Progression of mild cognitive impairment to Alzheimer's disease: improved diagnostic value of the combined use of N200 latency and beta-amyloid(1-42) levels

CSF Biomarkers in the Early Diagnosis of Mild Cognitive Impairment and Alzheimer's Disease

Alzheimer's disease (AD) is a rapidly growing disease that affects millions of people worldwide, therefore there is an urgent need for its early diagnosis and treatment. A huge amount of research studies are performed on possible accurate and reliable diagnostic biomarkers of AD. Due to its direct contact with extracellular space of the brain, cerebrospinal fluid (CSF) is the most useful biological fluid reflecting molecular events in the brain. Proteins and molecules that reflect the pathogenesis of the disease, e.g., neurodegeneration, accumulation of Abeta, hyperphosphorylation of tau protein and apoptosis may be used as biomarkers. The aim of the current manuscript is to present the most commonly used CSF biomarkers for AD as well as novel biomarkers. Three CSF biomarkers, namely total tau, phospho-tau and Abeta42, are believed to have the highest diagnostic accuracy for early AD diagnosis and the ability to predict AD development in mild cognitive impairment (MCI) patients. Moreover, other biomarkers such as soluble amyloid precursor protein (APP), apoptotic proteins, secretases and inflammatory and oxidation markers are believed to have increased future prospects.

How far is the goal of applying β-amyloid in cerebrospinal fluid for clinical diagnosis of Alzheimer's disease with standardization of measurements?

Cerebrospinal fluid (CSF) β-amyloid (Aβ) is important for early diagnosis of Alzheimer's disease (AD). However, the cohort distributions and cut-off values have large variation across different analytical assays, kits, and laboratories. In this review, we summarize the cut-off values and diagnostic performance for CSF Aβ1-42 and Aβ1-42/Aβ1-40, and explore the important effect factors. Based on the Alzheimer's Association external quality control program (AAQC program), the peer group coefficient of variation of manual ELISA assays for CSF Aβ1-42 was unsatisfied (>20%). Fully automated platforms with better performance have recently been developed, but still not widely applied. In 2020, the certified reference material (CRM) for CSF Aβ1-42 was launched; however, the AAQC 2021-round results did not show effective improvements. Thus, further development and popularization of CRM for CSF Aβ1-42 and Aβ1-40 are urgently required. Standardizing the diagnostic procedures of AD and related status and the pre-analytical protocols of CSF samples, improving detection performance of analytical assays, and popularizing the application of fully automated platforms are also important for the establishment of uniform cut-off values. Moreover, each laboratory should verify the applicability of uniform cut-off values, and evaluate whether it is necessary to establish its own population- and assay-specific cut-off values.

A Systematic Review and Meta-Analysis of Cerebrospinal Fluid Amyloid and Tau Levels Identifies Mild Cognitive Impairment Patients Progressing to Alzheimer's Disease

Reported levels of amyloid-beta and tau in human cerebrospinal fluid (CSF) were evaluated to discover if these biochemical markers can predict the transition from Mild Cognitive Impairment (MCI) to Alzheimer’s disease (AD). A systematic review of the literature in PubMed and Web of Science (April 2021) was performed by a single researcher to identify studies reporting immunologically-based (xMAP or ELISA) measures of CSF analytes Aβ(1-42) and/or P-tau and/or T-tau in clinical studies with at least two timepoints and a statement of diagnostic criteria. Of 1137 screened publications, 22 met the inclusion criteria for CSF Aβ(1-42) measures, 20 studies included T-tau, and 17 included P-tau. Six meta-analyses were conducted to compare the analytes for healthy controls (HC) versus progressive MCI (MCI_AD) and for non-progressive MCI (Stable_MCI) versus MCI_AD; effect sizes were determined using random effects models. The heterogeneity of effect sizes across studies was confirmed with very high significance (p < 0.0001) for all meta-analyses except HC versus MCI_AD T-tau (p < 0.05) and P-tau (non-significant). Standard mean difference (SMD) was highly significant (p < 0.0001) for all comparisons (Stable_MCI versus MCI_AD: SMD [95%-CI] Aβ(1-42) = 1.19 [0.96,1.42]; T-tau = −1.03 [−1.24,−0.82]; P-tau = −1.03 [−1.47,−0.59]; HC versus MCI_AD: SMD Aβ(1-42) = 1.73 [1.39,2.07]; T-tau = −1.13 [−1.33,−0.93]; P-tau = −1.10 [−1.23,−0.96]). The follow-up interval in longitudinal evaluations was a critical factor in clinical study design, and the Aβ(1−42)/P-tau ratio most robustly differentiated progressive from non-progressive MCI. The value of amyloid-beta and tau as markers of patient outcome are supported by these findings.

