Alzymer disease
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"Alzheimer disease"[MeSH Terms] AND treatment
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I now have comprehensive information from Harrison's Principles of Internal Medicine 22E (2025) and Kaplan & Sadock's Psychiatry to build a thorough answer. Let me compile everything.
Alzheimer's Disease
Overview
Alzheimer's disease (AD) is the most common cause of dementia, accounting for an estimated 60-70% of all dementia cases worldwide. Approximately 55 million people globally live with dementia. U.S. health care costs related to dementia care were estimated at $360 billion in 2024 (~$25,000 per patient). Prevalence rises sharply with age: 3% at age 65-74, and 32% in those 85 and older. The lifetime risk from age 45 is ~10% for men and ~20% for women.
- Harrison's Principles of Internal Medicine 22E, 2025
- Bradley and Daroff's Neurology in Clinical Practice
Historical Background
AD was first described in 1906 by Alois Alzheimer, a German psychiatrist, who reported a woman in her 50s with paranoia, memory loss, aphasia, and eventual motor loss. At autopsy, he found an atrophic brain with microscopic inclusions now known as amyloid plaques and neurofibrillary tangles (NFTs).
Pathology and Pathophysiology
The hallmarks of AD at a microscopic level:
- Neuritic plaques - containing amyloid beta (Aβ) peptide
- Neurofibrillary tangles (NFTs) - composed of hyperphosphorylated tau filaments
- Aβ accumulation in blood vessel walls (cerebral amyloid angiopathy)
Brain atrophy in typical amnestic AD begins in the medial temporal lobes (hippocampus, entorhinal cortex) before spreading to inferior temporal, lateral and medial parietal, and dorsolateral frontal cortices.
The Amyloid Cascade
Aβ plaques are formed by abnormal processing of amyloid precursor protein (APP). The two leading pathogenic theories both center on Aβ and tau proteins. Mutations in APP, PSEN1 (presenilin-1), and PSEN2 (presenilin-2) cause rare autosomal dominant early-onset AD (less than 1% of cases).
Cholinergic Hypothesis
Early subcortical changes occur in the nucleus basalis of Meynert, which provides cholinergic innervation to the hippocampus and cortex. Decline of acetylcholine in these areas is strongly linked to cognitive impairment - this is the basis for cholinergic (acetylcholinesterase inhibitor) therapy.
- Kaplan & Sadock's Comprehensive Textbook of Psychiatry
Genetics and Risk Factors
| Factor | Details |
|---|---|
| ApoE ε4 | Major genetic risk factor; 1 allele = 2-3x risk (women); 2 alleles = 10-15x risk (both sexes) |
| Age | Strongest risk factor - incidence: 2/1000 (age 65-74), 37/1000 (age 85+) |
| Sex | Women have higher lifetime prevalence (longer lifespan) |
| APP mutation | Rare autosomal dominant, early onset |
| PSEN1/PSEN2 | Rare autosomal dominant, early onset |
| BuChE K variant + ApoE4 | Combined increased risk |
Clinical Stages and Features
Early Stage (Mild)
- Insidious episodic memory loss (most common presentation)
- Word-finding difficulty and circumlocution
- Subjective cognitive decline, then Mild Cognitive Impairment (MCI)
- ~50% of MCI patients progress to dementia over 4 years (~12% per year)
- Depression, social withdrawal, and anxiety may precede cognitive symptoms
- Preclinical biomarker changes can begin 20 or more years before symptoms
Middle Stage (Moderate)
- Unable to work, easily lost, requires daily supervision
- Language impairment: first naming, then comprehension, then fluency
- Apraxia (trouble with learned motor tasks - using utensils, appliances)
- Visuospatial deficits (dressing, eating, walking)
- Fails simple puzzles, geometric figures; difficulty with calculations and clock reading
Late Stage (Severe)
- Wandering, severe loss of judgment
- Delusions (theft, infidelity, misidentification)
- Disinhibition, agitation, alternating with passivity
- Sleep-wake disruption, nighttime wandering
- Shuffling gait, muscle rigidity, parkinsonian features possible
- Eventually rigid, mute, incontinent, bedridden
Typical disease duration: 8-10 years (range: 1-25 years)
Death most commonly results from aspiration pneumonia, secondary infections, pulmonary emboli, or heart disease.
