Dementia Health Article

Definition

Dementia is a loss of mental ability severe enough to interfere with normal activities of daily living, lasting more than six months, not present since birth, and not associated with a loss or alteration of consciousness.

Description

Dementia is a group of symptoms caused by gradual death of brain cells. The loss of cognitive abilities that occurs with dementia leads to impairments in memory, reasoning, planning, and personality. While the over-whelming number of people with dementia are elderly, it is not an inevitable part of aging. Instead, dementia is caused by specific brain diseases. Alzheimer's disease is the most common cause, followed by vascular or multi-infarct dementia.

The prevalence of dementia has been difficult to determine, partly because of differences in definition among different studies, and partly because there is some normal decline in functional ability with age. Dementia affects 5–8% of all people between ages 65 and 74, and up to 20% of those between 75 and 84. Estimates for dementia in those 85 and over range from 30–47%. Between two and four million Americans have Alzheimer's disease; that number is expected to grow to as many as 14 million by the middle of the twenty-first century as the population as a whole ages.

The cost of dementia can be considerable. While most people with dementia are retired and do not suffer income losses from their disease, the cost of care is often enormous. Financial burdens include lost wages for family caregivers, medical supplies and drugs, and home modifications to ensure safety. Nursing home care may cost several thousand dollars a month or more. The psychological cost is not as easily quantifiable but can be even more profound. The person with dementia loses control of many of the essential features of his life and personality, and loved ones lose a family member even as they continue to cope with the burdens of increasing dependence and unpredictability.

Causes

Dementia is usually caused by degeneration of brain cells in the cerebral cortex, the part of the brain responsible for thoughts, memories, actions, and personality. Death of brain cells in this region leads to the cognitive impairment that characterizes dementia.

The most common cause of dementia is Alzheimer's disease (AD), accounting for half to three quarters of all cases. The brain of a person with AD becomes clogged with two abnormal structures, called neurofibrillary tangles and senile plaques. Neurofibrillary tangles are twisted masses of protein fibers inside nerve cells, or neurons. Senile plaques are composed of parts of neurons surrounding a group of proteins called beta-amyloid deposits. Why these structures develop is unknown. Current research indicates possible roles for inflammation, blood flow restriction, and accumulation of aluminum in the brain and toxic molecular fragments known as free radicals or oxidants.

Several genes have been associated with higher incidences of AD, although the exact role of these genes is still unknown. In 2001, investigators discovered a rare mutation in the amyloid precursor protein (APP) that is linked to early-onset Alzheimer's. The discovery points scientists to new ideas for targeting and treating the disease.

Vascular dementia is estimated to cause from 5–30% of all dementias. It occurs from a decrease in blood flow to the brain, most commonly due to a series of small strokes (multi-infarct dementia). Other cerebrovascular causes include: vasculitis from syphilis, Lyme disease, or systemic lupus erythematosus; subdural hematoma; and subarachnoid hemorrhage. Because of the usually sudden nature of its cause, the symptoms of vascular dementia tend to begin more abruptly than those of Alzheimer's dementia. Symptoms may progress stepwise with the occurrence of new strokes. Unlike AD, the incidence of vascular dementia is lower after age 75.

Other conditions which may cause dementia include:

• AIDS
• Parkinson's disease
• Lewy body disease
• Pick's disease
• Huntington's disease
• Creutzfeldt-Jakob disease
• brain tumor
• hydrocephalus
• head trauma
• multiple sclerosis
• prolonged abuse of alcohol or other drugs
• vitamin deficiency: thiamin, niacin, or B₁₂
• hypothyroidism
• hypercalcemia