Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community


    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Brain & Nervous System Health Center

Font Size

Types of Dementia

What Is Dementia?

Dementia is the loss of mental functions, such as thinking, memory, and reasoning, that is severe enough to interfere with a person's daily life. Dementia is not a disease itself but rather a group of symptoms that may accompany certain diseases or conditions. Symptoms may involve changes in personality, mood, and behavior.

Dementia develops when the parts of the brain that are involved with learning, memory, decision-making, and language are affected by injury or disease. The most common cause of dementia is Alzheimer's disease, which is considered responsible for at least half of all cases of dementia. However, there are as many as 50 other known causes of dementia, but most of these causes are very rare.

Recommended Related to Brain & Nervous System

The Continuum of Rehabilitation for Persons with Traumatic Brain Injury

According to the Centers for Disease Control and Prevention, a traumatic brain injury (TBI) occurs when an impact to the head results in disruption of brain functioning. While post-TBI physical impairments can hinder functional independence, the behavioral, cognitive, emotional, psychosocial, and personality changes associated with TBI frequently lead to even greater problems. Comprehensive evaluation and treatment are the foundation to optimizing outcome after TBI, as the complex functions affected,...

Read the The Continuum of Rehabilitation for Persons with Traumatic Brain Injury article > >

Although many diseases that cause dementia are not curable, some forms of dementia may improve greatly when the underlying cause is treated. For instance, if dementia is caused by vitamin or hormone deficiencies, the symptoms may resolve once the problem has been corrected. Therefore, dementia symptoms require comprehensive evaluation, so as not to miss potentially reversible conditions. The frequency of "treatable" causes of dementia is believed to be about 20%.

What Causes Dementia?

The most common causes of dementia include:

  • Degenerative neurological diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease (a rare inherited disorder), and some types of multiple sclerosis
  • Vascular disorders, such as multi-infarct dementia, which is caused by multiple strokes in the brain
  • Traumatic brain injury caused by motor vehicle accidents, falls, etc.
  • Infections of the central nervous system such as meningitis, HIV, and Creutzfeldt-Jakob disease, a quickly progressing and fatal disease that is characterized by dementia and muscle twitching and spasm
  • Chronic alcohol or drug use
  • Depression
  • Certain types of hydrocephalus, an excess accumulation of fluid in the brain that can result from developmental abnormalities, infections, injury, or brain tumors

Types of Dementia

Dementia can be split into two broad categories -- the cortical dementias and the subcortical dementias -- based on which part of the brain is affected.

  • Cortical dementias arise from a disorder affecting the cerebral cortex, the outer layers of the brain that play a critical role in thinking abilities like memory and language. Alzheimer's and Creutzfeldt-Jakob disease are two forms of cortical dementia. People with cortical dementia typically show severe memory loss and aphasia -- the inability to recall words and understand language.
  • Subcortical dementias result from dysfunction in the parts of the brain that are beneath the cortex. Usually, the forgetfulness and language difficulties that are characteristic of cortical dementias are not present. Rather, people with subcortical dementias, such as Parkinson's disease, Huntington's disease, and AIDS dementia complex, tend to show changes in their speed of thinking and ability to initiate activities.

There are cases of dementia where both parts of the brain tend to be affected, such as multi-infarct dementia.

Today on WebMD

nerve damage
Learn how this disease affects the nervous system.
senior woman with lost expression
Know the early warning signs.
woman in art gallery
Tips to stay smart, sharp, and focused.
medical marijuana plant
What is it used for?
senior man
boy hits soccer ball with head
red and white swirl
marijuana plant
brain illustration stroke
nerve damage
Alzheimers Overview
Graphic of number filled head and dna double helix