The National Institute on Aging and the Alzheimer's Association charged a workgroup with the task of revising the 1984 criteria for Alzheimer's disease (AD) dementia. The workgroup sought to ensure that the revised criteria would be flexible enough to be used by both general healthcare providers without access to neuropsychological testing, advanced imaging, and cerebrospinal fluid measures, and specialized investigators involved in research or in clinical trial studies who would have these tools available. We present criteria for all-cause dementia and for AD dementia. We retained the general framework of probable AD dementia from the 1984 criteria. On the basis of the past 27 years of experience, we made several changes in the clinical criteria for the diagnosis. We also retained the term possible AD dementia, but redefined it in a manner more focused than before. Biomarker evidence was also integrated into the diagnostic formulations for probable and possible AD dementia for use in research settings. The core clinical criteria for AD dementia will continue to be the cornerstone of the diagnosis in clinical practice, but biomarker evidence is expected to enhance the pathophysiological specificity of the diagnosis of AD dementia. Much work lies ahead for validating the biomarker diagnosis of AD dementia.

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The diagnosis of dementia due to Alzheimer’s disease: Recommendations from the National Institute on Aging-Alzheimer’s Association workgroups on diagnostic guidelines for Alzheimer's disease

The pathophysiological process of Alzheimer's disease (AD) is thought to begin many years before the diagnosis of AD dementia. This long "preclinical" phase of AD would provide a critical opportunity for therapeutic intervention; however, we need to further elucidate the link between the pathological cascade of AD and the emergence of clinical symptoms. The National Institute on Aging and the Alzheimer's Association convened an international workgroup to review the biomarker, epidemiological, and neuropsychological evidence, and to develop recommendations to determine the factors which best predict the risk of progression from "normal" cognition to mild cognitive impairment and AD dementia. We propose a conceptual framework and operational research criteria, based on the prevailing scientific evidence to date, to test and refine these models with longitudinal clinical research studies. These recommendations are solely intended for research purposes and do not have any clinical implications at this time. It is hoped that these recommendations will provide a common rubric to advance the study of preclinical AD, and ultimately, aid the field in moving toward earlier intervention at a stage of AD when some disease-modifying therapies may be most efficacious.

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Toward defining the preclinical stages of Alzheimer's disease: Recommendations from the National Institute on Aging-Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease

In 2011, the National Institute on Aging and Alzheimer's Association created separate diagnostic recommendations for the preclinical, mild cognitive impairment, and dementia stages of Alzheimer's disease. Scientific progress in the interim led to an initiative by the National Institute on Aging and Alzheimer's Association to update and unify the 2011 guidelines. This unifying update is labeled a "research framework" because its intended use is for observational and interventional research, not routine clinical care. In the National Institute on Aging and Alzheimer's Association Research Framework, Alzheimer's disease (AD) is defined by its underlying pathologic processes that can be documented by postmortem examination or in vivo by biomarkers. The diagnosis is not based on the clinical consequences of the disease (i.e., symptoms/signs) in this research framework, which shifts the definition of AD in living people from a syndromal to a biological construct. The research framework focuses on the diagnosis of AD with biomarkers in living persons. Biomarkers are grouped into those of β amyloid deposition, pathologic tau, and neurodegeneration [AT(N)]. This ATN classification system groups different biomarkers (imaging and biofluids) by the pathologic process each measures. The AT(N) system is flexible in that new biomarkers can be added to the three existing AT(N) groups, and new biomarker groups beyond AT(N) can be added when they become available. We focus on AD as a continuum, and cognitive staging may be accomplished using continuous measures. However, we also outline two different categorical cognitive schemes for staging the severity of cognitive impairment: a scheme using three traditional syndromal categories and a six-stage numeric scheme. It is important to stress that this framework seeks to create a common language with which investigators can generate and test hypotheses about the interactions among different pathologic processes (denoted by biomarkers) and cognitive symptoms. We appreciate the concern that this biomarker-based research framework has the potential to be misused. Therefore, we emphasize, first, it is premature and inappropriate to use this research framework in general medical practice. Second, this research framework should not be used to restrict alternative approaches to hypothesis testing that do not use biomarkers. There will be situations where biomarkers are not available or requiring them would be counterproductive to the specific research goals (discussed in more detail later in the document). Thus, biomarker-based research should not be considered a template for all research into age-related cognitive impairment and dementia; rather, it should be applied when it is fit for the purpose of the specific research goals of a study. Importantly, this framework should be examined in diverse populations. Although it is possible that β-amyloid plaques and neurofibrillary tau deposits are not causal in AD pathogenesis, it is these abnormal protein deposits that define AD as a unique neurodegenerative disease among different disorders that can lead to dementia. We envision that defining AD as a biological construct will enable a more accurate characterization and understanding of the sequence of events that lead to cognitive impairment that is associated with AD, as well as the multifactorial etiology of dementia. This approach also will enable a more precise approach to interventional trials where specific pathways can be targeted in the disease process and in the appropriate people.