Treatment effects on event-related EEG potentials and oscillations in Alzheimer's disease

Alzheimer's disease dementia (ADD) is the most diffuse neurodegenerative disorder belonging to mild cognitive impairment (MCI) and dementia in old persons. This disease is provoked by an abnormal accumulation of amyloid-beta and tauopathy proteins in the brain. Very recently, the first disease-modifying drug has been licensed with reserve (i.e., Aducanumab). Therefore, there is a need to identify and use biomarkers probing the neurophysiological underpinnings of human cognitive functions to test the clinical efficacy of that drug. In this regard, event-related electroencephalographic potentials (ERPs) and oscillations (EROs) are promising candidates. Here, an Expert Panel from the Electrophysiology Professional Interest Area of the Alzheimer's Association and Global Brain Consortium reviewed the field literature on the effects of the most used symptomatic drug against ADD (i.e., Acetylcholinesterase inhibitors) on ERPs and EROs in ADD patients with MCI and dementia at the group level. The most convincing results were found in ADD patients. In those patients, Acetylcholinesterase inhibitors partially normalized ERP P300 peak latency and amplitude in oddball paradigms using visual stimuli. In these same paradigms, those drugs partially normalize ERO phase-locking at the theta band (4-7 Hz) and spectral coherence between electrode pairs at the gamma (around 40 Hz) band. These results are of great interest and may motivate multicentric, double-blind, randomized, and placebo-controlled clinical trials in MCI and ADD patients for final cross-validation.

Memory Clinics and Day Care Centers in Thessaloniki, Northern Greece: 30 Years of Clinical Practice and Experience

Background: This review describes the diagnostic and interventional procedures conducted in two university memory clinics (established network of G. Papanikolaou Hospital: 1988–2017 and AHEPA hospital: 2017–today) and 2 day care centers (established network of DCCs: 2005–today) in North Greece and their contribution in the scientific field of dementia. The aims of this work are (1) to provide a diagnosis and treatment protocol established in the network of memory clinics and DCCs and (2) to present further research conducted in the aforementioned network during the last 30 years of clinical practice.

Methods: The guidelines to set a protocol demand a series of actions as follows: (1) set the diagnosis criteria, neuropsychological assessment, laboratory examinations, and examination of neurophysiological, neuroimaging, cerebrospinal fluid, blood, and genetic markers; and (2) apply non-pharmacological interventions according to the needs and specialized psychosocial interventions of the patient to the caregivers of the patient.

Results: In addition to the guidelines followed in memory clinics at the 1st and 3rd Department of Neurology and two DCCs, a database of patients, educational programs, and further participation in international research programs, including clinical trials, make our contribution in the dementia field strong.

Conclusion: In the current paper, we provide useful guidelines on how major and minor neurocognitive disorders are being treated in Thessaloniki, Greece, describing successful practices which have been adapted in the last 30 years.

Cortical auditory evoked potentials in mild cognitive impairment: Evidence from a temporal-spatial principal component analysis

Mild cognitive impairment (MCI) is considered an intermediate transitional stage for the development of dementia, especially Alzheimer's disease. The identification of neurophysiological biomarkers for MCI will allow improvement in detecting and tracking the progression of cognitive impairment. The primary objective of this study was to compare cortical auditory evoked potentials between older adults with and without probable MCI to identify potential neurophysiological indicators of cognitive impairment. We applied a temporal-spatial principal component analysis to the evoked potentials achieved during the processing of pure tones and speech sounds, to facilitate the separation of the components of the P1-N1-P2 complex. The probable MCI group showed a significant amplitude increase in a factor modeling N1b for speech sounds (Cohen's d = .84) and a decrease in a factor around the P2 time interval, especially for pure tones (Cohen's d = 1.17). Moreover, both factors showed a fair discrimination value between groups (area under the curve [AUC] = .698 for N1b in speech condition; AUC = .746 for P2 in tone condition), with high sensitivity to detect MCI cases (86% and 91%, respectively). The results for N1b suggest that MCI participants may suffer from a deficit to inhibit irrelevant speech information, and the decrease of P2 amplitude could be a signal of cholinergic hypoactivation. Therefore, both components could be proposed as early biomarkers of cognitive impairment.

