Comparisons between SPECT and quantitative EEG measures of cortical impairment in mild to moderate Alzheimer's disease

EEG alterations during wake and sleep in mild cognitive impairment and Alzheimer's disease

Patients with Alzheimer's disease (AD) undergo a slowing of waking electroencephalographic (EEG) rhythms since prodromal stages, which could be ascribed to poor sleep quality. We examined the relationship between wake and sleep alterations by assessing EEG activity during sleep and (pre-sleep/post-sleep) wakefulness in AD, mild cognitive impairment (MCI) and healthy controls. AD and MCI show high sleep latency and less slow-wave sleep. Reduced sigma activity characterizes non-rapid eye movement (NREM) sleep, reflecting sleep spindles loss. The EEG slowing characterizes REM sleep and wakefulness of AD and MCI, with strong correlations among the two phenomena suggesting common neuropathological mechanisms. Evening-to-morning variations in waking EEG revealed the gradual disappearance in MCI and AD of overnight changes in delta activity, indicating a progressive decay of sleep restorative functions on diurnal activity that correlates with the impairment of sleep high-frequency activity in AD. Our findings support a linkage between wake and sleep alterations, and the importance of sleep-related processes in Alzheimer's disease progression.

Combining SPECT and Quantitative EEG Analysis for the Automated Differential Diagnosis of Disorders with Amnestic Symptoms

Single photon emission computed tomography (SPECT) and Electroencephalography (EEG) have become established tools in routine diagnostics of dementia. We aimed to increase the diagnostic power by combining quantitative markers from SPECT and EEG for differential diagnosis of disorders with amnestic symptoms. We hypothesize that the combination of SPECT with measures of interaction (connectivity) in the EEG yields higher diagnostic accuracy than the single modalities. We examined 39 patients with Alzheimer's dementia (AD), 69 patients with depressive cognitive impairment (DCI), 71 patients with amnestic mild cognitive impairment (aMCI), and 41 patients with amnestic subjective cognitive complaints (aSCC). We calculated 14 measures of interaction from a standard clinical EEG-recording and derived graph-theoretic network measures. From regional brain perfusion measured by 99mTc-hexamethyl-propylene-aminoxime (HMPAO)-SPECT in 46 regions, we calculated relative cerebral perfusion in these patients. Patient groups were classified pairwise with a linear support vector machine. Classification was conducted separately for each biomarker, and then again for each EEG- biomarker combined with SPECT. Combination of SPECT with EEG-biomarkers outperformed single use of SPECT or EEG when classifying aSCC vs. AD (90%), aMCI vs. AD (70%), and AD vs. DCI (100%), while a selection of EEG measures performed best when classifying aSCC vs. aMCI (82%) and aMCI vs. DCI (90%). Only the contrast between aSCC and DCI did not result in above-chance classification accuracy (60%). In general, accuracies were higher when measures of interaction (i.e., connectivity measures) were applied directly than when graph-theoretical measures were derived. We suggest that quantitative analysis of EEG and machine-learning techniques can support differentiating AD, aMCI, aSCC, and DCC, especially when being combined with imaging methods such as SPECT. Quantitative analysis of EEG connectivity could become an integral part for early differential diagnosis of cognitive impairment.

Brain perfusion during rapid-eye-movement sleep successfully identifies amnestic mild cognitive impairment

INTRODUCTION

Prodromal markers of Alzheimer's disease (AD) have been derived from wakefulness. However, brain perfusion during rapid-eye movement (REM) sleep could be a sensitive marker of amnestic mild cognitive impairment (aMCI), as activation of REM sleep relies more on the cholinergic system.

METHODS

Eight subjects with aMCI, and 16 controls, underwent two single-photon emission computed tomography (SPECT) scans with tracer injected during REM sleep then wakefulness.

RESULTS

Perfusion in the anterior cingulate cortex was significantly decreased in aMCI cases compared to controls for both conditions. That defect was much larger and more severe in REM sleep (1795 voxels) compared to wakefulness (398 voxels), and extended to the middle cingulate cortex and the olfactory cortex. Hypoperfusion in the anterior cingulate cortex during REM sleep allowed better classification than hypoperfusion found in wakefulness (93.8 vs 81.3%).

CONCLUSION

REM sleep imaging is a valuable tool with which to identify individuals at risk of developing AD.

Quantitative EEG of Rapid-Eye-Movement Sleep: A Marker of Amnestic Mild Cognitive Impairment

The basal forebrain cholinergic system, which is impaired in early Alzheimer's disease, is more crucial for the activation of rapid-eye-movement (REM) sleep electroencephalogram (EEG) than it is for wakefulness. Quantitative EEG from REM sleep might thus provide an earlier and more accurate marker of the development of Alzheimer's disease in subjects with mild cognitive impairment (MCI) subjects than that from wakefulness. To assess the superiority of the REM sleep EEG as a screening tool for preclinical Alzheimer's disease, 22 subjects with amnestic MCI (a-MCI; 63.9±7.7 years), 10 subjects with nonamnestic MCI (na-MCI; 64.1±4.5 years) and 32 controls (63.7±6.6 years) participated in the study. Spectral analyses of the waking EEG and REM sleep EEG were performed and the [(delta+theta)/(alpha+beta)] ratio was used to assess between-group differences in EEG slowing. The a-MCI subgroup showed EEG slowing in frontal lateral regions compared to both na-MCI and control groups. This EEG slowing was present in wakefulness (compared to controls) but was much more prominent in REM sleep. Moreover, the comparison between amnestic and nonamnestic subjects was found significant only for the REM sleep EEG. There was no difference in EEG power ratio between na-MCI and controls for any of the 7 cortical regions studied. These findings demonstrate the superiority of the REM sleep EEG in the discrimination between a-MCI and both na-MCI and control subjects.

