After eliminating other causes of memory loss, a physician will consider irreversible dementias as possible diagnoses. These include Alzheimer’s disease, vascular dementia, dementia with Lewy bodies, frontotemporal dementia, Parkinson’s disease and Huntington’s disease.
Other potential causes of irreversible dementias include infectious diseases (such as Creutzfeldt-Jakob disease) and amnesia.
After Alzheimer’s disease, the most common cause of significant memory loss is vascular dementia—a disorder often resulting from a series of tiny strokes (known as infarcts) that destroy brain cells. Each small infarct may be inconsequential alone, but the cumulative effect of many infarcts can destroy enough brain tissue to impair memory, language and other intellectual abilities. Other causes include cerebral amyloid angiopathy, in which the amyloid protein is deposited along blood vessels and causes them to rupture, and vasculitis, in which blood vessels become inflamed. This results in narrowing of the blood vessels and a weakening of the blood vessel walls, a risk factor for stroke.
Symptoms of vascular dementia often develop suddenly, and they are not limited to brain functions. Noncognitive hallmarks of vascular dementia include loss of bladder or bowel control (incontinence), a mask-like facial expression, and weakness or paralysis on one side of the body.
Vascular disease accounts for 10 to 20 percent of all dementia cases. Vascular dementia can also result from the vasculitis caused by lupus and other collagen-vascular diseases—and may be at least partially reversible in these conditions—as well as from a major stroke. Many people suffer from vascular dementia as a result of chronic high blood pressure, diabetes or coronary heart disease (a narrowing of the coronary arteries that reduces blood flow to the heart). People who survive a cardiac arrest can also suffer from memory deficits.
The drugs approved to treat Alzheimer’s disease are not approved for use in people with vascular dementia, and the evidence that they are beneficial is weak. An article published in Neurological Research, for example, concluded that the Alzheimer’s drugs donepezil (Aricept), rivastigmine (Exelon) and galantamine (Razadyne) appear to have benefits in people who have vascular dementia alone and in those who have it in conjunction with Alzheimer’s disease but because the diagnosis of vascular dementia is more difficult to make than Alzheimer’s disease, some individuals diagnosed with vascular dementia in those trials may have had only Alzheimer’s disease.
Results of a study reported in Alzheimer’s Disease and Associated Disorders suggest that memantine (Namenda) may have modest benefits in people with vascular dementia. Namenda belongs to a class of drugs known as NMDA receptor antagonists.
Dementia with Lewy bodies
Dementia with Lewy bodies accounts for 5 to 15 percent of dementia cases. This form of dementia shares characteristics and symptoms of both Alzheimer’s and dementia of Parkinson’s diseases. The disorder is named for the Lewy bodies—tiny deposits of a protein called alpha-synuclein—that are found throughout the brain.
People with this form of dementia tend to have problems with attention, visual hallucinations and some of the motor problems associated with Parkinson’s disease (such as shuffling gait, poor balance and stooped posture) early in the disease course. Sleep problems (excessive daytime drowsiness, very vivid dreams and leg kicks or arm swings while asleep) are common and may start years before any memory symptoms are noticed.
Cholinesterase inhibitors and the Parkinson’s drug levodopa (Larodopa) may be used to treat the symptoms. As with Alzheimer’s, none of those medications slows the progression of the disease. Antipsychotic drugs should not be prescribed or should be used with extreme caution because they can cause severe stiffness or tremor. As with Alzheimer’s, none of these medications slows the progression of the disease.
Frontotemporal dementia is much less common and less well known than Alzheimer’s disease, accounting for 5 percent of dementia cases. It affects the front (frontal lobes) and side (temporal lobes) of the brain and may spare memory for several years. It affects men and women equally, usually starting between ages 40 and 65, and progresses more rapidly than Alzheimer’s.
Frontotemporal dementia has several forms and causes, but personality changes or problems with language are usually the earliest symptoms. About one-third of cases have an identifiable genetic cause.