Sino Longitudinal Study on Cognitive Decline (SILCODE): protocol for a Chinese longitudinal observational study to develop risk prediction models of conversion to mild cognitive impairment in individuals with subjective cognitive decline

INTRODUCTION

Understanding the biological mechanism of subjective cognitive decline (SCD) in preclinical Alzheimer's disease (AD) and identifying those who will soon convert to mild cognitive impairment (MCI) are critical for developing appropriate strategies for early diagnosis and intervention of AD. We present the study protocol of the Sino Longitudinal Study on Cognitive Decline (SILCODE), a longitudinal observational study focusing on SCD in the context of AD.

METHODS AND ANALYSIS

Within SILCODE, approximately 800 subjects with SCD who are between 50 and 79 years old will be recruited through standardised public advertisements or memory clinics. They will undergo extensive assessment, including clinical and neuropsychological assessments, blood sample collection for plasma beta-amyloid and ApoE genotype, urine samples collection for AD7c-NTP, and multimodal MRI scans (structural MRI, diffusion tensor imaging, resting-state functional MRI and optional task-based functional MRI) as well as optional glucose metabolism and amyloid positron emission tomography. Subjects will be contacted by telephone every 3 months and interviewed, on average, every 15 months for 5 years. The study endpoint is the development of mild cognitive impairment or dementia. Jak & Bondi's actuarial neuropsychological method will be used for diagnosis of MCI. The least absolute shrinkage and selection operator logistic regression model followed by the sub-distribution hazard function model with death as a competing risk will be constructed to establish risk prediction models.

ETHICS AND DISSEMINATION

The ethics committee of the Xuanwu Hospital of Capital Medical University has approved this study protocol (ID: [2017]046). The results will be published in peer-reviewed journals and presented at national and international scientific conferences.

TRIAL REGISTRATION NUMBER

NCT03370744; Pre-results.

Abnormal auditory mismatch fields are associated with communication impairment in both verbal and minimally verbal/nonverbal children who have autism spectrum disorder

Abnormal auditory discrimination neural processes, indexed by mismatch fields (MMFs) recorded by magnetoencephalography (MEG), have been reported in verbal children with ASD. Association with clinical measures indicates that delayed MMF components are associated with poorer language and communication performance. At present, little is known about neural correlates of language and communication skills in extremely language impaired (minimally-verbal/non-verbal) children who have ASD: ASD-MVNV. It is hypothesized that MMF delays observed in language-impaired but nonetheless verbal children with ASD will be exacerbated in ASD-MVNV. The present study investigated this hypothesis, examining MMF responses bilaterally during an auditory oddball paradigm with vowel stimuli in ASD-MVNV, in a verbal ASD cohort without cognitive impairment and in typically developing (TD) children. The verbal ASD cohort without cognitive impairment was split into those demonstrating considerable language impairment (CELF core language index <85; "ASD-LI") versus those with less or no language impairment (CELF CLI >85; "ASD-V"). Eighty-four participants (8-12 years) were included in final analysis: ASD-MVNV: n = 9, 9.67 ± 1.41 years, ASD: n = 48, (ASD-V: n = 27, 10.55 ± 1.21 years, ASD-LI: n = 21, 10.67 ± 1.20 years) and TD: n = 27, 10.14 ± 1.38 years. Delayed MMF latencies were found bilaterally in ASD-MVNV compared to verbal ASD (both ASD-V and ASD-LI) and TD children. Delayed MMF responses were associated with diminished language and communication skills. Furthermore, whereas the TD children showed leftward lateralization of MMF amplitude, ASD-MVNV and verbal ASD (ASD-V and ASD-LI) showed abnormal rightward lateralization. Findings suggest delayed auditory discrimination processes and abnormal rightward laterality as objective markers of language/communication skills in both verbal and MVNV children who have ASD. Autism Res 2019, 12: 1225-1235. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Brain imaging showed abnormal auditory discrimination processes in minimally-verbal/non-verbal children (MVNV) who have autism spectrum disorder (ASD). Delays in auditory discrimination were associated with impaired language and communication skills. Findings suggest these auditory neural measures may be objective markers of language and communication skills in both verbal and, previously-understudied, MVNV children who have ASD.