The utility of EEG in dementia: a clinical perspective

BACKGROUND

Despite being simple and cheap, the EEG is not often used in clinical practice.

METHODOLOGY

Literature search using PUBMED and Medline.

RESULTS

Quantitative EEG can help to identify mild dementia and mild cognitive impairment and can increase diagnostic accuracy when used with other imaging techniques. EEG helps differentiate organic from functional brain disease and predict response to cholinesterase inhibitors and is central in the diagnosis of Creutzfeldt Jacob disease. The accuracy of EEG may be greater than that of CT or MRI scans alone.

DISCUSSION

Quantitative EEG may save on specialist interpretation time and enable more routine use of EEG in diagnosis and care. More widespread use of EEG's is indicated. Agreement on the parameters that are best measured on qEEG is still awaited.

EEG dynamics in patients with Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by cognitive and intellectual deficits and behavior disturbance. The electroencephalogram (EEG) has been used as a tool for diagnosing AD for several decades. The hallmark of EEG abnormalities in AD patients is a shift of the power spectrum to lower frequencies and a decrease in coherence of fast rhythms. These abnormalities are thought to be associated with functional disconnections among cortical areas resulting from death of cortical neurons, axonal pathology, cholinergic deficits, etc. This article reviews main findings of EEG abnormalities in AD patients obtained from conventional spectral analysis and nonlinear dynamical methods. In particular, nonlinear alterations in the EEG of AD patients, i.e. a decreased complexity of EEG patterns and reduced information transmission among cortical areas, and their clinical implications are discussed. For future studies, improvement of the accuracy of differential diagnosis and early detection of AD based on multimodal approaches, longitudinal studies on nonlinear dynamics of the EEG, drug effects on the EEG dynamics, and linear and nonlinear functional connectivity among cortical regions in AD are proposed to be investigated. EEG abnormalities of AD patients are characterized by slowed mean frequency, less complex activity, and reduced coherences among cortical regions. These abnormalities suggest that the EEG has utility as a valuable tool for differential and early diagnosis of AD.

Sleep and quantitative EEG in neurodegenerative disorders

This paper reviews current knowledge on sleep problems, sleep architecture changes and quantitative EEG alteration brought on by various neurodegenerative diseases, such as Alzheimer's disease (AD), progressive supranuclear palsy (PSP), REM sleep behavior disorder (RBD), Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy MSA, Huntington's disease and Creutzfeldt-Jakob disease, in comparison to normal aging. The study of sleep variables and that of the spectral composition of the EEG can provide valuable information for understanding the pathophysiology and for assisting the diagnosis of neurodegenerative diseases.

Acetylcholine in mind: a neurotransmitter correlate of consciousness?

The cholinergic system is one of the most important modulatory neurotransmitter systems in the brain and controls activities that depend on selective attention, which are an essential component of conscious awareness. Psychopharmacological and pathological evidence supports the concept of a 'cholinergic component' of conscious awareness. Drugs that antagonize muscarinic receptors induce hallucinations and reduce the level of consciousness, while the nicotinic receptor is implicated as being involved in the mechanism of action of general (inhalational) anaesthetics. In degenerative diseases of the brain, alterations in consciousness are associated with regional deficits in the cholinergic system. In Alzheimer's disease (AD), there is a loss of explicit (more than implicit) memory and hypoactivity of cholinergic projections to the hippocampus and cortex, while the visual hallucinations experienced by subjects with Dementia with Lewy bodies (DLB) are associated with reductions in neocortical ACh-related activity. In Parkinson's disease, the additional loss of pedunculopontine cholinergic neurones, which control REM (rapid eye movement) sleep or dreaming, is likely to contribute to REM abnormalities, which also occur in DLB. Widespread basal-forebrain and rostral brainstem cholinergic pathways, which include converging projections to the thalamus, appear to be located strategically for generating and integrating conscious awareness. Alleviation of a range of cognitive and non-cognitive symptoms by drugs that modulate the cholinergic system, which are being developed for the treatment of AD and related disorders, could be caused by changes in consciousness.

Disorders of excessive daytime sleepiness--an update

Disorders of excessive daytime sleepiness (EDS) constitute a major health hazard, since impaired alertness may lead to accidents and poor quality of life, and some of them are associated with increased cardiovascular morbidity and mortality. Many disorders of EDS are neurological diseases (e.g. narcolepsy and periodic limb movements in sleep, PLMS). The largest group of disorders causing EDS consists of sleep-related disturbances of breathing, where neuroregulatory mechanisms play a major role in pathophysiology. Many patients with neurodegenerative and neuromuscular diseases suffer from sleep disturbances associated with EDS. Therefore, neurologists must be acquainted with the differential diagnosis of EDS and the major categories of sleep disorders causing it. The present update focuses on major sleep disorders causing EDS, and approaches the topic from the neurologist's perspective. Rather than being an extensive review, this update includes recent data on epidemiology, pathophysiology, diagnosis and treatment of obstructive sleep apnea and related conditions (increased upper airway resistance syndrome, central sleep apnea), as well as of narcolepsy and PLMS. Also included are recent data concerning EDS in neurodegenerative (Alzheimer's disease, Parkinson's disease, multiple system atrophy) and neuromuscular disorders.