Dementia is a general term describing a significant, global decline in cognitive functioning. The most common cause of Dementia is specific pathological condition called Alzheimer's Disease, which accounts for about 75% of all Dementia. There are many other Causes of Dementia besides Alzheimer's. So, while all patients with Alzheimer’s have Dementia, not all patients with Dementia have Alzheimer’s (just most of them).