Is it Alzheimer's or another dementia?
| January 1, 2007
In-Depth Report
Is it Alzheimer's or another dementia?
For physicians and families intent on pinning down a diagnosis, one major factor that complicates the clinical picture is the existence of so many kinds of dementia. More than 50 conditions can mimic or cause dementia. Alzheimer's disease is by far the most common intractable condition. But other causes of irreversible dementia include blood vessel disease (vascular cognitive impairment, Binswanger's dementia), other degenerative disorders (frontotemporal lobar degeneration, Parkinson's disease, Huntington's disease), slow-growing brain tumors, or infections of the central nervous system (Creutzfeldt-Jakob disease, AIDS dementia, neurosyphilis).
In some types of dementia, treatment will improve mental functioning, and in a small percentage, the dementia is completely reversible if treatment begins before permanent brain damage occurs. That's why it is important to report to a doctor any signs of dementia early in the process.
Reversible dementias
Reversible dementias are often easier to diagnose than irreversible dementias because they are usually accompanied by other, obvious symptoms. In the following conditions or situations, however, dementia may be the primary, or even the only, symptom. Proper treatment may improve or even restore cognitive functioning.
Delirium
Delirium causes changes in mental functioning that can closely resemble dementia, but there are two important differences: speed of onset and level of consciousness. The mental changes in delirium develop quickly, often in a matter of hours or days, and consciousness is either clouded or fluctuates between drowsiness and alertness. In contrast, dementia evolves over months or years and doesn't affect the level of consciousness.
Delirium is considered a medical emergency, in part because it's often the main expression of a sudden, life-threatening illness. Elderly people are also susceptible to delirium after surgery. Alcohol withdrawal syndrome presents the classic picture of delirium. Similarly, delirium can occur from abrupt withdrawal from barbiturates or benzodiazepines, a group of anti-anxiety drugs that includes diazepam (Valium), chlordiazepoxide (Librium), and alprazolam (Xanax).
Toxic reactions to drugs
Medications are common culprits in mental decline. With aging, the liver becomes less efficient at metabolizing drugs, and the kidneys eliminate them from the body more slowly. As a result, drugs tend to accumulate in the body. Elderly people in poor health and those taking several different medications are especially vulnerable.
The list of drugs that can cause delirium and dementia-like symptoms is long. It includes antidepressants, antihistamines, anti-Parkinson drugs, anti-anxiety medications, cardiovascular drugs, anticonvulsants, corticosteroids, narcotics, and sedatives.
Depression
People sometimes manifest dementia-like symptoms — forgetfulness, disorientation, inattentiveness, and slowed responses — when they are depressed. This so-called pseudodementia can masquerade as the depression that often accompanies Alzheimer's disease, but there are subtle differences. In pseudodementia, the depressed mood begins before there is any mental decline. Typically, the person complains about memory loss or lack of concentration, looks sad or worried, and speaks in a flat, expressionless tone. In Alzheimer's-related depression, the mental decline comes first, and the person usually tries to conceal memory problems, rather than call attention to them.
Vitamin B12 deficiency
Inadequate intake is rarely a cause of vitamin B12 deficiency because this vitamin is plentiful in eggs, dairy products, meat, fish, and poultry, and it's efficiently stored in the liver. Instead, deficiency usually occurs because an individual can't absorb the vitamin from food. Untreated B12 deficiency can have a variety of consequences, including pernicious anemia, a condition in which your body is unable to produce enough red blood cells (see Figure 5).
In older people, the first symptoms of pernicious anemia are often confusion, slowness, irritability, and apathy. Peripheral neuropathy — numbness and tingling in the feet and hands that grows progressively worse — is also a common symptom. However, B12 injections, if started early, can remedy these symptoms.
