Dementia is a mental health disorder caused by injury or changes in the brain. There are many causes of dementia – some can be reversed with treatment but most cannot be. Dementia affects memory and other mental skills (thinking and behaviour), that have an affect on a person’s daily life. In most cases the symptoms worsen as the disease progresses and can become severe enough to interfere with daily tasks. The rate of progress can vary – some people may stay the same for years whereas others may have rapid decline of mental functions. Most people with dementia may live for months, years or decades, depending on the cause of the disease and associated medical conditions.
Expected duration of treatable causes of dementia
There are some treatable causes of dementia such as underactive thyroid gland (hypothyroidism), vitamin B12 deficiency, lead poisoning, infection, certain brain tumours and chronic alcoholism. If dementia is caused by a treatable condition, treatment of the underlying disorder can reverse dementia. For example, early diagnosis and treatment of dementia caused by vitamin deficiency can lead to full recovery of memory.
Expected duration of dementia that cannot be reversed with treatment
In people with vascular dementia caused by stroke, memory loss can remain stable for years if there is no further damage to brain (because of interruption of blood supply). Further damage to brain can be prevented by taking medicines to control risk factors such as high blood pressure and diabetes. These drugs do not reverse existing damage to brain and dementia, but lower the risk of future strokes and heart disease that can aggravate damage to brain.
Decline of mental functions (memory, thinking, behaviour) in Alzheimer's disease usually progresses slowly over eight to 15 year (can range from two to 25 years). Currently, there is no cure for Alzheimer's disease (AD) but treatments can help to alleviate many of the symptoms, and may delay progression of the disease. Death in AD patients usually occurs due to problems like difficulty in swallowing or walking which can lead to overwhelming infections, such as pneumonia, and other complications.
As in Alzheimer's disease, the decline of mental functions (memory, thinking, behaviour) occurs at a variable rate in most other types of dementia (such as fronto-temporal dementia, dementia with Lewy bodies) which cannot be treated. In some people the decline may be rapid and in others, slow. Medications do not cure dementia but may help to improve mental functions, mood or behaviour. The condition progresses at a variable rate over the years until the person's death. Depending on the cause, the person's age, general health and the availability of treatments, life expectancy can vary from a few months or as long as 15 to 20 years.