 63 years (range 53-88), with depression being the most frequently reported psychiatric presentation (88%). Psychotic presentations were less common on presentation (11%) but became more prevalent throughout the prodromal period before the diagnosis of DLB (83%). Relapses of the psychiatric disease were common occurring in 94% (32/34) of patients. Parkinsonism, cognitive fluctuations, visual hallucinations, and REM sleep behaviour disorder were uncommonly reported at initial presentation (3.8%).

CONCLUSIONS

Psychiatric-onset DLB is characterized by a female predominant relapsing-remitting psychiatric illness presenting with affective symptoms but later developing psychotic features prior to the onset of DLB. Additional prospective studies including other neurodegenerative cohorts with harmonised assessments are required to inform definitive diagnostic criteria for this condition.

Prevalence and incidence of depressive symptoms and diagnosis of depression as associated with elevated amyloid among Medicare beneficiaries with cognitive impairment

BACKGROUND

Depression and cognitive impairment commonly co-occur, and it has been hypothesized that the two share pathological processes. Our objective for this study was to determine the relationship between elevated β-amyloid level and the prevalence and incidence of depressive symptoms and diagnosed depression over two years among fee-for-service Medicare beneficiaries with cognitive impairment.

METHODS

We utilized data from the CARE-IDEAS cohort study (N = 2078) including two measures of depressive symptoms (PHQ-2) and administrative claims data to identify pre-scan and incident depression diagnosis in subsample of fee-for-service Medicare beneficiaries (N = 1443). We used descriptive statistics and Poisson regression models with robust covariance.

RESULTS

Beneficiaries whose scan results indicated not-elevated β-amyloid were significantly more likely to have been diagnosed with depression pre-scan (46.4 % vs. 33.1 %). There was no significant association between elevated amyloid and the incidence of depressive symptoms or diagnosed depression.

LIMITATIONS

The sample was limited to Medicare beneficiaries with cognitive impairment. Race/ethnic composition and education levels were not representative of the general population and there was substantial loss to follow-up. Mixed depressive / anxious episodes were captured as diagnoses of depression, potentially overestimating depression in this population.

CONCLUSIONS

There was a high prevalence and incidence of diagnosed depression in this cohort of Medicare beneficiaries, but the incidence of depressive symptoms and diagnosed depression was not associated with elevated β-amyloid.

Neurodegenerative pathologies associated with behavioral and psychological symptoms of dementia in a community-based autopsy cohort

In addition to the memory disorders and global cognitive impairment that accompany neurodegenerative diseases, behavioral and psychological symptoms of dementia (BPSD) commonly impair quality of life and complicate clinical management. To investigate clinical-pathological correlations of BPSD, we analyzed data from autopsied participants from the community-based University of Kentucky Alzheimer's Disease Research Center longitudinal cohort (n = 368 research volunteers met inclusion criteria, average age at death 85.4 years). Data assessing BPSD were obtained approximately annually, including parameters for agitation, anxiety, apathy, appetite problems, delusions, depression, disinhibition, hallucinations, motor disturbance, and irritability. Each BPSD was scored on a severity scale (0-3) via the Neuropsychiatric Inventory Questionnaire (NPI-Q). Further, Clinical Dementia Rating (CDR)-Global and -Language evaluations (also scored on 0-3 scales) were used to indicate the degree of global cognitive and language impairment. The NPI-Q and CDR ratings were correlated with neuropathology findings at autopsy: Alzheimer's disease neuropathological changes (ADNC), neocortical and amygdala-only Lewy bodies (LBs), limbic predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC), primary age-related tauopathy (PART), hippocampal sclerosis, and cerebrovascular pathologies. Combinations of pathologies included the quadruple misfolding proteinopathy (QMP) phenotype with co-occurring ADNC, neocortical LBs, and LATE-NC. Statistical models were used to estimate the associations between BPSD subtypes and pathologic patterns. Individuals with severe ADNC (particularly those with Braak NFT stage VI) had more BPSD, and the QMP phenotype was associated with the highest mean number of BPSD symptoms: > 8 different BPSD subtypes per individual. Disinhibition and language problems were common in persons with severe ADNC but were not specific to any pathology. "Pure" LATE-NC was associated with global cognitive impairment, apathy, and motor disturbance, but again, these were not specific associations. In summary, Braak NFT stage VI ADNC was strongly associated with BPSD, but no tested BPSD subtype was a robust indicator of any particular "pure" or mixed pathological combination.

