Semantic dementia
Encyclopedia
Semantic dementia is a progressive neurodegenerative disorder characterized by loss of semantic memory
in both the verbal and non-verbal domains. The most common presenting symptoms are in the verbal domain however (with loss of word meaning) and it is therefore often characterized (incorrectly) as a primary language disorder (a so-called progressive fluent aphasia).
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.
SD is one of the three canonical clinical syndromes associated with frontotemporal lobar degeneration
. 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).
It was first described by Arnold Pick in 1904 but in modern times was characterised by Professor Elizabeth Warrington
in 1975 but was not given the name semantic dementia until 1989. The association with temporal lobe atrophy was made by Professor John Hodges and colleagues in 1992 in a classic description of the clinical and neuropsychological features.
although cases have been described of 'pure' semantic dementia with few late behavioural symptoms.
Testing will also reveal deficits in picture naming (with semantic errors being made e.g. "dog" for a picture of a hippopotamus) and decreased category fluency.
Semantic memory
Semantic memory refers to the memory of meanings, understandings, and other concept-based knowledge unrelated to specific experiences. The conscious recollection of factual information and general knowledge about the world is generally thought to be independent of context and personal relevance...
in both the verbal and non-verbal domains. The most common presenting symptoms are in the verbal domain however (with loss of word meaning) and it is therefore often characterized (incorrectly) as a primary language disorder (a so-called progressive fluent aphasia).
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.
SD is one of the three canonical clinical syndromes associated with frontotemporal lobar degeneration
Frontotemporal lobar degeneration
-Further reading:*Hodges, John R. The Frontotemporal Dementia Syndromes. Cambridge University Press. 2007 ISBN 978-0-521-85477-1-External links:****Mayo Clinic - **...
. 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).
It was first described by Arnold Pick in 1904 but in modern times was characterised by Professor Elizabeth Warrington
Elizabeth Warrington
Elizabeth Warrington FRS, is a British neuropsychologist specialized in the study of dementia. She holds a PhD in visual processing and is now an emeritus professor of clinical neuropsychology at the University College London...
in 1975 but was not given the name semantic dementia until 1989. The association with temporal lobe atrophy was made by Professor John Hodges and colleagues in 1992 in a classic description of the clinical and neuropsychological features.
Signs and Symptoms
SD patients often present with the complaint of word-finding difficulties. Clinical signs include fluent aphasia, anomia, impaired comprehension of word meaning, and visual associative agnosia (inability to match semantically-related pictures or objects). As the disease progresses, behavioural and personality changes are often seen similar to those seen in frontotemporal dementiaFrontotemporal dementia
Frontotemporal dementia is a clinical syndrome caused by degeneration of the frontal lobe of the brain and may extend back to the temporal lobe...
although cases have been described of 'pure' semantic dementia with few late behavioural symptoms.
Neuropsychology
Patients perform poorly on tests of semantic knowledge. Published tests include both verbal and non-verbal tasks, e.g., The Warrington Concrete and Abstract Word Synonym Test, and The Pyramids and Palm Trees task (Howard and Patterson, 1992)Testing will also reveal deficits in picture naming (with semantic errors being made e.g. "dog" for a picture of a hippopotamus) and decreased category fluency.
Imaging
Structural MRI imaging shows a characteristic pattern of atrophy in the temporal lobes (predominantly on the left), with inferior greater than superior involvement and anterior temporal lobe atrophy greater than posterior. This distinguishes it from Alzheimer's disease. Meta-analyses on MRI and FDG-PET studies confirmed these findings by identifying alterations in the inferior temporal poles and amygdalae as the hotspots of disease - brain regions that have been discussed in the context of conceptual knowledge, semantic information processing, and social cognition. Based on these imaging methods, semantic dementia can be regionally dissociated from the other subtypes of frontotemporal lobar degeneration, frontotemporal dementia and progressive nonfluent aphasia.Pathology
The majority of patients with SD will have ubiquitin-positive, TDP-43 positive, tau-negative inclusions, although other pathologies have been described more infrequently, namely tau-positive Pick's disease and Alzheimer's pathology.Genetics
Of all the FTLD syndromes SD is least likely to run in families and is usually sporadic.Management
There is currently no known curative treatment for this condition. Supportive care is essential in what is a greatly debilitating problem.External links
- FTD Support Forum
- The Association for Frontotemporal Dementias
- The Bluefield Project to Cure Frontotemporal Dementia
- UCSF Memory and Aging Center and FTD videos
- Mayo Clinic - FTD Info
- Pick's Disease Support Group Online
- Frontotemporal Dementia Caregiver Support Center
- Prince of Wales Medical Research Institute
- FRONTIER the frontotemporal Dementia Research Group POWRI Sydney
See also
- Frontotemporal lobar degenerationFrontotemporal lobar degeneration-Further reading:*Hodges, John R. The Frontotemporal Dementia Syndromes. Cambridge University Press. 2007 ISBN 978-0-521-85477-1-External links:****Mayo Clinic - **...
- Frontotemporal dementiaFrontotemporal dementiaFrontotemporal dementia is a clinical syndrome caused by degeneration of the frontal lobe of the brain and may extend back to the temporal lobe...
- Progressive nonfluent aphasiaProgressive nonfluent aphasiaProgressive nonfluent aphasia is one of three clinical syndromes associated with frontotemporal lobar degeneration. The major symptom is progressive difficulties with the production of speech.-Clinical features:...
- Pick's diseasePick's diseasePick's disease, is a rare neurodegenerative disease that causes progressive destruction of nerve cells in the brain. Symptoms include loss of speech , and dementia. While some of the symptoms can initially be alleviated, the disease progresses and patients often die within two to ten years...
- Alzheimer's diseaseAlzheimer's diseaseAlzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
- Semantic memorySemantic memorySemantic memory refers to the memory of meanings, understandings, and other concept-based knowledge unrelated to specific experiences. The conscious recollection of factual information and general knowledge about the world is generally thought to be independent of context and personal relevance...
- Primary progressive aphasiaPrimary progressive aphasiaPrimary progressive aphasia is a type of dementia characterized most prominently by an insidious and progressive disorder of language and speech abilities...