3.26
Dementia is an acquired and progressive decline in cognitive functions that interferes with daily living and social independence.
It involves impairment of memory and at least one other area of cortical function, such as language, calculation, spatial orientation, decision-making, judgment, or abstract reasoning.
The most common types include Alzheimer disease and vascular dementia.
Alzheimer disease, the leading cause of dementia, involves two hallmark brain changes.
Beta-amyloid plaques are abnormal protein clumps that accumulate between nerve cells, disrupting cell-to-cell communication.
Tau tangles inside the brain cells consist of hyperphosphorylated tau protein that twists inside neurons, impairing nutrient transport and destabilizing the cell’s internal structure.
Together, these changes lead to a gradual loss of neurons, especially in the hippocampus, which is crucial for memory.
Vascular dementia results from ischemic injury to the brain caused by multiple strokes due to blocked vessels or chronic small vessel disease, leading to a stepwise decline in cognitive function.
Dementia is an acquired, progressive syndrome characterized by a decline in multiple cognitive domains severe enough to impair daily functioning and reduce independence. Although memory loss is a central feature, the diagnosis requires additional deficits involving language, executive function, visuospatial skills, judgment, calculation, or abstract reasoning. These cognitive impairments reflect underlying neurodegenerative or vascular processes that gradually disrupt neuronal networks essential for higher cortical function.
Alzheimer’s Disease
Alzheimer’s disease is the most common cause of dementia and is defined by two hallmark pathological features. Beta-amyloid plaques form when amyloid-β peptides aggregate extracellularly and accumulate between neurons, interfering with synaptic signaling and triggering local inflammatory responses. Neurofibrillary tangles, composed of hyperphosphorylated tau protein, develop intracellularly. When tau becomes excessively phosphorylated, it detaches from microtubules, destabilizing the cytoskeleton and impairing axonal transport. These combined processes lead to synaptic dysfunction and progressive neuronal loss. Degeneration begins prominently in the hippocampus and medial temporal lobes—regions essential for forming new memories—and later spreads to association cortices, contributing to worsening cognitive impairment.
Vascular Dementia
Vascular dementia arises from compromised cerebral perfusion and oxygenation. Ischemic injury may occur through large-vessel infarcts, multiple small-vessel lacunar strokes, or chronic microvascular disease. Each of these processes disrupts cortical and subcortical pathways necessary for cognition. The resulting deficits often appear stepwise, corresponding to successive vascular events, and may include impaired attention, slowed processing speed, and executive dysfunction.
Dementia frequently involves mixed pathology, with both neurodegenerative and vascular contributions. Early recognition of symptoms and underlying mechanisms is essential for appropriate management, risk factor modification, and supportive care planning.
Dementia is an acquired and progressive decline in cognitive functions that interferes with daily living and social independence.
It involves impairment of memory and at least one other area of cortical function, such as language, calculation, spatial orientation, decision-making, judgment, or abstract reasoning.
The most common types include Alzheimer disease and vascular dementia.
Alzheimer disease, the leading cause of dementia, involves two hallmark brain changes.
Beta-amyloid plaques are abnormal protein clumps that accumulate between nerve cells, disrupting cell-to-cell communication.
Tau tangles inside the brain cells consist of hyperphosphorylated tau protein that twists inside neurons, impairing nutrient transport and destabilizing the cell’s internal structure.
Together, these changes lead to a gradual loss of neurons, especially in the hippocampus, which is crucial for memory.
Vascular dementia results from ischemic injury to the brain caused by multiple strokes due to blocked vessels or chronic small vessel disease, leading to a stepwise decline in cognitive function.
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