The heterogeneity of late-life depression and its pathobiology: a brain network dysfunction disorder

Depression is frequent in older individuals and is often associated with cognitive impairment and increasing risk of subsequent dementia. Late-life depression (LLD) has a negative impact on quality of life, yet the underlying pathobiology is still poorly understood. It is characterized by considerable heterogeneity in clinical manifestation, genetics, brain morphology, and function. Although its diagnosis is based on standard criteria, due to overlap with other age-related pathologies, the relationship between depression and dementia and the relevant structural and functional cerebral lesions are still controversial. LLD has been related to a variety of pathogenic mechanisms associated with the underlying age-related neurodegenerative and cerebrovascular processes. In addition to biochemical abnormalities, involving serotonergic and GABAergic systems, widespread disturbances of cortico-limbic, cortico-subcortical, and other essential brain networks, with disruption in the topological organization of mood- and cognition-related or other global connections are involved. Most recent lesion mapping has identified an altered network architecture with "depressive circuits" and "resilience tracts", thus confirming that depression is a brain network dysfunction disorder. Further pathogenic mechanisms including neuroinflammation, neuroimmune dysregulation, oxidative stress, neurotrophic and other pathogenic factors, such as β-amyloid (and tau) deposition are in discussion. Antidepressant therapies induce various changes in brain structure and function. Better insights into the complex pathobiology of LLD and new biomarkers will allow earlier and better diagnosis of this frequent and disabling psychopathological disorder, and further elucidation of its complex pathobiological basis is warranted in order to provide better prevention and treatment of depression in older individuals.

Sleep matters: Neurodegeneration spectrum heterogeneity, combustion and friction ultrafine particles, industrial nanoparticle pollution, and sleep disorders-Denial is not an option

Sustained exposures to ubiquitous outdoor/indoor fine particulate matter (PM_2.5), including combustion and friction ultrafine PM (UFPM) and industrial nanoparticles (NPs) starting in utero, are linked to early pediatric and young adulthood aberrant neural protein accumulation, including hyperphosphorylated tau (p-tau), beta-amyloid (Aβ_{1 - 42}), α-synuclein (α syn) and TAR DNA-binding protein 43 (TDP-43), hallmarks of Alzheimer's (AD), Parkinson's disease (PD), frontotemporal lobar degeneration (FTLD), and amyotrophic lateral sclerosis (ALS). UFPM from anthropogenic and natural sources and NPs enter the brain through the nasal/olfactory pathway, lung, gastrointestinal (GI) tract, skin, and placental barriers. On a global scale, the most important sources of outdoor UFPM are motor traffic emissions. This study focuses on the neuropathology heterogeneity and overlap of AD, PD, FTLD, and ALS in older adults, their similarities with the neuropathology of young, highly exposed urbanites, and their strong link with sleep disorders. Critical information includes how this UFPM and NPs cross all biological barriers, interact with brain soluble proteins and key organelles, and result in the oxidative, endoplasmic reticulum, and mitochondrial stress, neuroinflammation, DNA damage, protein aggregation and misfolding, and faulty complex protein quality control. The brain toxicity of UFPM and NPs makes them powerful candidates for early development and progression of fatal common neurodegenerative diseases, all having sleep disturbances. A detailed residential history, proximity to high-traffic roads, occupational histories, exposures to high-emission sources (i.e., factories, burning pits, forest fires, and airports), indoor PM sources (tobacco, wood burning in winter, cooking fumes, and microplastics in house dust), and consumption of industrial NPs, along with neurocognitive and neuropsychiatric histories, are critical. Environmental pollution is a ubiquitous, early, and cumulative risk factor for neurodegeneration and sleep disorders. Prevention of deadly neurological diseases associated with air pollution should be a public health priority.

