| Semantic dementia | |
| Classification and external resources | |
| MeSH | [1] |
|---|---|
Semantic dementia (SD) 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 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[1] but was not given the name semantic dementia until 1989.[2] 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.[3]
Contents |
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 dementia 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[4] 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.[5]
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.[6]
Genetics
Of all the FTLD syndromes SD is least likely to run in families and is usually sporadic.[7]
Management
There is currently no known curative treatment for this condition. Supportive care is essential in what is a greatly debilitating problem.
References
- ^ Warrington EK (Nov 1975). "The selective impairment of semantic memory". Q J Exp Psychol 27 (4): 635–57. doi:. PMID 1197619.
- ^ Snowden JS, Goulding PJ, Neary D (1989). "Semantic dementia: a form of circumscribed cerebral atrophy". Behav Neurol 2: 167–82.
- ^ Hodges JR, Patterson K, Oxbury S, Funnell E (Dec 1992). "Semantic dementia. Progressive fluent aphasia with temporal lobe atrophy". Brain 115 ((Pt 6)): 1783–806. doi:. PMID 1486461. http://brain.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=1486461.
- ^ Warrington EK, McKenna P, Orpwood L (Apr 1998). "Single word comprehension: a concrete and abstract word synonym test". Neuropsychological Rehabilitation 8 (2): 143–54. doi:. http://www.informaworld.com/smpp/content~content=a713755564~db=all~order=page.
- ^ Chan D, Fox NC, Scahill RI, et al. (Apr 2001). "Patterns of temporal lobe atrophy in semantic dementia and Alzheimer's disease". Ann Neurol. 49 (4): 433–42. doi:. PMID 11310620.
- ^ Davies RR, Hodges JR, Kril JJ, Patterson K, Halliday GM, Xuereb JH (Sep 2005). "The pathological basis of semantic dementia". Brain 128 (Pt 9): 1984–95. doi:. PMID 16000337.
- ^ Goldman JS, Farmer JM, Wood EM, et al. (Dec 2005). "Comparison of family histories in FTLD subtypes and related tauopathies". Neurology 65 (11): 1817–9. doi:. PMID 16344531.
External links
- FTD Support Forum
- The Association for Frontotemporal Dementias
- 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
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