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International audience

International audience

International audience

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.

Primary progressive aphasia (PPA), initially described by Mesulam, is a syndrome of progressive deterioration of language, occurring in the presenium. Several classifications have been proposed, but the most useful one distinguishes non fluent and fluent forms of PPA. Both begin by anomia. In non fluent PPA, there is a progressive reduction of language, sometimes with aggramatism and articulatory impairment, but without impairment of comprehension. Fluent PPA is characterized by preserved fluency with severe impairment of single word comprehension. It is frequently confounded with semantic dementia (SD), but some observations can be differentiated from SD. After several years, all patients become mute, and most of them develop dementia, usually of frontal lobe type. The syndrome of PPA is due to neurodegenerative brain pathology affecting mostly the perisylvian regions of the left hemisphere. In most cases, no Alzheimer type pathology was found in the brain, but tauopathy (mainly in non fluent PPA) or motor neuron disease type pathology - tau negative ubiquitin inclusions (mainly in fluent PPA). However, Alzheimer type pathology was found in a substantial number of cases.

Predominant impairment or preservation of category-specific naming and comprehension is not rare in aphasics. Much less frequent is a selective inability to generate proper names. To our knowledge, only one such case has been reported after a left thalamic lesion, located in the ventral anterior nucleus, the mamillo-thalamic tractus and the genu of the internal capsule. We report a new case of selective inability to generate proper names after a left tubero-thalamic infarct. A 65-year old right-handed man presented with a selective impairment in producing proper names, both from photographs or descriptions and on tests of verbal fluency. The deficit was obvious both for persons names and for geographical names. The rest of the neuropsychological testing was remarkable only for a mild verbal amnesia, affecting only serial material (list of words), a reduced fluency for flowers, fruits and musical instruments, difficulties in learning of new words, and a dissociation between preserved learning for words on a test of learning of words and occupations (Cohen, 1990). This anomia for proper names could result from an indirect frontal-lobe dysfunction, preventing voluntary activation of the phonological representation of proper names.

A battery of tactile tests for the study of unilateral neglect is presented with the purpose of comparing the tactile modality to the visual modality. This was applied in 4 patients with right hemisphere lesions. In 3 patients, there was evidence of neglect in both modalities with qualitatively identical anomalies. The function of spatial manipulation involved in the tasks is stressed. In the cases where both modalities were involved a supramodal hemispatial disturbance is assumed.