There are several possible causes of dementia, some of which are reversible and others that are not. Many types of dementia tend to get worse with time. Alzheimer’s disease is the most common type, accounting for about 2/3 of dementia cases. Other types include vascular dementia, which is probably the next most common type, Lewy body dementia, and frontotemporal dementia. Still other cases can be caused by head trauma, other neurological diseases like multiple sclerosis and Parkinson’s disease, or infections like encephalitis or HIV/AIDS.
Alzheimer’s disease occurs when brain cells called neurons die in parts of the brain important for memory and conscious thought. The cause of this neural cell death is still being investigated but patients with the disease always have accumulations of dead or dying cells called plaques and tangles found around accumulations of certain abnormal brain proteins. Alzheimer’s disease is progressive and fatal and there is currently no cure.
Vascular dementia occurs when the blood vessels that feed the brain become narrowed or blocked. This causes strokes, which may be large and obvious or small and undetected. In either case, cells that are deprived of blood due to the strokes die and this leads to dementia. Some people have both Alzheimer’s disease and vascular dementia. It may be possible to prevent progression of vascular dementia by treating the underlying cause of the strokes, but there is no way to reverse the damage that has already been done.
Lewy body dementia is similar to Alzheimer’s disease in that clumps of dead or dying cells (called Lewy bodies) are found in the area of an abnormal brain protein, but the protein is different than those found in the plaques and tangles of Alzheimer’s. Frontotemporal dementia is a type of dementia that preferentially affects the frontal and temporal lobes of the brain and so affects personality and behavior. It is unknown why cells in these brain areas die but it tends to run in families and may also be related to accumulations of abnormal proteins.
Other causes of dementia include degenerative neurological diseases such as Huntington’s disease, Parkinson’s disease, and Creutzfeldt-Jakob disease. Many other conditions, some of them reversible, can cause dementia or dementia-like symptoms. These include: reactions to medication or interactions between more than one medication; nutritional or metabolic disorders such as hypothyroidism, hypoglycemia, deficiency of vitamins vitamin B-1, B-3, or B-12, and dehydration; and infections such as encephalitis and meningitis.