Can a Novel High-Density EEG Approach Disentangle the Differences of Visual Event Related Potential (N170), Elicited by Negative Facial Stimuli, in People with Subjective Cognitive Impairment?

BACKGROUND

Studies on subjective cognitive impairment (SCI) and neural activation report controversial results.

OBJECTIVE

To evaluate the ability to disentangle the differences of visual N170 ERP, generated by facial stimuli (Anger & Fear) as well as the cognitive deterioration of SCI, mild cognitive impairment (MCI), and Alzheimer's disease (AD) compared to healthy controls (HC).

METHOD

57 people took part in this study. Images corresponding to facial stimuli of "Anger" and "Fear" were presented to 12 HC, 14 SCI, 17 MCI and 14 AD participants. EEG data were recorded by using a HD-EEG HydroCel with 256 channels.

RESULTS

Results showed that the amplitude of N170 can contribute in distinguishing the SCI group, since statistically significant differences were observed with the HC (p < 0.05) and the MCI group from HC (p < 0.001), as well as AD from HC (p = 0.05) during the processing of facial stimuli. Noticeable differences were also observed in the topographic distribution of the N170 amplitude, while localization analysis by using sLORETA images confirmed the activation of superior, middle-temporal, and frontal lobe brain regions. Finally, in the case of "Fear", SCI and HC demonstrated increased activation in the orbital and inferior frontal gyrus, respectively, MCI in the inferior temporal gyrus, and AD in the lingual gyrus.

CONCLUSION

These preliminary findings suggest that the amplitude of N170 elicited after negative facial stimuli could be modulated by the decline related to pathological cognitive aging and can contribute in distinguishing HC from SCI, MCI, and AD.

Auditory system dysfunction in Alzheimer disease and its prodromal states: A review

Recent findings suggest that both peripheral and central auditory system dysfunction occur in the prodromal stages of Alzheimer Disease (AD), and therefore may represent early indicators of the disease. In addition, loss of auditory function itself leads to communication difficulties, social isolation and poor quality of life for both patients with AD and their caregivers. Developing a greater understanding of auditory dysfunction in early AD may shed light on the mechanisms of disease progression and carry diagnostic and therapeutic importance. Herein, we review the literature on hearing abilities in AD and its prodromal stages investigated through methods such as pure-tone audiometry, dichotic listening tasks, and evoked response potentials. We propose that screening for peripheral and central auditory dysfunction in at-risk populations is a low-cost and effective means to identify early AD pathology and provides an entry point for therapeutic interventions that enhance the quality of life of AD patients.

Increased N200 and P300 latencies in cognitively impaired elderly carrying ApoE ε-4 allele

OBJECTIVE

To compare the results of neuropsychological tests, evoked potentials N200 and P300 and polymorphisms of ApoE and BDNF rs6265 between patients with normal cognition and those with mild cognitive impairment (MCI) and Alzheimer's dementia (AD).

METHODS

This is a cross-sectional study of elderly individuals with normal cognition and those with MCI and AD, who were submitted to evoked potential tests (N200 and P300) by means of hearing stimuli based on the auditory oddball paradigm. Genotyping was obtained by using the real-time PCR technique.

RESULTS

Sixty-five patients were evaluated as follows: 14 controls, 34 with MCI and 17 with AD. N200 latency and P300 latency and amplitude were not associated with MCI and AD diagnosis. Patients with cognitive impairment (MCI or AD) showed increase in the latencies of P300 and N200. BNDF gene was not associated with cognitive impairment.

CONCLUSION

Latencies of N200 and P300 increased in cognitively impaired patients with the presence of ApoE ε-4 allele.

Mismatch negativity latency as a biomarker of amnestic mild cognitive impairment in chinese rural elders

The aim was to evaluate the mismatch negativity (MMN) component, a correlate of the automatic detection of changes in the acoustic environment, in healthy adults, and adults with amnestic mild cognitive impairment (aMCI). Forty-three aMCI subjects and 43 healthy Chinese older adults were arranged into experimental group and control group, respectively. Their MMN amplitude and latency were measured at the FZ, FCZ, and CZ electrode sites under a passive auditory oddball task. The results showed that the latencies obtained from the FZ, FCZ, and CZ electrode sites were significantly longer in the aMCI adults than in the control adults (P  < 0.01) while there were no significant differences in MMN amplitude between two groups (P  > 0.05). The MMN latency was found to be a sensitive and specific biomarker of aMCI.

