Alzheimer’s disease (AD): is the most common form of dementia, a neurological disease characterized by loss of mental ability severe enough to interfere with normal activities of daily living, lasting at least six months, and not present from birth. AD usually occurs in old age, and is marked by a decline in cognitive functions such as remembering, reasoning, and planning.
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.
Lewy body dementia (LBD): is a neurodegenerative disorder that can occur in persons older than 65 years of age, which typically causes symptoms of cognitive (thinking) impairment and abnormal behavioral changes.
Frontotemporal dementia (frontotemporal lobar degeneration): is an umbrella term for a diverse group of rare disorders that primarily affect the frontal and temporal lobes of the brain — the areas generally associated with personality and behavior. Also called Picks disease.
Definitions provided by Answers.com and the MayoClinic.com
