Dementia is the loss of cognitive functioning—thinking, remembering, and reasoning—and behavioral abilities to such an extent that it interferes with a person’s daily life and activities. Dementia ranges in severity from the mildest stage, when it is just beginning to affect a person’s functioning, to the most severe stage, when the person must depend completely on others for basic activities of daily living.
Many conditions and diseases cause dementia. The two most common causes of dementia are Alzheimer’s disease and vascular dementia. Other causes include dementia with Lewy bodies, frontotemporal lobar degeneration, Parkinson’s disease, normal pressure hydrocephalus, Huntington’s disease, and Creutzfeldt-Jakob disease.
In addition, some people have mixed dementia—a combination of two or more disorders, at least one of which is dementia. A number of combinations are possible. For example, some people have Alzheimer’s disease and vascular dementia at the same time.
What is Alzheimer’s disease?
Alzheimer’s disease (AD) is a progressive and irreversible brain disorder that is characterized by a steady decline in cognitive, behavioral, and physical abilities severe enough to interfere with daily life. Hallmark signs of Alzheimer’s disease are memory loss, disorientation, and diminished thinking ability followed by a downward spiral that includes problems with verbal expression, analytical ability, frustration, irritability, and agitation.
With disease progression, physical manifestations include loss of strength and balance, inability to perform simple tasks and physical activities, and incontinence. As more of the brain is affected, areas that control basic life functions such as swallowing and breathing become irreversibly damaged, ultimately leading to death.
Approximately 5.2 million Americans suffer from AD. It is estimated that 11% of people age 65 and older, and nearly one third of those over age 85, have AD. A new person develops Alzheimer’s disease every 68 seconds, and current projections indicate that this rate will increase to one new case every 33 seconds by 2050.
Ultimately the disease is fatal, with death typically occurring 4 to 8 years after diagnosis, although some patients live for 20 years. AD is the sixth leading cause of death in the United States (Alzheimer’s Association: 2013 Alzheimer’s Association facts and figures report. www.alz.org/downloads/facts_figures_2013.pdf). Alzheimer’s disease is the only cause of death among the top 10 in United States that cannot be prevented or cured, or its progression even slowed. The burden of care for the patient with AD on the family, caregivers, and society is staggering. AD has often been referred to as the “long good-bye” or “death in slow motion
In 2012, there were an estimated 15.4 million unpaid caregivers of individuals with Alzheimer’s disease in the United States, most of whom were family members. These individuals provide an estimated 17.5 billion hours of unpaid care.
Vascular dementia (also called multi-infarct dementia), the second most common form of dementia, results from interrupted blood flow to the brain, often after a stroke or series of strokes. The symptoms can be similar to those of Alzheimer’s, and both conditions can occur at the same time.
Alzheimer’s disease and vascular disease-associated cognitive impairment are closely intertwined. For example, a large proportion of people diagnosed with Alzheimer’s also have brain damage due to vascular disease. In addition, many of the major risk factors for vascular disease (such as diabetes, heart disease) may also be risk factors for Alzheimer’s disease. The overlap between the two may be important because drugs and lifestyle modifications known to be effective in preventing vascular disease, such as controlling high blood pressure, lowering cholesterol, and engaging in physical activity, may also help prevent Alzheimer’s disease.
Dementia with Lewy Bodies
Dementia with Lewy bodies (DLB) is another common cause of dementia in older people. In DLB abnormal structures (microscopic deposits of abnormally aggregated proteins), called Lewy bodies, build up in areas of the brain. The disease may cause a wide range of symptoms, including changes in alertness and attention, hallucinations, confusion, and loss of memory. In addition they have parkinsonian symptoms such as problems with movement and posture and muscle rigidity. Lewy body disease can be hard to diagnose because both Parkinson’s disease and Alzheimer’s disease cause similar symptoms.
Frontotemporal Lobar Degeneration
Frontotemporal lobar degeneration (FTLD) is a clinical syndrome associated with shrinking of the frontal and temporal anterior lobes of the brain. Gradually, this damage causes difficulties in thinking and behaviors controlled by these parts of the brain. Many possible symptoms can result, including strange behaviors, emotional problems, trouble communicating, or difficulty with walking and other basic movements.
In Pick’s disease, one type of FTLD, the brain has abnormal microscopic deposits called Pick bodies (though these are not always present). FTLD is often misdiagnosed as a psychiatric problem or as AD. However, FTLD tends to occur at a younger age than does AD, typically between ages 40 and 70. The major distinguishing characteristic between these disorders and AD is marked symmetric lobar atrophy of the temporal and/or frontal lobes.
Secondary Diagnoses of Dementia
Dementia may occur in patients who have other disorders that primarily affect movement or other functions. These cases are often referred to as secondary dementias. The relationship between these disorders and the primary dementias is not always clear. For instance, people with advanced Parkinson’s disease, which is primarily a movement disorder, sometimes develop symptoms of dementia. Many Parkinson’s patients also have amyloid plaques and neurofibrillary tangles like those found in AD. The two diseases may be linked in a yet-unknown way, or they may simply coexist in some people. People with Parkinson’s and associated dementia sometimes show signs of Lewy body dementia or progressive supranuclear palsy at autopsy, suggesting that these diseases may also overlap with Parkinson’s or that Parkinson’s is sometimes misdiagnosed.
Other disorders that may include symptoms of dementia include multiple sclerosis; presenile dementia with motor neuron disease, also called ALS dementia; olivopontocerebellar atrophy (OPCA); Wilson’s disease; and normal pressure hydrocephalus (NPH).