According to the Mayo Clinic, dementia is a set of symptoms caused by conditions or changes in the brain that affect at least two brain functions severely enough to interfere with daily functioning. Symptoms may include memory loss, difficulty communicating, impaired judgment, personality changes, inability to reason and agitation. "Senile dementia" refers to dementia in people over the age of 65. Although Alzheimer's disease remains the most common type of dementia, several forms exist.
Alzheimer's Disease
According to the Fisher Center Foundation for Alzheimer's Research, Alzheimer's disease is the most common form of dementia affecting 4.5 to 4.7 million Americans. Alzheimer's disease results from the destruction of brain cells. Alzheimer's disease usually progresses slowly, over seven to 10 years, causing a gradual decline in cognitive abilities. Eventually, the affected part of the brain can not work properly because of limited functions, including those involving memory, movement, language, judgment, behavior and abstract thinking. Alzheimer's disease remains the most common cause of dementia in people age 65 and older.
Lewy Body Dementia
Lewy bodies, according to the Mayo Clinic, are abnormal clumps of protein that have been found in the brains of people with Lewy body dementia, Alzheimer's disease and Parkinson's disease. The symptoms of this dementia have similarities to Alzheimer's disease, but its unique features often include fluctuations in confusion and clear thinking (lucidity), visual hallucinations and Parkinson's-like tremors and rigidity.
Vascular Dementia
According to the Merck Manual, vascular dementia results from the destruction of brain tissue when the blood supply becomes reduced or blocked, usually due to several large strokes or many small ones. These strokes usually begin after age 70. Risk factors include high blood pressure, diabetes, irregular heart rhythms, high levels of fat in the blood and smoking. Even strokes that cause no physical symptoms can impair the brain tissue, leading eventually to vascular dementia. Often this dementia coexists with Alzheimer's disease.
Frontotemporal Dementia
The Mayo Clinic says that frontotemporal dementia includes a group of diseases characterized by the degeneration of nerve cells in the frontal and temporal lobes of the brain---the areas generally associated with personality, behavior and language. Signs and symptoms usually appear between the ages of 40 and 65, and may include socially inappropriate behaviors, loss of mental flexibility, language problems and difficulty with thinking and concentration.
Infectious Dementia
According to the AARP, virtually any infectious agent that attacks the central nervous system can cause dementia. Dementia can occur in people with AIDS, Creutzfeldt-Jakob disease and neurosyphilis.
Secondary Dementia
Secondary dementias occur in patients with other disorders that primarily affect movement, including Parkinson's disease, may eventually develop symptoms of dementia. The relationship between these disorders and dementia isn't completely understood, says the National Institute of Neurological Disorders and Stroke.
Reversible Dementia
According to the AARP, reversible dementias may result from by drug toxicity, Vitamin B12 deficiency, alcohol withdrawal, head trauma, brain hemorrhage, brain tumors or thyroid disease. Treatment of the underlying condition can result in a reversal of dementia symptoms. These dementias can occur in the elderly or in younger individuals.
