Alzheimer's disease is the most common cause of dementia. However, other causes of dementia in the elderly can include:

Vascular dementia (abnormalities in the vessels that carry blood to the brain)
Lewy bodies variant (LBV), also called dementia with Lewy bodies
Parkinson's disease
Frontotemporal dementia
Vascular Dementia. Vascular dementia is primarily caused by either multi-infarct dementia (multiple small strokes) or Binswanger's disease (which affects tiny arteries in the midbrain).

Lewy Bodies Variant. Lewy bodies are abnormalities found in the brains of patients with both Parkinson's disease and Alzheimer's. They can also be present in the absence of either disease; in such cases, the condition is called Lewy bodies variant (LBV). In all cases, the presence of Lewy bodies is highly associated with dementia.

Parkinson's Disease. Some of the symptoms of Parkinson's disease and Alzheimer's can be similar and the diseases may coexist. However, unlike in Alzheimer's, language is not usually affected in Parkinson's related dementia.

Frontotemporal Dementia. Frontotemporal dementia (FTD) is a term used to describe several different disorders that affect the frontal and temporal lobes of the brain Although some of the symptoms can overlap with Alzheimer's, people who develop this condition tend to be younger than most patients with Alzheimer's disease.

Other Conditions. A number of conditions, including many medications, can produce symptoms similar to Alzheimer's. These conditions include severe depression, drug abuse, thyroid disease, vitamin deficiencies, blood clots, infections, brain tumors, and various neurological or vascular disorders.