Heterogeneity of cognitive profiles in dementias of the Alzheimer type: theoretical aspects and clinical consequences

Presently, Alzheimer's disease can only be diagnosed with the coexistence of clinical symptoms and the presence of neuropathological alterations. Thus, in the absence of pre mortem biological markers, cognitive deficits form the starting point and the basis of inclusion criteria on which the clinician relies in order to make a putative diagnose of dementia of the Alzheimer type (DTA). Cognitive deficits should thus be accurately described through neuropsychological testing since it is essential to identify the cognitive deterioration patterns of the patients--in terms of selective impairment of cognitive functions--as well as the evolution of these patterns. Regarding this issue, the classical teaching of the Geneva school has proposed a homogeneous deterioration of the aphasic-apraxicagnosic syndrome into four stages. However, recent work does not support this hypothesis. On the contrary, these studies tend to show the presence of heterogeneity in neuropsychological manifestations of the disease. The aim of the present paper is to provide a critical review of this topic through a brief survey of the classical work and research that have recently been conducted. An analysis of the possible candidates responsible for the existence of this heterogeneity of cognitive profiles is presented. Finally, theoretical implications and clinical repercussions are discussed.