Figure 5: B12 deficiency can cause dementia
Dementia could be a symptom of pernicious anemia, a condition in which the bone marrow produces red blood cells that are larger than normal. There are also fewer cells than normal. Symptoms of pernicious anemia include yellowish skin, fatigue, shortness of breath, and headaches. Numbness or tingling in the hands and feet and trouble keeping balance are also common. Usually the B12 deficiency stems from an inability to absorb B12 , not a lack of B12 in the diet. |
Hydrocephalus
Hydrocephalus ("water on the brain") is an excess of cerebrospinal fluid around the brain. The fluid is secreted by the ventricles (cavities in the center of the brain). It circulates around the spinal cord and is absorbed by veins on the external surface of the brain. Congenital hydrocephalus is usually diagnosed shortly after birth, but normal-pressure hydrocephalus occurs in a small number of elderly people. This condition can result from head trauma, brain hemorrhage, or meningitis (inflammation of the membrane covering the brain), but most cases occur spontaneously without an obvious preceding illness.
In addition to developing dementia, people with this condition lose bladder control and walk in a slow, hesitant manner, as if their feet are stuck to the floor. A surgically implanted tube (shunt) that drains fluid from a cavity in the brain (the lateral ventricle) to the jugular vein or to the abdomen brings rapid improvement, provided treatment is started soon after the symptoms appear.
Tumors
Brain tumors can interfere with cognitive functioning and cause personality changes. Depending on their location, they can trigger other symptoms, such as headaches, seizures, or vomiting. But the first symptoms of slow-growing tumors frequently resemble dementia, especially in older people. Brain tumors may be malignant (cancerous) and therefore capable of invading surrounding tissue. Or they may be benign (self-contained).
Subdural hematomas
Hematomas are blood clots caused by bruising. When they are located in the subdural area, between the brain surface and the thin membrane that covers it (the dura), they can cause symptoms that mimic Alzheimer's disease. Such subdural hematomas can also be life-threatening, causing coma and death. Most subdural hematomas are caused by severe head trauma sustained in automobile crashes.
But elderly people sometimes develop subdural hematomas after a very minor (and, therefore, often forgotten) head injury. As blood oozes into a closed space, the hematoma enlarges and begins to interfere with brain function. Removing the clot within weeks of the injury may restore mental function. However, the symptoms often evolve so slowly that diagnosis is delayed for months.
Thyroid disease
An overproduction of thyroid hormones (hyperthyroidism) is commonly caused by Graves' disease, while an underproduction (hypothyroidism) usually results from Hashimoto's thyroiditis. Both disorders can cause dementia-like symptoms.
To diagnose hyperthyroidism, physicians use a simple blood test that measures levels of thyroid hormones. Surgically removing the thyroid or destroying it with radioactive iodine usually corrects the cognitive problems.
Hypothyroidism is diagnosed by measuring the level of thyroid-stimulating hormone circulating in the blood. Physicians usually recommend thyroid hormone replacement, but this treatment doesn't always reverse the dementia.
Alcoholism
Wernicke-Korsakoff syndrome, an irreversible state of confusion and amnesia in alcoholics, results from thiamine deficiency due to long-term malnutrition. But consuming excessive amounts of alcohol for a decade or more can also cause a dementia that resembles Alzheimer's disease. Memory, orientation, and attention are impaired, although verbal skills are not always severely affected. In this type of dementia, abstinence may partly restore mental functioning.
Irreversible dementias
Although there are many causes of irreversible dementia, the following conditions are among the most common. In some cases, prompt treatment can prevent further damage, but lost cognitive functioning cannot be restored.
Vascular cognitive impairment
This condition, also known as multi-infarct dementia and vascular dementia, is caused by multiple infarcts, sections of tissue — in this case, brain tissue — that have died because blood circulation is cut off. The decrease in blood flow is often due to atherosclerosis, the accumulation of fatty deposits on artery walls. Multi-infarcts essentially result from a series of many tiny strokes. Each stroke affects such a small area of the brain that at first there aren't any noticeable symptoms. Eventually, though, they can damage a substantial area of the brain, causing many symptoms (see Figure 6).
