Clinical features and assessment of severe dementia. A review.

Sound understanding of the dementia syndrome requires adequate acquaintance with its entire spectrum, from the lightest to the most advanced stages. Most studies of dementia deal with light to moderate stages of the condition, while relatively little attention has been paid to its most severe stages. This review presents a clinical description of patients with severe dementia and of the tests currently available to evaluate their cognitive, behavioural, and functional status. Available instruments such as the Hierarchic Dementia Scale or the Severe Impairment Battery now allow quantification of the cognitive and behavioural status of patients with severe dementia. Experience with severe dementia shows that, far from being in a "vegetative state", as is commonly thought, late-stage patients are in fact quite different from one another and in most cases continue to have an interaction with their environment. This ability to better define the characteristics of patients with severe dementia provides the basis for correlations between clinical data and data derived from neuroimaging, neurochemistry, or neuropathology. It also sets the stage for possible therapeutic trials involving these patients.