Dementia is a progressively deteriorating condition that affects brain functions such as memory, thinking, and cognition to such an extent that it interferes with routine daily activities. The early symptoms of dementia are mild such as simple episodes of forgetfulness and confusion. As the disease progresses, it causes frequent forgetfulness events, more confusion, poor decision-making ability, and repetitive questioning. In severe cases, the person with dementia may have difficulty remembering names or addresses, fail to recognize family members and be incapable of maintaining.
Dementia is a slowly progressive disorder in which a decline in brain function is divided into seven stages according to the severity of memory and thinking dysfunction. The staging based on the Global Deterioration scale acts as an assessment tool for recognizing brain damage (1) .
Alzheimer's disease is the most common cause of dementia, making up 60-70 percent of dementia in older adults (2) .
Other types include:
In some cases, Alzheimer's disease and vascular dementia have been found to coexist, called mixed dementia.
In the following sections, we will discuss the similarities and differences among three common types of dementia, i.e., Alzheimer's disease, Vascular dementia and Lewy body dementia.
The widely accepted hypothesis for the causation of Alzheimer's is the abnormal aggregation of amyloid beta and neurofibrillary tangles in the brain. This leads to the loss of connections between brain cells resulting in the dysfunction and death of brain cells. However, there has been a growing concern regarding the amyloid hypothesis, as clinical trial results on drugs that reduce amyloid beta aggregates in the brain have failed to show an improvement in the symptoms (3) .
Vascular dementia is typically caused by a stroke where the blood supply to the critical areas of the brain is interrupted. It results in loss of oxygen and nutrition supply to brain cells causing neuronal death. As the brain is highly vulnerable to hypoxia, cell death occurs suddenly after a stroke.
Similar to Alzheimer's, Lewy body dementia is caused by the unusual accumulation of the alpha-synuclein protein, also known as Lewy body in the brain. This deposition of proteins interferes with the electrical signals between brain cells.
Alzheimer's disease involves different regions of the brain in a specific pattern. In the initial stages, loss of neuronal connections occurs in the hippocampus and entorhinal cortex, which results in memory loss. It then progresses to other cortical regions leading to a decline in cognitive functions such as problem-solving, decision-making and language impairments. In contrast, Vascular dementia is heterogeneous as it depends on the location and size of the brain region that is affected by the interruption of blood supply during a stroke (4) . In Lewy Body Dementia, the accumulation of Lewy bodies leads to the deficiency of acetylcholine and dopamine neurotransmitters in different areas of the brain, such as the cerebral cortex and the limbic system (5) .
All three types of dementia overlap and have common symptoms such as memory loss, thinking difficulties and cognitive decline. However, certain differences can help to distinguish among them. Alzheimer's disease is characterized by memory problems at an early stage and deterioration of language, reasoning, and behavioral skills at the later stages. However, in Lewy body dementia, thinking disorders and visual hallucinations are prominent symptoms in the early stages. As the disease progresses, it causes a decline in memory, thinking and cognition along with symptoms of Parkinson's disease such as muscle rigidity, tremors, difficulty with speech, swallowing and initiating movements (6) . Vascular dementia, the decline does not occur in a specific pattern; symptoms vary depending on the location and size of the brain region that had the blood flow cut off during a stroke. A major stroke may cause impairment in memory, thinking, concentrating, and planning. However, a minor stroke in the hippocampus region may cause memory loss and impaired learning skills. Later on, as the damage extends to a greater region of the brain, the symptoms may become similar to Alzheimer’s disease-causing memory problems, confusion, and low mood.
Dementia is a general term used for declining memory and thinking. Alzheimer's disease is one of the most common causes of dementia, constituting 60-70 percent of dementia in older adults. It progresses slowly and causes a continuous decline in memory, thinking, and cognitive abilities. Vascular dementia can damage any brain region due to a stroke, whereas in Lewy body dementia, protein deposits are the main cause of neuronal dysfunction and cognitive deterioration.
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