Alzheimer’s Disease and Other Dementias
Dementia is a general term for a group of brain disorders. Alzheimer’s disease is the most common type of dementia, accounting for 50 to 70 percent of cases. This fact sheet briefly discusses Alzheimer’s and some other dementias.
All types of dementia involve mental decline that:
• occurred from a higher level (for example, the person didn’t always have a poor memory)
• is severe enough to interfere with usual activities and daily life
• affects more than one of the following four core mental abilities
• recent memory (the ability to learn and recall new information)
• language (the ability to write or speak, or to understand written or spoken words)
• visuospatial function (the ability to understand and use symbols, maps, etc., and the brain’s ability to translate visual signals into a correct impression of where objects are in space)
• executive function (the ability to plan, reason, solve problems and focus on a task)
Although symptoms can vary widely, the first problem many people with Alzheimer’s notice is forgetfulness severe enough to affect their work, lifelong hobbies or social life. Other symptoms include confusion, trouble with organizing and expressing thoughts, misplacing things, getting lost in familiar places, and changes in personality and behavior.
These symptoms result from damage to the brain’s nerve cells. The disease gradually gets worse as more cells are damaged and destroyed. Scientists do not yet know why brain cells malfunction and die, but two prime suspects are abnormal microscopic structures called plaques and tangles.
Mild cognitive impairment (MCI)
In MCI, a person has problems with memory or one of the other core functions affected by dementia. These problems are severe enough to be noticeable to other people and to show up on tests of mental function, but not serious enough to interfere with daily life. When symptoms do not disrupt daily activities, a person does not meet criteria for being diagnosed with dementia. The best-studied type of MCI involves a memory problem.
Individuals with MCI have an increased risk of developing Alzheimer’s disease over the next few years, especially when their main problem involves memory. However, not everyone diagnosed with MCI progresses to Alzheimer’s or another kind of dementia.
Vascular dementia (VaD)
Many experts consider vascular dementia the second most common type, after Alzheimer’s disease. It
occurs when clots block blood flow to parts of the brain, depriving nerve cells offood and oxygen. If it develops soon after a single major stroke blocks a large blood vessel, it is sometimes called “post-stroke dementia.”
It can also occur when a series of very small strokes, or infarcts, clog tiny blood vessels. Individually, these strokes do not cause major symptoms, but over time their combined effect is damaging. This type used to be called “multi-infarct dementia.”
Symptoms of vascular dementia can vary, depending on the brain regions involved. Forgetfulness may or may not be a prominent symptom, depending on whether memory areas are affected. Other common symptoms include difficulty focusing attention and confusion. Decline may occur in “steps,” where there is a fairly sudden change in function.
People who develop vascular dementia may have a history of heart attacks. High blood pressure or cholesterol, diabetes or other risk factors for heart disease are often present.
In mixed dementia, Alzheimer’s disease and vascular dementia occur at the same time. Many experts believe mixed dementia develops more often than was previously realized and that it may become increasingly common as people age. This belief is based on autopsies showing that the brains of up to 45 percent of people with dementia have signs of both Alzheimer’s and vascular disease.
Decline may follow a pattern similar to either Alzheimer’s or vascular dementia or a combination of the two. Some experts recommend suspecting mixed dementia whenever a person has both (1) evidence of cardiovascular disease and (2) dementia symptoms that get worse slowly.
Dementia with Lewy bodies (DLB)
In DLB, abnormal deposits of a protein called alpha-synuclein form inside the brain’s nerve cells. These deposits are called “Lewy bodies” after the scientist who first described them. Lewy bodies have been found in several brain disorders, including dementia with Lewy bodies, Parkinson’s disease and some cases of Alzheimer’s.
Symptoms of DLB include:
• Memory problems, poor judgment, confusion and other symptoms that can overlap with Alzheimer’s disease
• Movement symptoms are also common, including stiffness, shuffling walk, shakiness, lack of facial expression, problems with balance and falls
• Excessive daytime drowsiness
• Visual hallucinations
• Mental symptoms and level of alertness may get better or worse (fluctuate) during the day or from one day to another
• In about 50 percent of cases, DLB is associated with a condition called rapid eye movement (REM) sleep disorder. REM sleep is the stage where people usually dream. During normal REM sleep, body movement is blocked and people do not “act out” their dreams. In REM sleep disorder, movements are not blocked and people act out their dreams, sometimes vividly and violently.
Parkinson’s disease (PD)
Parkinson’s is another disease involving Lewy bodies. The cells that are damaged and destroyed are chiefly in a brain area important in controlling movement. Symptoms
include tremors and shakiness; stiffness; difficulty with walking, muscle control, and balance; lack of facial expression; and impaired speech. Many individuals with Parkinson’s develop dementia in later stages of the disease.
