Semantic dementia: a unique clinicopathological syndrome.

Semantic dementia (SD), one of the main clinical variants of frontotemporal dementia, presents a unique combination of clinical and imaging abnormalities. We describe the epidemiological, cognitive, and radiological features of SD. The distinctive and consistent neuropsychological deficits in this disorder have had a major effect on current conceptions of the organisation of semantic memory and its links to episodic memory, language, and perceptual processes. Structural (MRI) and functional (fluorodeoxyglucose-PET) studies in SD emphasise the role of the temporopolar and perirhinal cortices. Unlike other frontotemporal dementia syndromes, the neuropathological findings in SD are fairly predictable: most patients have ubiquitin-positive, tau-negative neuronal inclusions.