People with multi-infarct dementia usually have hypertension (high blood pressure), cardiovascular disease, diabetes, or a history of stroke. The classic symptom of multi-infarct dementia is an abrupt mental change, sometimes accompanied by paralysis or slurred speech. The mental deterioration proceeds in a "stairstep" pattern — a person suffers a sudden cognitive decline, the decline levels off, and then new infarcts cause another sudden decline.
Figure 6: Cumulative damage from tiny strokes
Multi-infarcts, areas of dead tissue caused by a series of tiny strokes, can cause irreversible dementia. Often, each tiny stroke goes unnoticed because it damages just a small part of the brain and doesn't cause any long-term impairment. While each individual stroke may not be apparent, the cumulative damage is. Once enough of the strokes occur, a significant portion of the brain is damaged and symptoms such as confusion, impairment in thinking, slurred speech, and paralysis may arise. |
Degenerative diseases
Most dementias are caused by degenerative diseases, conditions whose deterioration cannot be stopped. Alzheimer's disease is the degenerative disease that is most often responsible for dementia, causing more than 50% of cases. Frontotemporal lobar degeneration, Parkinson's disease, and Huntington's disease account for approximately 25% of all dementias.
Frontotemporal lobar degeneration. This group of diseases, formerly called Pick's disease, is characterized by atrophy of the front part of the brain, including the frontal and temporal lobes. It is a rare condition that is often confused with Alzheimer's disease because the symptoms are sometimes identical.
In cases of frontotemporal lobar degeneration, people exhibit symptoms such as prominent aphasia early in the illness; loss of inhibition, resulting in sociopathic or hypersexual behavior; loss of emotional responses such as fear; and compulsively putting objects in their mouths. The cause of frontotemporal lobar degeneration is unknown, but some variants can run in families, and it is sometimes associated with mutations in a particular gene.
Parkinson's disease. This is a movement disorder resulting from a deficiency of dopamine, a neurotransmitter involved in coordinating muscle activity as well as memory function. Its hallmarks include tremors, rigid limbs, and difficulty starting or stopping movement. Mild cognitive problems are common early in the disease, and dementia occurs in 30%–80% of Parkinson's patients in the late stages.
Some people with Parkinson's disease develop dementia because they also have Alzheimer's disease. In other cases, the dementia is associated with hallucinations and appears to be linked to damage in the limbic and cortical areas of the brain. This variant of Parkinson's is called Lewy body dementia. Drugs that increase dopamine transmission, such as levodopa (Sinemet), help control the physical symptoms of Parkinson's but don't improve mental function.
Huntington's disease. Huntington's disease is a rare inherited disorder linked to an abnormal gene on chromosome 4. Its symptoms include involuntary writhing movements and dementia, and they often begin between the ages of 20 and 40. Mental disturbances may occur before or after physical problems appear, and people are often difficult to care for because of their irritability, aggressiveness, and erratic behavior. Medications can control the movement and mood disorders, but they don't stop the disease from progressing.
Infectious dementias
Virtually any infectious agent that attacks the central nervous system can cause dementia.
Creutzfeldt-Jakob disease. This is a rare, rapidly progressive dementia caused by a type of infectious agent called a prion. The initial symptoms are fatigue and subtle changes in behavior. Typically, the disease progresses to movement problems, seizures, coma, and — within a year — death.
AIDS dementia. This form of dementia occurs in people with AIDS, caused by infection with the human immunodeficiency virus (HIV). The dementia can develop rapidly, sometimes in a matter of weeks, and consists of forgetfulness, inattentiveness, and thinking difficulties.
Neurosyphilis. Before the introduction of penicillin, up to 30% of dementia patients admitted to mental institutions had neurosyphilis. This disorder, which develops about 15 years after syphilis infection, is now rare.
Review Date: 2007-01-01
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