A person with the frontal or behavioral type of dementia may exhibit bizarre or out-of-character behavior, including reckless spending, gambling, shoplifting, making inappropriate comments or engaging in repetitive behaviors. People with the temporal lobe form have problems expressing or understanding spoken language.
Pick’s disease is the term used to describe the disease in the past. It was named for the pathological abnormality seen in some cases, but only found in approximately one-third of frontotemporal dementia cases. Symptoms include personality changes, inability to make plans and set goals, unawareness of any loss of mental function and language difficulties (aphasia). Palilalia (prominent repetition of a word or phrase with increasing rapidity) sometimes occurs later in the illness. The course of Pick’s disease can vary from two to 10 years, but it is ultimately fatal.
Recent studies suggest that five other neurological diseases associated with dementia may involve abnormalities similar to those of frontotemporal dementia. These include corticobasal ganglionic degeneration, hippocampal sclerosis, motor neuron disease inclusion dementia, primary progressive aphasia and progressive supranuclear palsy.
Huntington’s disease is a rare hereditary disorder of the central nervous system characterized by uncontrollable movement and dementia. (In the past, the disease was called Huntington’s chorea, from the Greek word meaning “dance.”)
The illness begins gradually, usually between the ages of 30 and 40, and people can live with the disease for up to 20 years. Early signs of Huntington’s disease include changes in behavior and unusual, fidgety movements.
Symptoms may be mild enough for the disease to go unnoticed for several years. Eventually, however, twisting and jerking movements that spread to the entire body are followed by memory loss, confusion and hallucinations.
Huntington’s disease directly affects the parts of the brain that control coordination. Studies show a striking decrease in brain levels of the neurotransmitter gamma-aminobutyric acid (GABA), but it is unclear whether this change is a cause or effect of the disease.
In 1993, scientists identified the gene defect that causes Huntington’s disease. The gene is dominant, meaning that children with a parent who carries the defective gene have a 50 percent chance of inheriting that gene and developing Huntington’s disease. Everyone who has the Huntington’s gene will eventually develop the disease. Gene therapy could one day correct the defective gene, but currently no treatment is available.
Creutzfeldt-Jakob disease (CJD) is a rare, fatal brain disorder that causes rapidly progressing dementia. The disease affects about one in one million people worldwide each year, including 250 to 300 Americans.
CJD can be transmitted through infected tissue (usually through organ or tissue transplantation), can be inherited or can occur with no known explanation. CJD typically strikes people over age 60 and leads to death in about a year.
A disorder with similar symptoms appeared in England in the mid-1990s, about 10 years after an outbreak of bovine spongiform encephalopathy (BSE, or mad cow disease) in cattle. BSE was linked to cattle feed that contained infected animal tissue.
The human form of the disease, known as new variant CJD (vCJD), has been reported in about 150 people worldwide, most of whom have been under age 30. All are believed to have eaten tainted beef in Europe during the mad cow disease epidemic. The disorder progresses more slowly than classic CJD (about 14 months) but inevitably leads to death.
To date, no cases of vCJD have been reported in the United States. No treatments exist for classic CJD or vCJD.
The number of cases of vCJD has plummeted since laws were passed banning any animal remains in cattle feed. If a family member dies of suspected CJD or vCJD, an autopsy should be performed to determine the precise cause of death.
People with amnesia suffer severe memory loss but have normal intelligence.
The exotic nature of amnesia has long fascinated scientists and the public. In fact, research on a patient with amnesia provided the first direct evidence that structures in the temporal lobe (where the hippocampus is located) play an important role in memory.
Amnesia is caused by damage to the part of the temporal lobes closest to the middle of the brain and can result from an accident, severe alcoholism, prolonged low blood pressure or viral inflammation of the brain.
Brain damage from such injuries usually results in anterograde amnesia—an inability to remember anything occurring after the injury. Retrograde amnesia—a loss of memory from a time prior to the accident, such as childhood—is usually limited.