Using event-related potential P300 as an electrophysiological marker for differential diagnosis and to predict the progression of mild cognitive impairment: a meta-analysis

P300 event-related potential component may sensitively predict mild cognitive impairment (MCI) progression. Here, pooled effect size estimates of P300 amplitude and latency were computed at midline electrodes among controls, MCI patients, and Alzheimer's disease (AD) patients. Baseline data were compared to one-year follow-up data. MCI patients showed decreased P300 amplitude and prolonged latency compared to controls. Pooled standardized mean differences (SMDs) were -0.67 (95 % CI -1.12 to -0.23, P = 0.003) and 0.90 (95 % CI 0.66-1.14, P < 0.00001), respectively. P300 latency decreased in MCI compared to AD patients where the pooled SMD was -0.52 (95 % CI -0.85 to -0.18, P = 0.003). Amplitude and latency differed between MCI baseline and follow-up. Pooled SMDs were 0.47 (95 % CI 0.29 to -0.65, P < 0.00001) and -0.52 (95 % CI -0.71 to -0.34, P < 0.00001), respectively. Group differences in MCI P300 latency existed compared to control and AD patients. P300 latency may therefore be a sensitive indicator for early cognitive decline or disease progression in MCI patients and identifying elderly patient progression to MCI and/or AD.

Clinical workout for the early detection of cognitive decline and dementia

Aging is the major risk factor for the development of human neurodegenerative maladies such as Alzheimer's, Huntington's and Parkinson's diseases (PDs) and prion disorders, all of which stem from toxic protein aggregation. All of these diseases are correlated with cognitive decline. Cognitive Decline is a dynamic state from normal cognition of aging to dementia. According to the original criteria for Alzheimer's Disease (AD) (1984), a clinical diagnosis was possible only when someone was already demented. The prevalence rates of Cognitive Decline (mild cognitive impairment plus dementia) are very high now and will be higher in future because of the increasing survival time of people. Many neurological and psychiatric diseases are correlated with cognitive decline. Diagnosis of cognitive decline is mostly clinical (clinical criteria), but there are multiple biomarkers that could help us mostly in research programs such as short or long, paper and pencil or computerized neuropsychological batteries for cognition, activities of daily living and behavior, electroencephalograph, event-related potentials, and imaging-structural magnetic resonance imaging (MRI) and functional (fMRI, Pittsburgh bound positron emission tomography, FDG-PET, single photon emission computerized tomography and imaging of tau pathology)-cerebrospinal fluid proteins (Abeta, tau and phospho-tau in AD and α-synuclein (αSyn) for PD). Blood biomarkers need more studies to confirm their usefulness. Genetic markers are also studied but until now are not used in clinical praxis. Finally, in everyday clinical praxis and in research workout for early detection of cognitive decline, the combination of biomarkers is useful.

Plasma and cerebrospinal fluid amyloid beta for the diagnosis of Alzheimer's disease dementia and other dementias in people with mild cognitive impairment (MCI)

BACKGROUND

According to the latest revised National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (now known as the Alzheimer's Association) (NINCDS-ADRDA) diagnostic criteria for Alzheimer's disease dementia of the National Institute on Aging and Alzheimer Association, the confidence in diagnosing mild cognitive impairment (MCI) due to Alzheimer's disease dementia is raised with the application of biomarkers based on measures in the cerebrospinal fluid (CSF) or imaging. These tests, added to core clinical criteria, might increase the sensitivity or specificity of a testing strategy. However, the accuracy of biomarkers in the diagnosis of Alzheimer's disease dementia and other dementias has not yet been systematically evaluated. A formal systematic evaluation of sensitivity, specificity, and other properties of plasma and CSF amyloid beta (Aß) biomarkers was performed.

OBJECTIVES

To determine the accuracy of plasma and CSF Aß levels for detecting those patients with MCI who would convert to Alzheimer's disease dementia or other forms of dementia over time.

