dementia
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What is dementia?
Dementia is a broad term for various conditions involving chronic and progressive decline in intellectual capacity, stemming from nerve cell loss and brain tissue shrinkage. Those affected experience impaired memory, learning, and diminished executive functions, impacting attention, language, and social skills.
Alzheimer's disease stands as the most prevalent irreversible form of dementia. Other types include Lewy body dementia, frontotemporal dementia, and vascular dementia, the second most common, resulting from a series of small strokes. Though there is no cure for dementia, treatments exist to slow its progression and alleviate symptoms. Preventative measures such as physical activity, a healthy diet, and avoiding smoking may also help.
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Which parts of the brain are affected by dementia?
Dementia is a condition characterized by a decline in intellectual capacity, impacting various brain regions. Alzheimer's disease, the most prevalent cause of dementia, affects the entire cerebral cortex, especially the frontal lobe, and is marked by atrophy in the hippocampal formation, leading to spatial orientation and navigation problems.
Vascular dementia, stemming from small strokes, impairs brain function, while other conditions such as Huntington's disease can cause thinning of the cerebral cortex. Treatable dementias can occur in hypothyroidism and metabolic diseases.
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What changes happen in brain cells during dementia?
In dementia, several changes occur in brain cells, varying based on the specific type of dementia. Common changes include the loss of neurons, reduced levels of neurotransmitters, and the presence of abnormal protein deposits.
In Alzheimer's disease, the most prevalent form of dementia, brain cells exhibit neuritic plaques (deposits of neuron fragments surrounding amyloid beta-protein) and neurofibrillary tangles (twisted fibers of tau protein within neurons). These plaques and tangles disrupt normal cell function, and are diagnostic hallmarks found upon autopsy.
In dementia with Lewy bodies, there is an abnormal accumulation of alpha-synuclein protein in various brain regions, as well as a reduction in activity in the brain's cholinergic system.
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How do these changes lead to memory loss?
Dementia, including Alzheimer's disease and dementia with Lewy bodies, is characterized by a decline in memory and cognitive abilities due to changes in the brain.
These changes include the destruction of nerve cells and neural connections, as well as a loss of brain mass. In dementia with Lewy bodies, an abnormal buildup of alpha-synuclein occurs in areas of the brain that are important for memory and learning. Alzheimer's disease is associated with diminished levels of neurotransmitters, which transmit signals between nerve cells, and with tissue lesions in the cerebral cortex. Atrophy in the hippocampal formation, a brain area involved in spatial memory, is also an early feature of Alzheimer's disease.
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What are some common causes of dementia in the brain?
Dementia is a condition marked by a decline in intellectual capacity, resulting from nerve cell loss and brain tissue shrinkage. The most common cause of irreversible dementia is Alzheimer's disease, which is associated with diminished levels of neurotransmitters and the development of neuritic plaques and neurofibrillary tangles in the cerebral cortex. Another major cause is vascular conditions, such as hypertension, leading to multi-infarct dementia from a series of small strokes. Other conditions, such as Parkinson's disease and dementia with Lewy bodies, are also associated with dementia. Additional causes may include Huntington's disease, multiple sclerosis, AIDS, and encephalitis.
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How is dementia diagnosed by examining the brain’s pathology?
Dementia diagnosis through brain pathology relies on identifying specific structural changes and abnormalities. Examination of the brain during autopsy can reveal key indicators such as:
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Neuritic plaques Also known as senile, dendritic, or amyloid plaques, these consist of deteriorating neuronal material surrounding deposits of amyloid-beta protein.
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Neurofibrillary tangles Twisted protein fibers composed of tau protein located within nerve cells.
The presence of these plaques and tangles, along with a loss of neurons, are characteristic of Alzheimer's disease, the most common form of dementia. The identification of these features aids in confirming the diagnosis and understanding the underlying pathology of dementia.
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dementia, general term for any of a number of conditions marked by chronic, usually progressive deterioration of intellectual capacity associated with the widespread loss of nerve cells and the shrinkage of brain tissue. People with dementia experience impairments in memory and learning, executive functioning, complex attention, language, perceptual-motor or visuospatial function, and social cognition. It is most commonly seen in the elderly (senile dementia), but dementia is not an inevitable part of the aging process and can affect persons of any age. In 2005 researchers reported that some 24.3 million people worldwide were living with dementia. In 2015 this figure rose to an estimated 47.5 million, a number that was expected to increase significantly by 2030, in part because of anticipated increases in life expectancy in many countries. In the 2013 revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM), there was a shift from the term dementia, and this group of disorders was categorized under “major neurocognitive disorder” in DSM-5. For a major neurocognitive disorder diagnosis, a patient must experience cognitive impairment that significantly interferes with everyday functioning. This impairment should be evident when compared with one’s previous levels of cognitive functioning. For less severe forms of cognitive impairment, DSM-5 uses a “mild neurocognitive disorder” diagnosis. The term dementia, however, continues to be in use in society and medical literature.
The most common irreversible dementia is Alzheimer disease. This condition often begins with memory loss or with subtle impairments in other cognitive functions. These changes may manifest initially as simple absentmindedness or forgetfulness or as minor problems with judgment, language, or perception. As the disease progresses, memory loss and cognitive impairment broaden in scope until the individual can no longer remember basic social and survival skills or function independently. Language, spatial or temporal orientation, judgment, perception, and other cognitive capacities decline, and personality changes may occur.
Dementia is also present in other degenerative brain diseases, including Pick disease and Parkinson disease. Another form of dementia, known as limbic-predominant age-related TDP-43 encephalopathy (LATE), closely resembles Alzheimer disease. Although LATE is also marked by the deterioration of memory and cognition and declines in social skills, patterns of neurocognitive change and the rate of decline in LATE differ from Alzheimer disease. Other major forms of dementia are dementia due to Lewy body disease, frontotemporal dementia, and dementia due to psychoactive substances.
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The second most common cause of dementia is hypertension (high blood pressure) or other vascular conditions. This type of dementia, called multi-infarct, or vascular, dementia, results from a series of small strokes that progressively destroy the brain. Dementia can also be caused by Huntington disease, syphilis, multiple sclerosis, acquired immune deficiency syndrome (AIDS), and some types of encephalitis. Treatable dementias occur in hypothyroidism, other metabolic diseases, and some malignant tumors. Treatment of underlying disease may inhibit the progress of dementia but usually does not reverse it.
Because many instances of dementia are not necessarily a consequence of aging but rather are associated with lifestyle factors, certain behaviors can help delay or potentially prevent dementia. Guidelines for dementia prevention issued by the World Health Organization include engaging in physical activity, never smoking, limiting alcohol intake, eating a healthy diet, and managing weight. Particularly in persons age 55 or older, risk of dementia may be increased by the use of certain prescription drugs, especially anticholinergic agents, which are used to treat a variety of conditions, including allergies, bladder disorders, chronic obstructive pulmonary disease (COPD), and depression.