Causes of Dementia
Dementia has many forms and a variety of causes. A great deal of
progress has been made in dementia research, but scientists still do not
understand all of the causes of dementia. Below, you’ll find some of the known
and suspected causes of some common types of dementia.
Alzheimer’s Disease (AD)
Association estimates that Alzheimer’s disease (AD) causes 50 to 80 percent
of all dementia. The exact cause of AD
isn’t known, but there are some hypotheses.
Abnormal Buildup in the Brain
The buildup of two abnormal
structures in the brain (amyloid plaques and neurofibrillary tangles) is common
in AD and may be part of the cause.
Amyloid plaques are
clumps of beta-amyloid. Beta-amyloid is a piece of a protein that is found in
the normal brain. However, in AD, these beta-amyloid proteins clump together
forming plaques that can disrupt communication between nerve cells and cause
brain inflammation. People with AD have an abundance of these plaques in their
hippocampus, which is a part of the brain that is involved in memory. One
aspect of memory that is frequently disrupted in AD is the transfer of
short-term memories into long-term memories.
Neurofibrillary tangles are
fibrous tangles of an abnormal protein called tau. Tau is an important
fiber-like protein that keeps microtubules in the brain stable. These
microtubules transport nutrients, molecules, and information to other cells. When
tau is harmfully altered (possibly because of a genetic mutation), the fibers
get tangled and twisted up together. This causes the microtubules to become
unstable and disintegrate. This, in turn, collapses the whole neuron transport
A few people develop AD as young
as their early 30s and 40s. This is known as early onset Alzheimer’s disease. There
are three known gene mutations (defects) that are believed to be involved in
the formation of the amyloid plaques in early onset AD. These
three gene mutations do not play a role in the more common type of AD
(sometimes referred to as “late onset” Alzheimer’s disease).
AD and other dementias are
associated with abnormal structures in the brain called inclusions. These
structures are made of various abnormal proteins. It is not clear whether these
structures cause the disease or are caused by the disease.
Lewy Body Dementia (LBD)
LBD is a
common type of progressive dementia. Abnormal structures in the brain called
Lewy bodies are characteristic of this disease. Lewy bodies are found in the
brain’s outer layer (cortex). The cortex is responsible for thinking,
perceiving, producing, and understanding language. Lewy bodies are also often
located in various parts of the brain stem — particularly the substantia nigra.
Here, nerve cells release essential neurotransmitters that help control
movement and coordination. Lewy bodies are also commonly found in the brains of
people with Parkinson’s disease.
Any condition that prevents normal blood flow to the brain can
cause vascular dementia. The brain requires an uninterrupted supply of oxygen
from the bloodstream. In the absence of oxygen, brain cells can’t function
properly. If the oxygen flow is interrupted long enough, those brain cells die.
There are several types of
vascular dementia. The causes and symptoms for each vary slightly. One type,
called multi-infarct dementia (MID), is caused by numerous small strokes in the brain. Dementia
is more common when the stroke takes place in the left hemisphere of the brain
and when the stroke involves the hippocampus.
Not all people who have a stroke develop vascular dementia.
Frontal Lobe Dementia
lobe dementia is a group of diseases that cause significant changes in behavior
and/or language capability. It is sometimes known as frontotemporal dementia.
diseases all involve the degeneration of brain cells located in the frontal and
temporal lobes of the brain. The frontal and temporal lobes are the areas of
brain behind the eyes and above the ears. These areas control personality,
judgment, emotions, and language. People with frontal lobe dementia rarely have
amyloid plaques but often have neurofibrillary tangles. Frontal lobe dementia often
runs in families, suggesting that genetics may be an important causal factor.
Pick’s disease is one type of frontal lobe dementia. Like other
forms of frontal lobe dementia, there appears to be a strong genetic component
to its causation. The brains of people with Pick’s disease have abnormal
structures called Pick bodies — mostly made of the protein tau — inside the neurons. Brain
cells loaded with Pick bodies tend to balloon up in size and then die,
ultimately leading to the characteristic shrinkage (atrophy) in the
frontotemporal regions of the brain.
Presently, there is no specific treatment available for any frontal lobe
Potentially Reversible Conditions
Many causes of dementia and dementia-like symptoms are
treatable. They may be reversible if caught early enough and if
appropriate treatment is administered. While not an exhaustive list, here are
some of the more common reversible conditions:
Deficiencies of thiamine (vitamin
B1) often result from chronic alcoholism and can seriously impair
mental abilities—particularly memories of recent events.
Severe deficiency of vitamin B6 can cause a multisystem illness (pellagra)
that may include dementia.
Deficiencies of vitamin B12 have been linked to dementia in some cases.
to lead, other heavy metals, or other poisonous substances can lead to symptoms
of dementia. These symptoms may or may not resolve after treatment, depending
upon how badly the brain is damaged.
who have abused substances such as alcohol and recreational drugs sometimes
display signs of dementia even after the substance abuse has ended. This
condition is known as substance-induced
Metabolic Problems and Endocrine Abnormalities
Thyroid problems can lead to
apathy, depression, or dementia.
Hypoglycemia, a condition in
which there is not enough sugar in the bloodstream, can cause confusion or
Too little or too much sodium or
calcium can trigger mental changes.
Some people have an impaired
ability to absorb vitamin B12. This creates a condition called
pernicious anemia that can cause personality changes, irritability, or
Prescribed medications can
sometimes lead to reactions or side effects called delirium that mimic
dementia. These dementia-like effects can occur in reaction to just one drug or
they can result from drug interactions. They may have a rapid onset or they may
develop slowly over time.
Illicit drugs can also lead to
delirium, which can appear similar to dementia.
Heart and Lung Problems
The brain requires a high level of oxygen in
order to carry out its normal functions. Conditions such as chronic lung
disease or heart problems that prevent the brain from receiving adequate oxygen
can starve brain cells and lead to the symptoms of delirium that mimic
Many infections can cause
neurological symptoms, including confusion or delirium, due to fever or other
side effects of the body’s fight to overcome the infection.
Meningitis and encephalitis,
which are infections of the brain or the membrane that covers it, can cause
confusion, impaired judgment, or memory loss.
Untreated syphilis can damage the nervous system and
In rare cases, Lyme
disease can cause
memory or thinking difficulties.
People in the advanced stages of AIDS may develop a form of dementia.
People with compromised immune
systems, such as those with leukemia (and AIDS), may develop an infection
called progressive multifocal leukoencephalopathy (PML). PML is caused by a
common human polyomavirus called the JC virus and leads to damage or
destruction of the myelin sheath that covers nerve cells. PML can lead to
confusion, difficulty with thinking or speaking, and other mental problems.
hematomas, or bleeding between the brain’s surface and its outer covering (the
dura), can cause dementia-like symptoms and changes in mental function.
Anoxia occurs when the brain is starved of oxygen. Anoxia may be
caused by many different problems. These include heart attack, heart surgery,
severe asthma, smoke or carbon monoxide inhalation, strangulation, or an
overdose of anesthesia. Recovery depends upon the duration of the oxygen