Dementia is a clinical state characterised by a loss of function in at least two cognitive domains. When making a diagnosis of dementia, features to look for include memory impairment and at least one of the following: aphasia, apraxia, agnosia and/or disturbances in executive functioning. To be significant the impairments should be severe enough to cause problems with social and occupational functioning and the decline must have occurred from a previously higher level. It is important to exclude delirium when considering such a diagnosis.

When approaching the patient with a possible dementia, taking a careful history is paramount. Clues to the nature and aetiology of the disorder are often found following careful consultation with the patient and carer. A focused cognitive and physical examination is useful and the presence of specific features may aid in diagnosis. Certain investigations are mandatory and additional tests are recommended if the history and examination indicate particular aetiologies.

It is useful when assessing a patient with cognitive impairment in the clinic to consider the following straightforward questions:

• Is the patient demented?

• If so, does the loss of function conform to a characteristic pattern?

• Does the pattern of dementia conform to a particular pattern?

• What is the likely disease process responsible for the dementia?

An understanding of cognitive function and its anatomical correlates is necessary in order to ascertain which brain areas are affected. This, in turn, aids diagnosis. A discussion of the localisation of all cognitive processes is beyond the scope of this review. It is, however, particularly important to have an understanding of memory and its subdivisions, which is necessary to aid in differential diagnosis. We shall then illustrate how the history and examination, including bedside cognitive testing, are used in diagnosis.

TYPES OF MEMORY

When considering any memory disorder it is important to have an understanding …