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NIA-AA Research Framework: Toward a biological definition of Alzheimer's disease

1. Introduction and Overview. 2. Detecting Influential Observations and Outliers. 3. Detecting and Assessing Collinearity. 4. Applications and Remedies. 5. Research Issues and Directions for Extensions. Bibliography. Author Index. Subject Index.

Regression Diagnostics: Identifying Influential Data and Sources of Collinearity

2016 Alzheimer's disease facts and figures

The Integrated Alzheimer's Disease (AD) Rating Scale (iADRS) is a composite tool that combines scores from the AD Assessment Scale-Cognitive subscale (ADAS-Cog) and the AD Cooperative Study - instrumental Activities of Daily Living (ADCS-iADL). It demonstrates acceptable psychometric properties, and is effective in capturing both disease progression and separation of placebo and active drug effect. We assessed the performance of iADRS in the solanezumab EXPEDITION3 study, an 80-week, placebo-controlled study of individuals with mild AD dementia. A statistically significant difference between placebo and active drug was observed for iADRS score change from baseline at Week 28 (p=0.028) through Week 80 (p=0.015). Across the Phase 3 solanezumab trials, iADRS was the only tool that consistently differentiated between solanezumab and placebo groups. These findings suggest that the iADRS is a useful integrated measurement tool for treatment trials of individuals with mild AD dementia.

The Integrated Alzheimer's Disease Rating Scale (iADRS) Findings from the EXPEDITION3 Trial.

The A4 trial: Anti-amyloid treatment of asymptomatic Alzheimer's disease

The number of clinical trials for Alzheimer's disease conducted outside the United States in a broad array of countries is increasing. As the number of compounds ready for clinical testing increases, and as trials become longer and more complex, this trend is expected to grow. The cultural and ethical context of global clinical trials, potential benefits for those involved, and practical approaches to obstacles generated by these global trials were discussed at a meeting of the Alzheimer's Association Research Roundtable. Regulatory issues, including regional differences in study registration procedures, rules for collecting and reporting serious adverse events, requirements for national identity of study populations, and regulatory audits were also discussed by individuals who are knowledgeable about global clinical trials for Alzheimer's disease.

Global issues in drug development for Alzheimer's disease

Incidence and clinical progression of placebo-treated amyloid-negative subjects with mild-to-moderate Alzheimer's disease (AD): Results from the phase III PET substudies of bapineuzumab and solanezumab

Alzheimer's disease (AD) clinical trials are designed and powered to detect the impact of a therapeutic intervention, and there has been considerable discussion on what constitutes a clinically meaningful change in those receiving treatment versus placebo. The pathology of AD is complex, beginning many years before clinical symptoms are detectable, with multiple potential opportunities for therapeutic engagement. Introducing treatment strategies early in the disease and assessing meaningful change over the course of an 18‐month clinical trial are critical to understanding the value to an effective intervention. With new clinical trial data expected soon on emerging therapeutics from several AD studies, the Alzheimer's Association convened a work group of experts to discuss key considerations for interpreting data from cognitive and functional measures and what is considered a clinically meaningful benefit or meaningful slowing of this fatal disease. Our expectations of outcomes from therapeutic interventions in AD may need to be modified.

Eric Siemers

Papers

The Integrated Alzheimer's Disease Rating Scale (iADRS) Findings from the EXPEDITION3 Trial.

The A4 trial: Anti-amyloid treatment of asymptomatic Alzheimer's disease

Global issues in drug development for Alzheimer's disease

Incidence and clinical progression of placebo-treated amyloid-negative subjects with mild-to-moderate Alzheimer's disease (AD): Results from the phase III PET substudies of bapineuzumab and solanezumab

Expectations and clinical meaningfulness of randomized controlled trials