SEARCH METHODS

The most recent search for this review was performed on 3 December 2012. We searched MEDLINE (OvidSP), EMBASE (OvidSP), BIOSIS Previews (ISI Web of Knowledge), Web of Science and Conference Proceedings (ISI Web of Knowledge), PsycINFO (OvidSP), and LILACS (BIREME). We also requested a search of the Cochrane Register of Diagnostic Test Accuracy Studies (managed by the Cochrane Renal Group).No language or date restrictions were applied to the electronic searches and methodological filters were not used so as to maximise sensitivity.

SELECTION CRITERIA

We selected those studies that had prospectively well defined cohorts with any accepted definition of cognitive decline, but no dementia, with baseline CSF or plasma Aß levels, or both, documented at or around the time the above diagnoses were made. We also included studies which looked at data from those cohorts retrospectively, and which contained sufficient data to construct two by two tables expressing plasma and CSF Aß biomarker results by disease status. Moreover, studies were only selected if they applied a reference standard for Alzheimer's dementia diagnosis, for example the NINCDS-ADRDA or Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria.

DATA COLLECTION AND ANALYSIS

We screened all titles generated by the electronic database searches. Two review authors independently assessed the abstracts of all potentially relevant studies. We assessed the identified full papers for eligibility and extracted data to create standard two by two tables. Two independent assessors performed quality assessment using the QUADAS-2 tool. Where data allowed, we derived estimates of sensitivity at fixed values of specificity from the model we fitted to produce the summary receiver operating characteristic (ROC) curve.

MAIN RESULTS

Alzheimer's disease dementia was evaluated in 14 studies using CSF Aß42. Of the 1349 participants included in the meta-analysis, 436 developed Alzheimer's dementia. Individual study estimates of sensitivity were between 36% and 100% while the specificities were between 29% and 91%. Because of the variation in assay thresholds, we did not estimate summary sensitivity and specificity. However, we derived estimates of sensitivity at fixed values of specificity from the model we fitted to produce the summary ROC curve. At the median specificity of 64%, the sensitivity was 81% (95% CI 72 to 87). This equated to a positive likelihood ratio (LR+) of 2.22 (95% CI 2.00 to 2.47) and a negative likelihood ratio (LR-) of 0.31 (95% CI 0.21 to 0.48).The accuracy of CSF Aß42 for all forms of dementia was evaluated in four studies. Of the 464 participants examined, 188 developed a form of dementia (Alzheimer's disease and other forms of dementia).The thresholds used were between 209 mg/ml and 512 ng/ml. The sensitivities were between 56% and 75% while the specificities were between 47% and 76%. At the median specificity of 75%, the sensitivity was estimated to be 63% (95% CI 22 to 91) from the meta-analytic model. This equated to a LR+ of 2.51 (95% CI 1.30 to 4.86) and a LR- of 0.50 (95% CI 0.16 to 1.51).The accuracy of CSF Aß42 for non-Alzheimer's disease dementia was evaluated in three studies. Of the 385 participants examined, 61 developed non-Alzheimer's disease dementia. Since there were very few studies and considerable variation between studies, the results were not meta-analysed. The sensitivities were between 8% and 63% while the specificities were between 35% and 67%.Only one study examined the accuracy of plasma Aß42 and the plasma Aß42/Aß40 ratio for Alzheimer's disease dementia. The sensitivity of 86% (95% CI 81 to 90) was the same for both tests while the specificities were 50% (95% CI 44 to 55) and 70% (95% CI 64 to 75) for plasma Aß42 and the plasma Aß42/Aß40 ratio respectively. Of the 565 participants examined, 245 developed Alzheimer's dementia and 87 non-Alzheimer's disease dementia.There was substantial heterogeneity between studies. The accuracy of Aß42 for the diagnosis of Alzheimer's disease dementia did not differ significantly (P = 0.8) between studies that pre-specified the threshold for determining test positivity (n = 6) and those that only determined the threshold at follow-up (n = 8). One study excluded a sample of MCI non-Alzheimer's disease dementia converters from their analysis. In sensitivity analyses, the exclusion of this study had no impact on our findings. The exclusion of eight studies (950 patients) that were considered at high (n = 3) or unclear (n = 5) risk of bias for the patient selection domain also made no difference to our findings.

