Alzheimer Disease
A fatal neurodegenerative disease defined by amyloid plaques and tau tangles, causing progressive memory loss, cognitive decline, and eventual loss of independent function.
Emergency Management: Severe behavioral disturbances or psychosis posing a threat to self or others. Management involves behavioral de-escalation; low-dose atypical antipsychotics (e.g., Quetiapine 12.5 mg) are used strictly off-label with black box warning for increased mortality.
Alzheimer disease is a progressive neurodegenerative disorder characterized by the extracellular deposition of amyloid-beta plaques and intracellular neurofibrillary tangles of hyperphosphorylated tau protein. It primarily affects the cerebral cortex and hippocampus, leading to significant brain atrophy. The condition is the most common cause of dementia, resulting in severe cognitive decline and memory loss.
Detailed Overview
The pathophysiology involves the cleavage of amyloid precursor protein (APP) into neurotoxic amyloid-beta (Aβ42) peptides, which aggregate into plaques. Concurrently, hyperphosphorylation of the microtubule-associated tau protein causes neuronal cytoskeleton collapse, forming neurofibrillary tangles. This dual accumulation disrupts synaptic communication, notably depleting acetylcholine levels in the basal nucleus of Meynert. As the disease advances, patients experience progressive aphasia, apraxia, and agnosia. Clinically, it poses a profound burden, necessitating comprehensive multidisciplinary care and caregiver support.
Epidemiology & Demographics
Accounts for 60-80% of dementia cases. Incidence increases exponentially with age, affecting ~5% of individuals over 65 and up to 30% over 85. More common in females (approximately 2:1 ratio), largely attributed to longer life expectancy.
Etiological Mechanism
Sporadic forms account for >95% of cases, heavily influenced by the Apolipoprotein E epsilon 4 (APOE-ε4) allele. Early-onset familial Alzheimer disease (<5% of cases) is caused by autosomal dominant mutations in the APP gene on chromosome 21, Presenilin 1 (PSEN1) on chromosome 14, and Presenilin 2 (PSEN2) on chromosome 1.
Primary Causes
Primary causes are genetic mutations (APP, PSEN1, PSEN2) for early-onset and complex genetic/environmental interactions for late-onset.
Misfolding and aggregation of Aβ42 peptides into extracellular plaques trigger microglial activation and neuroinflammation. Intracellularly, hyperphosphorylated tau proteins dissociate from microtubules, self-assembling into paired helical filaments known as neurofibrillary tangles. This leads to profound loss of cholinergic neurons, particularly in the basal forebrain, and glutamatergic excitotoxicity.
Diagnostic Criteria & Guidelines
Clinical diagnosis based on NIA-AA criteria requires insidious onset and progressive cognitive decline. Definitive diagnosis traditionally required autopsy, but in vivo diagnosis is now supported by biomarkers: low Aβ42 and elevated phosphorylated tau (p-tau181) in CSF, or positive amyloid/tau PET scans.
Acetylcholinesterase inhibitors (AChEIs) are first-line for mild to moderate disease. Donepezil 5 mg PO daily, titrated to 10 mg after 4-6 weeks (max 23 mg/day for severe). Rivastigmine patch 4.6 mg/24h titrated to 9.5 mg/24h. Galantamine ER 8 mg PO daily titrated to 16-24 mg/day.
Second-Line & Adjunctive Therapy
NMDA receptor antagonists for moderate to severe disease. Memantine 5 mg PO daily, titrated weekly by 5 mg increments to 10 mg PO BID. Can be used as monotherapy or combined with AChEIs (e.g., Namzaric). Disease-modifying monoclonal antibodies (Lecanemab 10 mg/kg IV every 2 weeks) for early AD with confirmed amyloid pathology.
Surgical & Procedural Management
No surgical management indicated for primary Alzheimer pathology. Gastrostomy tubes (PEG) are generally NOT recommended in advanced dementia due to lack of survival benefit and risk of complications.
Patient Counseling & Advice
Counsel families on driving cessation when navigating becomes impaired. Discuss caregiver burnout and refer to local support groups and respite care resources.
Follow-Up & Monitoring Schedule
Reassess cognitive status every 6 months using tools like MMSE or MoCA. Monitor weight, nutritional status, and functional independence (ADLs/IADLs).
Preventive Strategies
Strict management of mid-life cardiovascular risk factors (BP < 130/80 mmHg). Continuous cognitive engagement and high educational attainment contribute to cognitive reserve.
Average life expectancy is 4 to 8 years following diagnosis, though some may live up to 20 years. Prognosis is uniformly fatal, typically concluding with infectious complications like pneumonia.