Dementia is characterized by progressive deterioration of intellect, behavior, and personality due to diffuse brain disease, especially affecting the cerebral cortex and hippocampus. Memory impairment is required for diagnosis. Common causes include Alzheimer's disease, cerebrovascular disease, Lewy body disease, and frontotemporal dementia. Evaluation involves assessing cognitive function, neurological exam, imaging, and lab tests to identify underlying causes and rule out other conditions. There is no cure for dementia, but some types can be temporarily slowed with medications or treated if potentially reversible causes are identified.