The concept of dementia has evolved over the past decade from one of progressive global intellectual deterioration to more modern definitions such as ‘a syndrome consisting of progressive impairment in both memory and at least one of the following cognitive deficits: aphasia, apraxia, agnosia or disturbance in executive abilities, sufficient to interfere with social or occupational functioning, in the absence of delirium or major non-organic psychiatric disorders (e.g. depression, schizophrenia)’ (American Psychiatric Association, 1987). This change in emphasis reflects the fact that brain diseases which cause cognitive dysfunction result in very different patterns of neuropsychological impairment, and often begin relatively focally. As will become apparent below, even this modern definition still presents problems for the diagnosis of very early cases of Alzheimer's disease who may show only memory deficits. At the other end of the spectrum, patients with frontal type dementias may not show memory deficits until very late in the course of the disease.

In this chapter, the clinical process of making a diagnosis of dementia will first be addressed, and decisions made about whether the patient appears to have a cortical or subcortical dementia. This helps narrow down the possible causes. Particular emphasis will be placed on the neuropsychology of memory, since this is central to the diagnosis of dementia.

The diagnostic process involves the following questions:

1. (i) Does the patient have dementia?

2. (ii) If so, does the clinical picture broadly conform to the pattern of cortical or subcortical dementia?

3. (iii) Which particular disease process is giving rise to the dementia?