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Semantic dementia (SD) is a syndrome of progressive loss of semantic knowledge for objects and people. International criteria propose that SD be included in the frontotemporal lobar degeneration syndromes, with progressive non-fluent aphasia and frontotemporal dementia (FTD). However, several related syndromes have been defined that clinically and conceptually share both similarities and differences with SD: fluent progressive aphasia, progressive prosopagnosia, temporal variant of FTD. In order to establish a French consensus for the diagnosis and modalities of evaluation and follow-up of SD, a working group, composed of neurologists, neuropsychologists and speech-therapists, was established by the Groupe de réflexion sur les évaluations cognitives (GRECO). New criteria were elaborated, based on clinical, neuropsychological, and imaging data. They define typical and atypical forms of SD. A diagnosis of typical SD relies on an isolated and progressive loss of semantic knowledge, attested by a deficit of word comprehension and a deficit of objects and/or people identification, with imaging showing temporal atrophy and/or hypometabolism. SD is atypical if the deficit of semantic knowledge is present only within a single modality (verbal versus visual), or if non-semantic deficits (mild and not present at onset) and/or neurological signs, are associated with the semantic loss.

Circumscribed atrophy of the frontal and temporal lobes (frontotemporal lobar degeneration) accounts for about one fifth of cases of primary degenerative dementia occurring before the age of 65. It produces three prototypical clinical syndromes. The most common is frontotemporal dementia, characterized by personality change and profound alteration in social conduct and associated with bilateral atrophy of the frontal and anterior temporal lobes. Progressive non-fluent aphasia is characterized by difficulty in verbal expression, anomia and phonemic errors in the presence of relative preservation of comprehension and associated with atrophy predominantly of the left hemisphere. In semantic dementia there is fluent speech with semantic errors and severely impaired comprehension and naming, together with a visual associative agnosia, resulting from bilateral atrophy of the inferior and middle temporal gyri. The clinical syndromes occur with either of two main histological types: prominent microvacuolar change, without specific histological features (frontal lobe degeneration-type), severe astrocytic gliosis with or without ballooned cells and inclusion bodies (Pick-type). To improve clinical recognition and advance understanding of this relatively common form of cerebral degeneration, members of an international workshop on Frontotemporal Lobar Degeneration developed consensus criteria, building upon earlier published clinical diagnostic guidelines for frontotemporal dementia. The consensus criteria reported here specify core and supportive features for each of the prototypical clinical syndromes: frontotemporal dementia, progressive aphasia and semantic dementia, as well as providing broad inclusion and exclusion criteria for the generic entity of frontotemporal lobar degeneration.