Various Types and Causes of Dementia

There are several causes of dementia. Some causes may be reversible, such as the ones associated with certain medications, B12 deficiency, hypothyroidism, syphilis, depression, and normal pressure hydrocephalus. Other causes are not reversible and knowing which type of dementia a patient has can help physicians tailor their care appropriately.

Woman holding hands with an older man with other older adults in the background
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Alzheimer’s Disease

Alzheimer’s is the leading cause of dementia. It accounts for roughly two-thirds of dementia cases. Alzheimer’s is a progressive disease that is characterized by depositions of abnormal proteins in the brain in the form of plaques and tangles.

Scientists are still trying to figure out what causes Alzheimer’s. Advanced age, family history, and lifestyle factors such as smoking seem to influence a person’s risk of developing Alzheimer’s.

Vascular Dementia

Vascular dementia is the second most common cause of dementia. It results from reduced blood flow to the brain from either a narrowing or complete blockage of blood vessels that deprives blood cells of vital oxygen and nutrients. Vascular dementia is usually caused by multiple small strokes or sometimes by a single large stroke.

Frontotemporal Dementia

Frontotemporal dementia (FTD) is characterized by atrophy, or wasting away, of the frontal and temporal lobes of the brain in the absence of Alzheimer's. It usually occurs earlier than Alzheimer's disease with onset often occurring between 45 to 65 years old. It progresses more rapidly than Alzheimer's and has a shorter life expectancy. FTD may have a genetic link but scientists are still unsure of the exact cause.

FTD typically presents with behavioral changes, usually as inappropriate social or personal conduct. Problems with speech, called aphasia, is the other main presentation of FTD.

Lewy Body Dementia

Lewy body dementia, named for Friederich H. Lewy, who first described the deposits in the early 1900s, is characterized by deposits of the protein alpha-synuclein inside brain cells. While many symptoms of Lewy Body dementia resemble Alzheimer’s, three symptoms set it apart from other types of dementia: vivid hallucinations, varying levels of consciousness or alertness, and severe sleep disturbances.

Parkinson’s Disease

Parkinson’s disease is the progressive deterioration of the nerve cells in the brain that produce the important brain chemical dopamine. Dopamine works as a chemical messenger in the brain, coordinating smooth and balanced muscle movement. Without dopamine, the brain is unable to communicate adequately, leading to a loss of ability to control body movements.

In its advanced stages, Parkinson’s can affect cognitive functioning, leading to difficulty retrieving memories, problems with reasoning, decision making, and problem-solving, and depression. Dementia occurs in roughly 20% to 60% of patients with Parkinson’s disease.

Huntington’s Disease

Huntington’s disease is an inherited disease that usually occurs in a person’s 30s or 40s. It is characterized by uncontrolled movements, emotional disturbances, and mental deterioration. With Huntington’s disease, progressive mental deterioration with resultant dementia may be the first signs of the disease. Children with one parent who is diagnosed with Huntington’s gene have a 50% chance of developing the disease themselves.


HIV/AIDS is a virus that is contracted through contact with an infected person’s blood or body fluids. AIDS-related dementia may be related to CD4+ T-cell count nadir and duration of immunosuppression. Before antiretroviral therapy, AIDS-related dementia was linked to a low CD4+ count and high viral loads. Now, with effective antiretroviral therapy which slows the progress of HIV and AIDS, patients are living longer and aren't succumbing to opportunistic infections at the rate they once did. These patients may be at risk of developing AIDS-related dementia as they age.

Symptoms of AIDS-related dementia include symptoms forgetfulness, slowness, difficulties with concentration and problem solving, and hallucinations.

Creutzfeldt-Jakob Disease (CJD)

Most commonly known as Mad Cow disease, Creutzfeldt-Jakob disease (CJD) is caused by prions. These prions destroy the brain's ability to function. CJD may have a genetic link but most cases are sporadic with no known cause. Some cases may be the result of exposure to contaminated medical equipment during procedures. CJD-related dementia often progresses rapidly over several months and involves problems with attention, concentration, appetite, vision, and coordination.

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  • Alexander W Thompson, MD, MBA, Andrew A Pieper, MD, Ph.D., and Glenn J Treisman, MD, Ph.D. Dementia and delirium in HIV-infected patients.
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  • Marie-Florence Shadlen, MD and Eric B Larson, MD, MPH. Dementia Syndromes.

By Angela Morrow, RN
Angela Morrow, RN, BSN, CHPN, is a certified hospice and palliative care nurse.