TABLE 1.
Common causes of dementia.*
| Cause | Brain changes | Percentage of dementia cases | Symptoms |
|---|---|---|---|
| Alzheimer's disease | Accumulation of the protein beta amyloid outside neurons and twisted strands of the protein tau inside neurons are hallmarks. They are accompanied by the death of neurons and damage to brain tissue. Inflammation and atrophy of brain tissue are other changes. | Alzheimer's is the most common cause of dementia, accounting for an estimated 60% to 80% of cases. Most individuals also have the brain changes of one or more other causes of dementia. 21 , 22 This is called mixed pathologies and if recognized during life is called mixed dementia. | Difficulty remembering recent conversations, names or events; apathy; and depression are often early symptoms. Communication problems, confusion, poor judgment and behavioral changes may occur next. Difficulty walking, speaking and swallowing are common in the late stages the disease. |
| Cerebrovascular disease | Blood vessels in the brain are damaged and/or bran tissue is injured from not receiving enough blood, oxygen or nutrients. People with these changes who develop dementia symptoms are said to have vascular dementia. | About 5% to 10% of individuals with dementia show evidence of vascular dementia alone. 21 , 22 However, it is more common as a mixed pathology with most people showing the brain changes of cerebrovascular disease and Alzheimer's disease. 21 , 22 | Slowed thoughts or impaired ability to make decisions, plan or organize may be the initial symptoms, but memory may also be affected. People with vascular dementia may become less emotional and have difficulty with motor function, especially slow gait and poor balance. |
| Frontotemporal degeneration (FTD) | Nerve cells in the front and temporal (side) lobes of the brain die and the lobes shrink. Upper layers of the cortex soften. Abnormal amounts or forms of tau or transactive response DNA‐binding protein (TDP‐43) are present. | About 60% of people with FTD are ages 45 to 60. 23 In a systematic review, FTD accounted for about 3% of dementia cases in studies that included people 65 and older and about 10% of dementia cases in studies restricted to those younger than 65. 24 | Typical early symptoms include marked changes in personality and behavior and/or difficulty with producing or comprehending language. Unlike Alzheimer's, memory is typically spared in the early stages of disease. |
| Hippocampal sclerosis (HP) | HS is the shrinkage and hardening of tissue in the hippocampus of the brain. The hippocampus plays a key role informing memories. HS brain changes are often accompanied by accumulation of the misfolded protein TDP‐43. | HS is present in about 3% to 13% of people with dementia. 25 It often occurs with the brain changes of other causes of dementia. An estimated 0.4% to 2% of dementia cases are due to HS alone. 25 | The most pronounced symptom of HS is memory loss, and individuals are often misdiagnosed as having Alzheimer's disease. HS is a common cause of dementia in individuals age 85 or older. |
| Lewy body disease | Lewy bodies are abnormal aggregations (or clumps) of the protein alpha‐synuclein in neurons. When they develop in a part of the brain called the cortex, dementia can result. This is called dementia with Lewy bodies or DLB. | About 5% of older individuals with dementia show evidence of DLB alone, but most people with DLB also have the brain changes of Alzheimer's disease. 26 | Early symptoms include sleep disturbances, well‐formed visual hallucinations and visuospatial impairment. These symptoms may change dramatically throughout the day or from day to day. Problems with motor function (similar to Parkinson's disease) are common. Memory loss may occur at some point in the disease. |
| Mixed pathologies | When an individual shows the brain changes of more than one cause of dementia, "mixed pathologies" are considered the cause. When these pathologies result in dementia symptoms during life, the person is said to have mixed dementia or mixed etiology dementia. | More than 50% of people diagnosed with Alzheimer's dementia who were studied at Alzheimer's Disease Research Centers had mixed dementia. 22 In community‐based studies, the percentage is considerably higher. 21 Mixed dementia is most common in people age 85 or older. 27 , 28 | Symptoms vary depending on the combination of brain changes present. |
| Parkinson's disease (PD) | Clumps of the protein alpha‐synuclein appear in an area deep in the brain called the substantia nigra. These clumps are thought to cause degeneration of the nerve cells that produce the chemical dopamine. 29 As PD progresses, alpha‐synuclein can also accumulate in the cortex. | A systematic review found that 3.6% of dementia cases were due to PD and 24.5% of people with PD developed dementia. 30 | Problems with movement (slowness, rigidity, tremor and changes in gait) are common symptoms of PD. Cognitive symptoms may develop later in the disease, typically years after movement symptoms. |
*
This table describes the most common causes of dementia. Emerging causes such as limbic predominant age related TDP‐43 encephalopathy (LATE) are under active investigation.