There are many diseases that can cause dementia, and it is impossible to list them all here. We will mainly talk about the two main diseases that cause dementia, one is Alzheimer’s dementia, also known as Alzheimer’s dementia, and the other is vascular dementia, which is dementia caused by cerebrovascular disease. Alzheimer’s dementia was first described by the German physician Alzheimer in 1906 and is therefore named after him. Although Alzheimer’s disease has been studied extensively, the cause of the disease has not yet been clarified, except that in elderly patients, there is a large increase in the number of senile plaques and neurogenic fiber tangles in the brain, and nerve cells die, resulting in severe brain atrophy. Alzheimer’s disease is not uncommon, according to foreign statistics, 10% of the population over 60 years old will suffer from the disease, while those over 80 years old can be as much as 20% or more. In China, by the year 2000, the elderly population (the population over 60 years old) can reach about 130 million, so there are at least 13 million patients with Alzheimer’s disease, what a huge number! Vascular dementia is the consequence of multiple episodes of cerebrovascular disease. Cerebrovascular disease is mainly caused by hypertension and arteriosclerosis, the onset of which is very rapid, often with hemiplegia and unclear speech, and can gradually recover after treatment. Both Alzheimer’s and vascular dementia are associated with sleep disorders, characterized by disturbances in the sleep rhythm. These elderly patients have reversed day and night, they are drowsy during the day, whether they are lying or sitting, they can snore gently and go to sleep, but at night they have a steep increase in energy, refuse to sleep, run around and rummage through things, and sometimes shout and yell, which seriously affects the rest and sleep of others. The period of REM sleep is roughly similar to normal sleep. The EEG shows a slower rhythm, but it is not very different from that of a normal elderly person. The elderly with dementia should be careful not to use sleeping pills that are too intense, as they can cause excessive drowsiness and sometimes produce aspiration pneumonia, which can be life-threatening.