Assessment includes a detailed background. Every assessment has to include a collateral history from somebody who knows you well, because those around the patient see and may give a clearer picture.
The nuts and bolts of the assessment include a cognitive examination looking at several cognitive domains such as attention, memory, language, calculation, visuospatial function, executive function and praxis. The physical examination of the nervous system is done to look for any associated physical features that appear in disorders such as Lewy Body Dementia, Frontotemporal Dementia, and to identify anything that suggests a structural cause of cognitive change (e.g. growths within the skull vault).
Many people will not have any evidence of true cognitive dysfunctions once assessed and appropriately investigated. Investigations are also to identify potentially treatable/reversible causes of dementia (e.g. vitamin B12 deficiency, thyroid dysfunction, limbic encephalitis). Treating depression or changing lifestyle may resolve things.
Follow-up reassessment of those with a single cognitive domain abnormality after a year is helpful, but some may like to go on to have more detailed tests such as lumbar puncture (spinal tap) and PET brain imaging. These may be helpful in prediction of the risk of a true dementia if there is only one area of cognition affected on first assessment.
For more information on dementia: