[Memory disorders in the elderly: complementary examinations--for whom?]

Recognizing the existence of memory disorders in elderly subjects necessarily involves developing a diagnostic strategy to identify the causes. Three types of complementary investigation are available: neurophysiological and neurobiological tests, and anatomical and functional brain imaging studies. Major efforts have been made to identify diagnostic markers on the electroencephalogram. Quantified EEG may have a certain value. However, it provides a plethora of data and there is no consensus on which items are most relevant on the EEG, whether the patient is awake or asleep. Evoked 'cognitive' potentials may also provide useful data, particularly to distinguish between the different types of degenerative dementia. Exaggerated pupil dilation in response to a mydriatric drug has also been put forward as a diagnostic test. The results, however, are controversial. For the time being there is no diagnostic laboratory parameter that can be used routinely, even if studies of the proteins tau and P97 are promising. Molecular genetics-based studies have identified a number of chromosomal abnormalities in certain families. Apart from studies of chromosome 19 and apolipoprotein 3, these markers have no practical utility. Allele sigma 4 is associated with a higher risk of Alzheimer's disease. Apolipoprotein E phenotyping can of course be of diagnostic value, but no more so than neuropsychological or neuroimaging methods. On the other hand, it is difficult to derive a predictive test. It also seems difficult to develop a diagnostic strategy without including brain imaging studies. The value of morphological imaging (CT, MRI) in the diagnosis of dementias is clear. Volumetric measurements of certain brain structures might be a useful diagnostic approach for early detection. Functional brain imaging methods (PET and SPECT) appear particularly suited to the diagnosis of degenerative dementias. The presence of functional abnormalities at onset, and, even before the first clinical signs appear, is clearly valuable.