Frontotemporal dementia, sometimes called frontal lobe dementia, describes a group of diseases characterized by degeneration of nerve cells - especially those in the frontal and temporal lobes of the brain. Unlike Alzheimer's disease, frontotemporal dementia usually does not include formation of amyloid plaques. In many people with frontotemporal dementia, there is an abnormal form of tau protein in the brain, which accumulates into neurofibrillary tangles. This disrupts normal cell activities and may cause the cells to die.