AUTHORS' CONCLUSIONS

The proposed diagnostic criteria for prodromal dementia and MCI due to Alzheimer's disease, although still being debated, would be fulfilled where there is both core clinical and cognitive criteria and a single biomarker abnormality. From our review, the measure of abnormally low CSF Aß levels has very little diagnostic benefit with likelihood ratios suggesting only marginal clinical utility. The quality of reports was also poor, and thresholds and length of follow-up were inconsistent. We conclude that when applied to a population of patients with MCI, CSF Aß levels cannot be recommended as an accurate test for Alzheimer's disease.

Mismatch negativity (MMN) amplitude as a biomarker of sensory memory deficit in amnestic mild cognitive impairment

It has been suggested that changes in some event-related potential (ERP) parameters associated with controlled processing of stimuli could be used as biomarkers of amnestic mild cognitive impairment (aMCI). However, data regarding the suitability of ERP components associated with automatic and involuntary processing of stimuli for this purpose are not conclusive. In the present study, we studied the Mismatch Negativity (MMN) component, a correlate of the automatic detection of changes in the acoustic environment, in healthy adults and adults with aMCI (age range: 50-87 years). An auditory-visual attention-distraction task, in two evaluations separated by an interval of between 18 and 24 months, was used. In both evaluations, the MMN amplitude was significantly smaller in the aMCI adults than in the control adults. In the first evaluation, such differences were observed for the subgroup of adults between 50 and 64 years of age, but not for the subgroup of 65 years and over. In the aMCI adults, the MMN amplitude was significantly smaller in the second evaluation than in the first evaluation, but no significant changes were observed in the control adult group. The MMN amplitude was found to be a sensitive and specific biomarker of aMCI, in both the first and second evaluation.

Event-related potentials for the diagnosis of mild cognitive impairment and Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) and the nosological entity of mild cognitive impairment (MCI) constitute a major public health concern. The diagnostic approach and therapeutic management of these disorders may be significantly improved by recent advances in the field of event-related potentials (ERPs).

AREAS COVERED

The authors performed a PubMed search in order to identify full-length, original research articles on the experimental and clinical application of ERPs in AD and MCI. The major part of the retrieved articles concerns the application of auditory and, to a lesser extent, visual ERPs for the early diagnosis of AD and MCI. Particular emphasis was placed on the role of ERPs in identifying the subgroup of MCI patients who will subsequently convert to AD. Other areas covered include the contribution of ERPs in the differential diagnosis of dementia types, the utility of ERPs for monitoring pharmacological treatment in AD and the correlation between ERPs and the results of neuropsychological testing.

EXPERT OPINION

The reviewed evidence suggests that ERPs hold promise as an electrophysiological tool for the early and accurate diagnosis of AD and MCI. However, certain methodological issues need to be resolved before ERPs enter the arena of clinical practice.

Biomarkers in Alzheimer's disease drug development

Developing new therapies for Alzheimer's disease (AD) is critically important to avoid the impending public health disaster imposed by this common disorder. Means must be found to prevent, delay the onset, or slow the progression of AD. These goals will be achieved by identifying disease-modifying therapies and testing them in clinical trials. Biomarkers play an increasingly important role in AD drug development. In preclinical testing, they assist in decisions to develop an agent. Biomarkers in phase I provide insights into toxic responses and drug metabolism and in Phase II proof-of-concept trials they facilitate go/no-go decisions and dose finding. Biomarkers can play a role in identifying presymptomatic patients or specific patient subgroups. They can provide evidence of target engagement before clinical changes can be expected. Brain imaging can serve as a primary outcome in Phase II trials and as a key secondary outcome in Phase III trials. Magnetic resonance imaging is currently best positioned for use in large multicenter clinical trials. Cerebrospinal fluid (CSF) measures of amyloid beta protein (Aβ), tau protein, and hyperphosphorylated tau (p-tau) protein are sensitive and specific to the diagnosis of AD and may serve as inclusion criteria and possibly as outcomes in clinical trials targeting relevant pathways. Plasma measures of Aβ are of limited diagnostic value but may provide important information as a measure of treatment response. A wide variety of measures of detectable products of cellular processes are being developed as possible biomarkers accessible in the cerebrospinal fluid and plasma or serum. Surrogate markers that can function as outcomes in pivotal trials and reliably predict clinical outcomes are needed to facilitate primary prevention trials of asymptomatic persons where clinical measures may be of limited value. Fit-for-purpose biomarkers are increasingly available to guide AD drug development decisions.