Semantic Dementia (SD) represents a rare variant of presenile primary degenerative diseases of "frontotemporal lobar degenerations" (FTLD). SD is characterized by anterior-temporal atrophy and a selective semantic deficit. Neuropsychological impairment either bears on fluent aphasia with marked naming and comprehension difficulties or on a disorder of object recognition or on both. Behavioural alterations such as stereotyped behaviour and change in food preference become prominent as the disease progresses and are interpreted as a correlative for the pathological spreading to frontal structures. Since SD is often misclassified as Alzheimer's disease (AD), but calls for a different management, diagnostic consensus criteria by Neary and colleagues are depicted. The neuropsychological profile is described in detail and complemented by a case report. Implications from the dissociation of disturbed memory systems of SD (semantic) and AD (episodic) for models of long-term memory are discussed in terms of connectivity in the medial temporal lobe. SD can contribute to a better understanding of the structure and organisation of the semantic system.

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