Depression Pathophysiology: Astrocyte Mitochondrial Melatonergic Pathway as Crucial Hub

Major depressive disorder (MDD) is widely accepted as having a heterogenous pathophysiology involving a complex mixture of systemic and CNS processes. A developmental etiology coupled to genetic and epigenetic risk factors as well as lifestyle and social process influences add further to the complexity. Consequently, antidepressant treatment is generally regarded as open to improvement, undoubtedly as a consequence of inappropriately targeted pathophysiological processes. This article reviews the diverse array of pathophysiological processes linked to MDD, and integrates these within a perspective that emphasizes alterations in mitochondrial function, both centrally and systemically. It is proposed that the long-standing association of MDD with suppressed serotonin availability is reflective of the role of serotonin as a precursor for the mitochondrial melatonergic pathway. Astrocytes, and the astrocyte mitochondrial melatonergic pathway, are highlighted as crucial hubs in the integration of the wide array of biological underpinnings of MDD, including gut dysbiosis and permeability, as well as developmental and social stressors, which can act to suppress the capacity of mitochondria to upregulate the melatonergic pathway, with consequences for oxidant-induced changes in patterned microRNAs and subsequent patterned gene responses. This is placed within a development context, including how social processes, such as discrimination, can physiologically regulate a susceptibility to MDD. Future research directions and treatment implications are derived from this.

The pathobiological basis of depression in Parkinson disease: challenges and outlooks

Depression, with an estimated prevalence of about 40% is a most common neuropsychiatric disorder in Parkinson disease (PD), with a negative impact on quality of life, cognitive impairment and functional disability, yet the underlying neurobiology is poorly understood. Depression in PD (DPD), one of its most common non-motor symptoms, can precede the onset of motor symptoms but can occur at any stage of the disease. Although its diagnosis is based on standard criteria, due to overlap with other symptoms related to PD or to side effects of treatment, depression is frequently underdiagnosed and undertreated. DPD has been related to a variety of pathogenic mechanisms associated with the underlying neurodegenerative process, in particular dysfunction of neurotransmitter systems (dopaminergic, serotonergic and noradrenergic), as well as to disturbances of cortico-limbic, striato-thalamic-prefrontal, mediotemporal-limbic networks, with disruption in the topological organization of functional mood-related, motor and other essential brain network connections due to alterations in the blood-oxygen-level-dependent (BOLD) fluctuations in multiple brain areas. Other hypothetic mechanisms involve neuroinflammation, neuroimmune dysregulation, stress hormones, neurotrophic, toxic or metabolic factors. The pathophysiology and pathogenesis of DPD are multifactorial and complex, and its interactions with genetic factors, age-related changes, cognitive disposition and other co-morbidities awaits further elucidation.

The enigma of vascular depression in old age: a critical update

Depression is common in older individuals and is associated with high disability and increased mortality, yet the factors predicting late-life depression (LLD) are poorly understood. The relationship between of depressive disorder, age- and disease-related processes have generated pathogenic hypotheses and provided new treatment options. LLD syndrome is often related to a variety of vascular mechanisms, in particular hypertension, cerebral small vessel disease, white matter lesions, subcortical vascular impairment, and other processes (e.g., inflammation, neuroimmune regulatory dysmechanisms, neurodegenerative changes, amyloid accumulation) that may represent etiological factors by affecting frontolimbic and other neuronal networks predisposing to depression. The "vascular depression" hypothesis suggests that cerebrovascular disease (CVD) and vascular risk factors may predispose, induce or perpetuate geriatric depressive disorders. It is based on the presence of various cerebrovascular risk factors in many patients with LLD, its co-morbidity with cerebrovascular lesions, and the frequent development of depression after stroke. Other findings related to vascular depression are atrophy of the medial temporal cortex or generalized cortical atrophy that are usually associated with cognitive impairment. Other pathogenetic hypotheses of LLD, such as metabolic or inflammatory ones, are briefly discussed. Treatment planning should consider there may be a modest response to antidepressants, but several evidence-based and novel treatment options for LLD exist, such as electroconvulsive therapy, transcranial magnetic stimulation, neurobiology-based psychotherapy, as well as antihypertension and antiinflammatory drugs. However, their effectiveness needs further investigation, and new methodologies for prevention and treatment of depression in older individuals should be developed.