Alzheimer Disease in Older Adults

Alzheimer disease is the most common cause of dementia in older adults. It is a progressive neurodegenerative disorder characterised pathologically by amyloid-beta plaques and tau neurofibrillary tangles, and clinically, in its typical late-onset form, by an insidious decline that usually begins with episodic memory and extends to other cognitive domains and daily function.

Definition

Alzheimer disease is a progressive neurodegenerative disorder defined by amyloid-beta plaque and tau neurofibrillary tangle pathology, presenting in its common late-onset form as a gradually progressive amnestic dementia that eventually impairs multiple cognitive domains and the capacity for independent living.

Scope

This topic covers the typical clinical presentation of late-onset Alzheimer disease, its underlying pathology, the continuum from preclinical disease through MCI to dementia, and the diagnostic frameworks used to recognise it. It is a reference entry and does not provide diagnostic protocols, dosing, or treatment recommendations.

Core questions

• What is the typical clinical course of late-onset Alzheimer disease?
• How do amyloid-beta and tau pathology relate to the clinical syndrome?
• How is Alzheimer disease situated on the continuum from preclinical disease to dementia?
• How is dementia due to Alzheimer's disease distinguished from other dementias?

Key concepts

• Amyloid-beta plaques
• Tau neurofibrillary tangles
• Insidious, progressive amnestic presentation
• Preclinical, MCI, and dementia stages
• Late-onset versus early-onset disease
• Biomarker-supported diagnosis

Key theories

Amyloid cascade hypothesis

A long-influential framework proposing that accumulation of amyloid-beta is an early, upstream event in Alzheimer pathogenesis that contributes to downstream tau pathology, neuronal injury, and cognitive decline; it remains a central organising idea even as its completeness and therapeutic implications are debated.

Mechanisms

Alzheimer disease is marked by extracellular amyloid-beta plaques and intracellular tau neurofibrillary tangles, accompanied by synaptic loss and neurodegeneration that typically begins in medial temporal structures and spreads through association cortex. This anatomical progression parallels the clinical picture, in which early episodic memory impairment is followed by deficits in language, executive function, and visuospatial ability. The amyloid cascade hypothesis frames amyloid accumulation as an early upstream event, though the relationship between pathology and symptoms is complex and continues to be studied.

Clinical relevance

Understanding the typical course and pathology of Alzheimer disease helps clinicians and learners interpret cognitive complaints in older adults and situate them within a recognised disease continuum. This entry is educational; it characterises the disease rather than providing individualised diagnostic or therapeutic guidance.

Epidemiology

Alzheimer disease is the leading cause of dementia and its prevalence rises markedly with age, making it a dominant contributor to the global dementia burden documented in sources such as the Alzheimer's Association facts and figures reports. In older brains it frequently coexists with vascular and other pathologies.

Evidence & guidelines

Recognition of Alzheimer disease is framed by the National Institute on Aging-Alzheimer's Association recommendations spanning preclinical disease, MCI, and dementia, together with comprehensive reviews such as Scheltens et al. (2016). These are referenced for orientation, not as care instructions.

History

Alois Alzheimer's early-twentieth-century description of a patient with progressive dementia and characteristic plaques and tangles gave the disease its name. Diagnostic criteria evolved over the late twentieth century, and the 2011 National Institute on Aging-Alzheimer's Association revisions reconceived the disease as a continuum extending from a preclinical biomarker-defined stage through MCI to dementia.

Debates

How central is amyloid to the disease?

The amyloid cascade hypothesis has organised much research, but the degree to which amyloid drives clinical decline, and how this should translate into intervention, remains actively debated within the field.

Key figures

• Philip Scheltens
• Guy McKhann
• Marilyn Albert

Seminal works

• mckhann-2011
• scheltens-2016

Frequently asked questions

What is usually the earliest symptom of late-onset Alzheimer disease?

In the typical late-onset form, the earliest prominent symptom is usually impairment of episodic memory, such as difficulty recalling recent events or conversations, with other cognitive domains affected as the disease progresses.

Is Alzheimer disease the same as dementia?

No. Dementia is a syndrome of acquired cognitive impairment severe enough to affect daily function, and Alzheimer disease is the most common underlying cause of that syndrome, but not the only one.