My father has dementia. How do I know if its alzheimers or if something else is causing it?

Alzheimer’s disease causes the majority of dementia in the elderly (up to 75%) but it is a diagnosis of exclusion. There exist other etiologies dementia and The American Academy of Neurology recommends testing for reversible causes such as hypothyroidism and vitamin B12 deficiency. In addition, depression may be associated with symptoms of dementia (psychomotor slowing, forgetfulness) and psychiatric evaluation may be needed. A primary care physician will be able to perform a comprehensive evaluation and draw the appropriate labs for your father.