ABSTRACT
Dementia is a ‘decline of intellectual function in comparison with the patient’s previous level of function’.1
This decline is usually associated with changes in behaviour and impairment of social and professional activities and is reflected in a decline in basic (BADL) and in instrumental (IADL) activities of daily living. About 5-10 per cent of the population over 65 has some kind of cognitive decline which is considered to be abnormal for this age group. Among these, more than 50 per cent will have a dementia of degenerative aetiology, of which the most common is Alzheimer’s disease (AD). However, recent studies have shown that in degenerative dementia it is common to have other pathologies as well, such as AD plus parkinsonian features, AD plus Lewy bodies, and more frequently, AD plus vascular pathology.2 The diagnosis of dementia is a clinical diagnosis,3 based on a careful clinical history and examination. Although investigations such as neuroimaging (computerized tomography (CT) and magnetic resonance imaging (MRI)) and laboratory tests are of value to rule out specific aetiologies, they are of no help for the diagnosis of dementia per se and even the aetiology may be suspected on clinical grounds in the majority of cases (see clinical differential features). Most often, the cognitive impairment in dementia is progressive, but a sudden onset does not exclude the diagnosis. The mode of onset and the knowledge of the clinical profile of a dementia syndrome are the basis for the differential diagnosis with respect to the likely aetiology. Although the criteria for the diagnosis of dementia demand multiple domains of cognitive impairment, isolated deficits such as amnesia, dyslexia or dysphasia may be the early manifestations of a dementing process. For example, early language disorder, although unusual in AD, may be the presentation of a particular subtype of AD (see
Chapter 5), although other progressive degenerative disorders such as primary progressive aphasia,4-7 the group of frontotemporal dementias (FTD) and the dementia of vascular aetiology, which may not have a sudden onset, enter the differential diagnosis. For that reason, the standard definition of dementia in the DSM-IV,8 that requires a memory deficit as the first criterion, should be modifed to include memory and/or any other predominant cognitive domain. In addition, mood and behaviour disturbances should be added as supportive features in the general definition of dementia. In the clinical situations of a progressive focal cognitive deficit, it is preferable to describe the clinical picture as a syndrome until the profile of cognitive impairment permits a more precise diagnosis.
