Semantic dementia

In neurology, semantic dementia (SD), also known as semantic variant primary progressive aphasia (svPPA), is a progressive neurodegenerative disorder characterized by loss of semantic memory in both the verbal and non-verbal domains. However, the most common presenting symptoms are in the verbal domain (with loss of word meaning). Semantic dementia is a disorder of semantic memory that causes patients to lose the ability to match words or images to their meanings. However, it is fairly rare for patients with semantic dementia to develop category-specific impairments, though there have been documented cases of it occurring. Typically, a more generalized semantic impairment results from dimmed semantic representations in the brain. SD is one of the three canonical clinical syndromes associated with frontotemporal lobar degeneration (FTLD), with the other two being frontotemporal dementia and progressive nonfluent aphasia. SD is a clinically defined syndrome but is associated with predominantly temporal lobe atrophy (left greater than right) and hence is sometimes called temporal variant FTLD (tvFTLD). SD is one of the three variants of primary progressive aphasia (PPA), which results from neurodegenerative disorders such as FTLD or Alzheimer's disease. The other two variants of primary progressive aphasia (PPA) are logopenic variant PPA (lvPPA) and confluent-agrammatic variant PPA (navPPA). There are distinctions between Alzheimer's disease and semantic dementia with regard to types of memory affected. In general, Alzheimer's disease is referred to as a disorder affecting mainly episodic memory, defined as the memory related to specific, personal events distinct for each individual. Semantic dementia generally affects semantic memory, which refers to long-term memory that deals with common knowledge and facts. SD was first described by Arnold Pick in 1904 and in modern times was characterized by Professor Elizabeth Warrington in 1975, but it was not given the name semantic dementia until 1989. The clinical and neuropsychological...