Dementia refers to a category of diseases that cause loss of memory and deterioration in other mental functions. Dementia occurs due to physical changes in the brain and is a progressive disease, meaning it gets worse over time. For some people, dementia progresses rapidly, while it takes years to reach an advanced stage for others. The progression of dementia depends greatly on the underlying cause of the dementia. While people will experience the stages of dementia differently, most people with dementia share some of the symptoms.

The symptoms and progression of the disease depend on the type of dementia a person has. Some of the most commonly diagnosed forms of dementia are:

Alzheimer’s disease

Alzheimer’s disease is the most common form of dementia. It accounts for 60 to 80 percent of cases. It’s usually a slowly progressing disease. The average person lives four to eight years after receiving the diagnosis. Some people may live as many as 20 years after their diagnosis.

Alzheimer’s occurs due to physical changes in the brain, including a buildup of certain proteins and nerve damage.

Dementia with Lewy bodies

Dementia with Lewy bodies is a form of dementia that occurs due to clumps of a protein in the cortex. In addition to memory loss and confusion, dementia with Lewy bodies can also cause:

Vascular dementia

Vascular dementia, also known as post-stroke or multi-infarct dementia, accounts for about 10 percent of all cases of dementia. It’s caused by blocked blood vessels. These occur in strokes and other brain injuries.

Parkinson’s disease

Parkinson’s disease is a neurodegenerative condition that can produce dementia similar to Alzheimer’s in its later stages. The disease more commonly leads to problems with movement and motor control, but it also can cause dementia in some people.

Frontotemporal dementia

Frontotemporal dementia refers to a group of dementias that often cause changes in personality and behavior. It can also cause language difficulty. Frontotemporal dementia can occur due to a range of conditions, including Pick’s disease and progressive supranuclear palsy.

Mixed dementia

Mixed dementia is dementia in which multiple types of dementia-causing brain abnormalities are present. This is most commonly Alzheimer’s and vascular dementia, but it can include other forms of dementia as well.