- Harrison's Principles of Internal Medicine 22E
Diagnosis
A diagnosis of probable AD requires:
- Objective evidence of decline in memory and at least one other cognitive domain
- Insidious onset and gradual progression
- No evidence of another etiology
- DSM-5 terminology: "Major neurocognitive disorder due to Alzheimer disease"
Definitive diagnosis still requires postmortem neuropathological examination showing plaques and NFTs in hippocampal and entorhinal regions.
Biomarker Framework (AT(N))
The NIA-AA Research Framework uses three biomarker groupings:
- A = Amyloid (low CSF Aβ42 or amyloid PET positive)
- T = Tau (elevated CSF phospho-tau or tau PET positive)
- (N) = Neurodegeneration (atrophy on MRI, hypometabolism on FDG-PET)
Amyloid and tau PET imaging are now FDA-approved diagnostic tools. Updated appropriate use criteria for amyloid and tau PET were published by the Alzheimer's Association in 2025.
Imaging
- MRI/CT: Posteriorly predominant cortical and hippocampal atrophy
- Amyloid PET: Radiotracer retention in neocortex
- FDG-PET: Hypometabolism in temporoparietal regions
- Tau PET: Distribution correlates with clinical stage
A clinical diagnosis confirmed by careful workup is verified at autopsy ~70-80% of the time; misdiagnoses most often involve LATE (limbic-predominant age-related TDP-43 encephalopathy), Lewy body disease, or vascular pathology.
Treatment
Symptomatic Pharmacotherapy
| Drug | Class | Dose | Indication |
|---|---|---|---|
| Donepezil | AChE inhibitor | 10 mg/day | Mild-severe AD |
| Rivastigmine | AChE + BuChE inhibitor | 6 mg BID or 9.5 mg patch/day | Mild-severe AD |
| Galantamine | AChE inhibitor + nicotinic modulator | 24 mg/day (ER) | Mild-moderate AD |
| Memantine | NMDA antagonist | 10 mg BID | Moderate-severe AD |
- Cholinesterase inhibitors work by slowing breakdown of acetylcholine; the average patient maintains their MMSE score for ~1 year vs. 2-3 point decline in placebo
- Memantine blocks overexcited NMDA glutamate receptors and reduces agitation and caregiver burden in moderate-to-severe AD
- Common approach: start a cholinesterase inhibitor for mild AD; add memantine at the moderate stage
Disease-Modifying Therapies (Anti-Amyloid Antibodies)
A major therapeutic advance - these drugs promote clearance of amyloid plaques and represent the first class of disease-modifying therapies for AD:
| Drug | Target | Administration |
|---|---|---|
| Lecanemab | Aβ protofibrils | IV infusion every 2 weeks |
| Donanemab | Pyroglutamate-Aβ in plaques | IV infusion monthly |
Both are FDA-approved for early-stage AD (MCI or mild dementia) with biomarker confirmation of Aβ pathology. Phase 3 randomized controlled trials showed slowed clinical decline. A third antibody, aducanumab, was removed from clinical use due to ambiguous efficacy evidence.
Key restriction: Antiamyloid therapy is limited to patients with MCI or mild dementia who have confirmed Aβ pathology by PET or CSF. Patients with moderate-to-severe dementia or non-AD pathology are excluded.
- Harrison's Principles of Internal Medicine 22E, 2025
Non-Pharmacological & Lifestyle
A 2025 meta-analysis on Mediterranean diet and cognitive decline found the Mediterranean diet is associated with reduced risk of cognitive impairment, dementia, and AD.
Modifiable risk factors to address include:
- Cardiovascular risk factors (hypertension, diabetes, obesity)
- Physical inactivity
- Social isolation
- Sleep disturbances
- Depression management
Summary Table
| Feature | Detail |
|---|---|
| Prevalence | 60-70% of all dementia; 5.7 million+ in the U.S. |
| Key pathology | Aβ plaques + tau NFTs + cholinergic neuron loss |
| Main risk factor | Age; ApoE ε4 allele |
| Symptom onset | Insidious memory loss, then broader cognitive decline |
| Disease duration | 8-10 years average |
| Symptomatic Rx | Donepezil, rivastigmine, galantamine, memantine |
| Disease-modifying Rx | Lecanemab, donanemab (early-stage only) |
| Diagnosis | Clinical + biomarkers (amyloid/tau PET or CSF) |
Recent evidence note: Updated appropriate use criteria for amyloid and tau PET (2025, PMID 39776249) and Mediterranean diet meta-analysis (2025, PMID 39797935) may supplement the textbook content above with current evidence.
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