The most common causes of dementia are Alzheimer's disease, vascular dementia and lewy body dementia. There are also a number of very rare neurological diseases, such as Huntington's disease or rare diseases such as progressive supranuclear paralysis (PSP), corticobasal neurodegeneration (CBD), Creutzfeldt-Jakob disease (CJD) that can lead to dementia as well as amyloid lateral sclerosis (ALS).