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 features, and their association with temporal lobe atrophy were described by Professor John Hodges and colleagues in 1992. Presentation
The defining characteristic of SD is decreased performance on tasks that require semantic memory. This includes difficulty with naming pictures and objects, single word comprehension, categorizing, and knowing uses and features of objects. SD patients also have difficulty with spontaneous speech creation, using words such as "this" or "things" where more specific and meaningful words can be used. Syntax is spared, and SD patients have the ability to discern syntactic violations and comprehend sentences with minimal lexical demands. SD patients have selectively worse concrete word knowledge and association, but retain knowledge and understanding of abstract words. SD patients are able to retain knowledge of numbers and music, but have more difficulty with concrete concepts with visual associations. Impairments of processing of phonemic structure and prosodic predictability have also been observed. Genetics
The majority of SD patients have ubiquitin-positive, TDP-43 positive, tau-negative inclusions, although other pathologies have been described more infrequently, namely tau-positive Picks disease and Alzheimers pathology. Of all the FTLD syndromes, SD is least likely to run in families and is usually sporadic. Alzheimers Disease and Semantic Dementia
Alzheimers disease is related to semantic dementia, which both have similar symptoms.
has been used as a primary diagnostic technique for discerning how SD patients understand word meaning.Speech of SD patients is marked by word-finding pauses, reduced frequency of content words, semantic paraphasias, circumlocutions, increased ratios of verbs to nouns, increased numbers of adverbs, and multiple repeats.SD patients sometimes show symptoms of surface dyslexia, a relatively selective impairment in reading low-frequency words with exceptional or atypical spelling-to-sound correspondences.It is currently unknown why semantic memory is impaired and semantic knowledge deteriorates in SD patients, though the cause may be due to damage to an amodal semantic system. This theory is supported by the atrophy of the anterior temporal lobe, which is believed to contain a component of the semantic system that integrates conceptual information. Others hypothesize that the damage is predominantly to the ventral temporal cortex, since SD patients remember numbers and music, but have trouble associating visual cues to concrete words.Due to the variety of symptoms dementia patients present, it becomes more difficult to assess semantic memory capability especially with regard to musical elements. In order to circumvent the explicit verbal learning tests for dementia, semantic melodic matching is a useful technique for detecting the semantic memory of semantic dementia patients. Moreover, it is important to maintain that these tests must be compared to nonmusical domain tests, as music cognition is not often measured in semantic dementia patients (less data available).