Doctors have identified many other conditions that can cause dementia  or dementia-like symptoms.
Creutzfeldt-Jakob disease  (CJD). A rare brain disorder that affects about one in every million people worldwide each year, CJD belongs to a family of diseases known as the transmissible spongiform encephalopathies, or TSEs. Spongiform refers to the fact that the brain becomes filled with microscopic swellings that give the appearance of holes, like a sponge. CJD and other TSEs are believed to be caused by infectious proteins called prions that become misfolded. Scientists believe that the presence of misfolded prions can trigger normal proteins to misfold as well, causing a chain reaction. These abnormal prion proteins tend to clump together, which is believed to be related to the brain damage.
Symptoms usually begin after age 60, and most people die within a year of onset. In most cases, CJD occurs in people who have no known risk factors for the disease; however, an estimated 5 to 10 percent of cases in the U.S. are associated with genetic mutations. In addition, a type of CJD, called variant CJD (vCJD), has been found in Great Britain and several other European countries. vCJD has been observed to affect people who are younger than those with other forms of CJD and is believed to be caused by eating beef from cattle infected with a TSE called bovine spongiform encephalopathy, more commonly known as “mad cow disease.” Inherited forms of CJD include:
- Fatal familial insomnia. This prion disease causes a part of the brain involved in sleep to slowly degenerate. People with the disease have trouble sleeping and may show signs of poor reflexes and hallucinations.
- Gerstmann-Straussler-Scheinker disease. Symptoms include a loss of coordination (ataxia) and dementia that begin when people are 50 to 60 years old.
Huntington’s disease.  This hereditary disorder is caused by a faulty gene for a protein called huntingtin. Symptoms begin around age 30 or 40 years and include abnormal and uncontrollable movements called chorea, as well as gait changes and lack of coordination. Huntington’s disease may affect a person’s judgment, memory, and other cognitive functions. As the disease progresses, these cognitive problems worsen, and motor difficulties lead to complete loss of ability for self-care. Children of people with Huntington’s have a 50 percent chance of having the disorder.
Secondary dementias. These dementias occur in people with disorders that damage brain tissue. Such disorders may include multiple sclerosis ; meningitis; encephalitis ; and Wilson’s disease , in which excessive amounts of copper build up to cause brain damage. In rare cases, people with brain tumors may develop dementia because of damage to their brain circuits or a buildup of pressure inside the skull. Symptoms may include changes in personality, psychotic episodes, or problems with speech, language, thinking, and memory.
Chronic traumatic encephalopathy, initially known as dementia pugilistica, is caused by repeated traumatic brain injury  (TBI), such as in boxers or in people who suffered multiple concussions while playing a contact sport. People with this condition often develop poor coordination, slurred speech, and other symptoms similar to those seen in Parkinson’s disease, along with dementia, 20 years or more after the TBI events. This form of dementia also is characterized by brain atrophy and widespread deposits of tau aggregates. In some individuals, even just 5 to 10 years beyond the TBI events, behavioral and mood changes may occur.
Repeated concussions may cause chronic traumatic encephalopathy.
Dementia may not yet be present and the brain may not have atrophied, but small focal deposits of tau are seen in the brain at autopsy.
Subdural hematoma, or bleeding between the brain’s surface and its outer covering (the dura), is common in the elderly after a fall. Subdural hematomas can cause dementia-like symptoms and changes in mental function. With treatment, some symptoms can be reversed.
Many conditions that cause dementia can be reversed with the appropriate treatment.
- Cerebral vasculitis, an inflammation and necrosis (tissue death) of blood vessel walls, can cause a form of dementia that may resolve when the person is treated with immune suppressants.
- Some studies have shown that people with depression  are at increased risk of developing dementia. Severe depression can cause dementia and can be treated.
- Infections can cause confusion or delirium  due to related fever or other side effects associated with the body’s response to a foreign entity.
- Metabolic disorders of the nervous system, such as mitochondrial disorders, leukodystrophies, and lysosomal storage diseases, can lead to dementia.
- Metabolic problems and endocrine abnormalities such as thyroid problems, low blood sugar levels (called hypoglycemia), and low or high levels of sodium or calcium also may also cause dementia.
Brain scans can reveal the cause of dementia, which may be treatable.
- Nutritional deficiencies of vitamin B1 (thiamine), caused by chronic alcoholism, and vitamin B12 deficiencies can be reversed with treatment.
- Paraneoplastic syndromes (a group of symptoms that may develop when substances released by some cancer cells disrupt the normal function of surrounding cells and tissue) can cause symptoms that resemble dementia. Such symptoms generally occur in people with cancer when the body’s immune response to the cancer also ends up targeting proteins in the central nervous system. In many cases, the neurologic condition occurs before the cancer is detected. Circulating antibodies against brain proteins are common in both neurologic and cancer conditions.
- Side effects of medications or drug combinations may cause dementias that arise quickly or develop slowly over time.
Environmental factors may play a role in the development of certain types of dementia. This relationship is complex, however, since a person may carry genetic mutations that influence his or her response to environmental factors. Examples of environmental factors include:
Anoxia.  Anoxia and a related condition, hypoxia, are terms often used to describe a state in which there is a curtailed supply of oxygen to an organ’s tissues. Anoxia and hypoxia can lead to the loss of neurons and diffuse brain injury. Characteristics of the resulting dementia include confusion, personality changes, hallucinations, or memory loss. This type of dementia commonly occurs in people who survive cardiac arrest.
Poisoning. Exposure to lead, mercury, other heavy metals, or poisonous substances can lead to symptoms of dementia. These symptoms may or may not resolve after treatment, depending on how severely the brain is damaged.
Substance abuse. People who have abused substances such as alcohol  and recreational drugs sometimes display signs of dementia even after the substance abuse has stopped. This condition is known as substance-induced persisting dementia.
HIV-associated dementia (HAD) can occur in people who are positive for the human immunodeficiency virus , the virus that causes AIDS. HAD damages the brain’s white matter and leads to a type of dementia associated with memory problems, social withdrawal, and trouble concentrating. People with HAD may develop movement problems as well. The incidence of HAD has dropped dramatically with the availability of effective antiviral therapies for managing the underlying HIV infection.