Medically Reviewed by Smitha Bhandari, MD on February 08, 2023
5 min read



Dementia is a broad term that describes a loss of thinking ability, memory, attention, logical reasoning, and other mental abilities. These changes are severe enough to interfere with social or occupational functioning.

Many things can cause dementia. It happens when the parts of your brain used for learning, memory, decision making, and language are damaged or diseased.

You might also hear it called major neurocognitive disorder. Dementia isn’t a disease. Instead, it's a group of symptoms caused by other conditions.

About 5%-8% of adults over age 65 have some form of dementia. This percentage doubles every 5 years after 65. As many as half of people in their 80s have some dementia.

Alzheimer's disease is the most common cause of dementia. Between 60%-80% of people with dementia have Alzheimer's. But there are as many as 50 other causes of dementia.

Dementia symptoms may improve with treatment. But many of the diseases that cause dementia aren't curable.

These forms of dementia are partially manageable, but they aren't reversible:

  • Alzheimer's disease
  • Vascular dementia
  • Dementia from Parkinson's disease and similar disorders
  • Dementia with Lewy bodies
  • Frontotemporal dementia (Pick's disease)
  • Creutzfeldt-Jakob disease

Dementia can be split into two groups based on which part of the brain is affected.

Cortical dementias happen because of problems in the cerebral cortex, the outer layer of the brain. They play a critical role in memory and language. People with these types of dementia usually have severe memory loss and can't remember words or understand language. Alzheimer's and Creutzfeldt-Jakob disease are two forms of cortical dementia.

Subcortical dementias happen because of problems in the parts of the brain beneath the cortex. People with subcortical dementias tend to show changes in their speed of thinking and ability to start activities. Usually, people with subcortical dementia don't have forgetfulness and language problems. Parkinson's disease, Huntington's disease, and HIV can cause these types of dementia.

Some types of dementia affect both parts of the brain. For example, Lewy Body dementia is both cortical and subcortical.

Dementia is not temporary confusion or forgetfulness that might result from an infection that heals without treatment. It can also come from an underlying illness or side effects of medications. Dementia typically gets worse over time.

The most common causes of dementia include:

Degenerative neurological diseases. These include:

  • Alzheimer's disease
  • Parkinson's disease
  • Huntington's disease
  • Some types of multiple sclerosis.

These diseases get worse over time.

Vascular disorders. These conditions affect the blood circulation in your brain.

  • Traumatic brain injuries caused by car accidents, falls, concussions, etc.
  • Infections of the central nervous system. These include meningitis, HIV, and Creutzfeldt-Jakob disease.
  • Long-time alcohol or drug use
  • Certain types of hydrocephalus, a buildup of fluid in the brain

Some reversible causes of dementia include:

  • Alcohol or substance use disorder
  • Tumors
  • Subdural hematomas, blood clots beneath the outer covering of the brain
  • Normal-pressure hydrocephalus, a buildup of fluid in the brain
  • Metabolic disorders such as a vitamin B12 deficiency
  • Low levels of thyroid hormones, called hypothyroidism
  • Low blood sugar, called hypoglycemia
  • HIV-associated neurocognitive disorders (HAND)

Certain physical and lifestyle factors can raise your chances of dementia,  including:

  • Age
  • Dementia in your family
  • Illnesses including diabetes, Down syndrome, multiple sclerosis, heart disease, and sleep apnea
  • Depression
  • Smoking, heavy alcohol use, poor diet, and lack of exercise
  • Brain injury
  • Strokes
  • Infection of the brain (for example, meningitis and syphilis)

People with dementia have problems with thinking and remembering that affect their ability to manage their daily life.

These are some signs to watch for:

  • Short-term memory problems, like forgetting where you put something or asking the same question over and over
  • Communication problems like not being able to come up with a word
  • Getting lost
  • Trouble with complex but familiar tasks, like fixing a meal or paying bills
  • Personality changes, like depression, agitation, paranoia, and mood swings

Usually, dementia goes through these stages. But it may vary depending on the area of the brain that’s affected.

1. No impairment. Someone at this stage will show no symptoms, but tests may reveal a problem.

2. Very mild decline. You may notice slight changes in behavior, but your loved one will still be independent.

3. Mild decline. You'll notice more changes in their thinking and reasoning. They may have trouble making plans, and they may repeat themselves a lot. They may also have a hard time remembering recent events.

4. Moderate decline. They'll have more problems with making plans and remembering recent events. They may have a hard time with traveling and handling money.

5. Moderately severe decline. They may not remember their phone number or their grandchildren's names. They may be confused about the time of day or day of the week. At this point, they’ll need assistance with some basic day-to-day functions, such as picking out clothes to wear.

6. Severe decline. They'll begin to forget the name of their spouse. They’ll need help going to the restroom and eating. You may also see changes in their personality and emotions.

7. Very severe decline. They can no longer speak their thoughts. They can't walk and will spend most of their time in bed.

The doctor will review the patient's history and perform a physical exam and cognitive testing. Further testing might happen depending on the history and physical.

This testing might include:

  • Blood and urine tests
  • Chest X-ray
  • Brain scanning (MRI or CT scanning)
  • Electroencephalogram (EEG)
  • Spinal fluid analysis

They use certain criteria to diagnose dementia. These include:

  • impairment of attention
  • Orientation
  • Memory
  • Judgment
  • Language, motor, and spatial skills and function. (By definition, dementia is not due to major depression or schizophrenia.)

To treat dementia, doctors will treat whatever is causing it. About 20% of the causes of dementia are reversible. If the cause of a person’s dementia is not reversible, treatment will focus on managing symptoms, particularly agitation and other emotional concerns.

Aducanumab-avwa (Aduhelm) and lecanemab-irmb (Leqembi are two drugs approved by the FDA to treat Alzheimer's disease. If your loved one is in the early stages of Alzheimer's disease, the most common form of dementia, their doctor may prescribe either of these as an infusion therapy. Aduhelm is taken monthly while Leqembi is every two weeks. Both are monoclonal antibodies that lessen the buildup of things called amyloid plaques in your brain. These plaques are part of what leads to the memory loss associated with Alzheimer's disease.

Medicines such as acetylcholinesterase inhibitors (for example, donepezil and galantamine) can sometimes help to slow the progression of cognitive changes, but quite often the effects of medicines are only modest and cannot prevent the eventual worsening of the underlying condition.