A series of tests are therefore recommended which include neuropsychological profiles, brain imaging studies and laboratory investigations (see Table 6). These tests will help to determine the causes of dementia, exclude comorbid conditions and establish the underlying cause of the dementia.

An examination of the mental state may reveal evidence of self-neglect, concomitant physical illness and disinhibited or inappropriate behaviour, such as marked agitation, anxiety, irritability or retardation (both possibly indicating depression). Hostile or guarded behaviour may suggest underlying paranoid ideas, whereas a poor attention span may indicate clouding of consciousness and may be helpful in differentiating delirium from dementia. The patient’s speech may also reveal word-finding difficulties or evidence of aphasia or dysarthria.

Content of thought is also impoverished in dementia, but questioning may reveal the presence of delusions, perceptual disturbances, depressive ideas or the patient may elaborate on psychotic experiences, such as paranoia or misidentifications.

All patients presenting with dementia should undergo a cognitive assessment using the MMSE or similar tests to confirm a diagnosis and quantify the degree of cognitive impairment.

Neuropsychological profiles are different in cortical and subcortical types of dementia (see Table 5) and this can be informative in diagnosis and may help distinguish between AD or other dementias. For example, cortical dementias, such as AD, show impairments in cognitive abilities (ie, memory and language) and parietal lobe functions, such as praxis; therefore, impairment of day-to-day memory may suggest AD. In contrast, subcortical dementias, such as Parkinson’s disease, typically show a pattern of slowing, executive dysfunction and mild changes in memory.

The detection of characteristic abnormalities in AD and other neurodegenerative dementias on both structural imaging (MRI and CT) and functional imaging, such as SPECT and PET, can aid differential diagnosis. For example, CT scans can identify brain lesions (tumours), cerebral infarctions, subdural or extradural haematomas, cerebral abscesses and hydrocephalus, lobar cerebral atrophy, cerebrovascular disease and cortical atrophy (see Figure 2). MRI scans of patients with AD in the earliest stages can show evidence of atrophy of the hippocampus and medial temporal lobe, reflecting the underlying pathology (see Figure 3). MRI scans can identify lesions in cerebrovascular disease indicating vascular dementia (see Figures 4 and 5). Also, MRI scans may show knife-edge focal atrophy of frontal and/or temporal areas that is often asymmetrical indicating FTD (see Figure 6).

Laboratory investigations include routine biochemistry assays (see Table 6) to eliminate potentially treatable and reversible causes of dementia, such as metabolic, toxic or endocrine causes or drug reactions causing dementia symptoms.

Apolipoprotein E genotyping may be useful as an adjunct to clinical and radiological assessment in patients with definite dementia and uncertain AD, but ApoE assays are not predictive and should be avoided as a predictive test in asymptomatic patients, even those with familial risk of AD owing to a lack of sensitivity and specificity of the test.