Semantic dementia

Semantic dementia
Classification and external resources
MeSH D003704

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 characterized as a primary progressive aphasia.[1][2][3]

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.[4]

SD is one of the three canonical clinical syndromes associated with frontotemporal lobar degeneration (FTLD). 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).[5]

It was first described by Arnold Pick in 1904 and in modern times was characterised by Professor Elizabeth Warrington in 1975,[6] however it was not given the name semantic dementia until 1989.[7] The clinical and neuropsychological features, and their association with temporal lobe atrophy were described by Professor John Hodges and colleagues in 1992.[8]

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 associative visual 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,[9] 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.[10] 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.[11] 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.[12]

Genetics

Of all the FTLD syndromes SD is least likely to run in families and is usually sporadic.[13]

Management

There is currently no known curative treatment for this condition. Supportive care is essential in what is a greatly debilitating problem.

See also

References

  1. ↑ Gorno-Tempini, M.L.; Hillis, A.E.; Weintraub, S.; et al. (March 2011). "Classification of primary progressive aphasia and its variants". Neurology. 76 (11): 1006–14. doi:10.1212/WNL.0b013e31821103e6. PMC 3059138Freely accessible. PMID 21325651.
  2. ↑ Bonner, M.F.; Ash, S.; Grossman, M. (November 2010). "The new classification of primary progressive aphasia into semantic, logopenic, or nonfluent/agrammatic variants". Curr Neurol Neurosci Rep. 10 (6): 484–90. doi:10.1007/s11910-010-0140-4. PMC 2963791Freely accessible. PMID 20809401.
  3. ↑ Harciarek, M.; Kertesz, A. (September 2011). "Primary progressive aphasias and their contribution to the contemporary knowledge about the brain-language relationship". Neuropsychol Rev. 21 (3): 271–87. doi:10.1007/s11065-011-9175-9. PMC 3158975Freely accessible. PMID 21809067.
  4. ↑ Wilson, Stephen. "The neural basis of surface dyslexia in semantic dementia". Oxford Journals. Retrieved 12 October 2011.
  5. ↑ Weder ND, Aziz R, Wilkins K, Tampi RR (2007). "Frontotemporal dementias: a review". Ann Gen Psychiatry. 6: 15. doi:10.1186/1744-859X-6-15. PMC 1906781Freely accessible. PMID 17565679.
  6. ↑ Warrington, E.K. (November 1975). "The selective impairment of semantic memory". Q J Exp Psychol. 27 (4): 635–57. doi:10.1080/14640747508400525. PMID 1197619.
  7. ↑ Snowden, J.S.; Goulding, P.J.; Neary, D. (1989). "Semantic dementia: a form of circumscribed cerebral atrophy". Behav Neurol. 2: 167–82.
  8. ↑ Hodges, J.R.; Patterson, K.; Oxbury, S.; Funnell, E. (December 1992). "Semantic dementia. Progressive fluent aphasia with temporal lobe atrophy". Brain. 115 (Pt 6): 1783–806. doi:10.1093/brain/115.6.1783. PMID 1486461.
  9. ↑ Warrington, E.K.; McKenna, P.; Orpwood, L. (April 1998). "Single word comprehension: a concrete and abstract word synonym test". Neuropsychological Rehabilitation. 8 (2): 143–54. doi:10.1080/713755564.
  10. ↑ Chan, D.; Fox, N.C.; Scahill, R.I.; et al. (April 2001). "Patterns of temporal lobe atrophy in semantic dementia and Alzheimer's disease". Annals of Neurology. 49 (4): 433–42. doi:10.1002/ana.92. PMID 11310620.
  11. ↑ Schroeter, M.L.; Raczka, K.K.; Neumann, J.; von Cramon, D.Y. (2007). "Towards a nosology for frontotemporal lobar degenerations – A meta-analysis involving 267 subjects.". NeuroImage. 36 (3): 497–510. doi:10.1016/j.neuroimage.2007.03.024. PMID 17478101.
  12. ↑ Davies, R.R.; Hodges, J.R.; Kril, J.J.; Patterson, K.; Halliday, G.M.; Xuereb, J.H. (September 2005). "The pathological basis of semantic dementia". Brain. 128 (Pt 9): 1984–95. doi:10.1093/brain/awh582. PMID 16000337.
  13. ↑ Goldman, J.S.; Farmer, J.M.; Wood, E.M.; et al. (December 2005). "Comparison of family histories in FTLD subtypes and related tauopathies". Neurology. 65 (11): 1817–9. doi:10.1212/01.wnl.0000187068.92184.63. PMID 16344531.

Further reading

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