Frontotemporal dementia (FTD)
FTD is a rare disorder chiefly affecting the front and sides of the brain. Because these regions often, but not always, shrink, brain imaging can help in diagnosis. There is no specific abnormality found in the brain in FTD. In one type called Pick’s disease, there are sometimes (but not always) abnormal microscopic deposits called Pick bodies.
FTD progresses more quickly than Alzheimer’s disease and tends to occur at a younger age. The first symptoms often involve changes in personality, judgment, planning and social skills. Individuals may make rude or off-color remarks to family or strangers, or make unwise decisions about finances or personal matters. They may show feelings disconnected from the situation, such as indifference or excessive excitement. They may have an unusually strong urge to eat and gain weight as a result.
Creutzfeldt-Jakob disease (CJD)
Creutzfeldt-Jakob disease (pronounced CROYZ-felt YAH-cob) is a rare, rapidly fatal disorder affecting about 1 in a million people per year worldwide. It usually affects individuals older than 60. CJD is one of the prion (PREE-awn) diseases. These disorders occur when prion protein, a protein normally present in the brain, begins to fold into an abnormal three-dimensional shape. This shape gradually triggers the protein throughout the brain to fold into the same abnormal shape, leading to increasing damage and destruction of brain cells.
Recently, “variant Creutzfeldt-Jakob disease” (vCJD) was identified as the human disorder believed to be caused by eating meat from cattle affected by “mad cow disease.” It tends to occur in much younger individuals, in some cases as early as their teens.
The first symptoms of CJD may involve impairment in memory, thinking and reasoning or changes in personality and behavior. Depression or agitation also tend to occur early. Problems with movement may be present from the beginning or appear shortly after the other symptoms. CJD progresses rapidly and is usually fatal within a year.
Normal pressure hydrocephalus (NPH)
Normal pressure hydrocephalus (high-droh-CEFF-a-luss) is another rare disorder in which fluid surrounding the brain and spinal cord is unable to drain normally. The fluid builds up, enlarging the ventricles (fluid-filled chambers) inside the brain. As the chambers expand, they can compress and damage nearby tissue. “Normal pressure” refers to the fact that the spinal fluid pressure often, although not always, falls within the normal range on a spinal tap.
The three chief symptoms of NPH are (1) difficulty walking, (2) loss of bladder control and (3) mental decline, usually involving an overall slowing in understanding and reacting to
information. A person’s responses are delayed, but they tend to be accurate and appropriate to the situation when they finally come.
NPH can occasionally be treated by surgically inserting a long thin tube called a shunt to drain fluid from the brain to the abdomen. Certain television broadcasts and commercials have portrayed NPH as a highly treatable condition that is often misdiagnosed as Alzheimer’s or Parkinson’s disease. However, most experts believe it is unlikely that significant numbers of people diagnosed with Alzheimer’s or Parkinson’s actually have NPH that could be corrected with surgery. NPH is rare, and it looks different from Alzheimer’s or Parkinson’s to a physician with experience in assessing brain disorders. When shunting surgery is successful, it tends to help more with walking and bladder control than with mental decline.
Huntington’s disease (HD)
HD is a fatal brain disorder caused by inherited changes in a single gene. These changes lead to destruction of nerve cells in certain brain regions. Anyone with a parent with Huntington’s has a 50 percent chance of inheriting the gene, and everyone who inherits it will eventually develop the disorder. In about 1 to 3 percent of cases, no history of the disease can be found in other family members. The age when symptoms develop and the rate of progression vary.
Symptoms of Huntington’s disease include twitches, spasms, and other involuntary movements; problems with balance and coordination; personality changes; and trouble with memory, concentration or making decisions.
Wernicke-Korsakoff syndrome is a two-stage disorder caused by a deficiency of thiamine (vitamin B-1). Thiamine helps brain cells produce energy from sugar. When levels of the vitamin fall too low, cells are unable to generate enough energy to function properly. Wernicke encephalopathy is the first, acute phase, and Korsakoff psychosis is the long-lasting, chronic stage.
The most common cause is alcoholism. Symptoms of Wernicke-Korsakoff syndrome include:
• confusion, permanent gaps in memory and problems with learning new information
• individuals may have a tendency to “confabulate,” or make up information they can’t remember
• unsteadiness, weakness and lack of coordination
If the condition is caught early and drinking stops, treatment with high-dose thiamine may reverse some, but usually not all, of the damage. In later stages, damage is more severe and does not respond to treatment.