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Motor neurone disease, dementia and aphasia: coincidence, co-occurrence or continuum?
1MRC, Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge CB2 2EF, UK.
Abstract:
Cognitive, and particularly aphasic, symptoms associated with motor neurone disease (MND) are still frequently described as rare and "recently discovered". This review demonstrates that the association between MND and dementia was described and recognised as an entity as early as 1929, and its close relationship to Pick's disease was postulated in 1932. Changes in language production and comprehension were also observed by early authors, although they were rarely described as aphasia. The striking similarity to the contemporary descriptions is, however, sometimes obscured by diverging terminology. The syndromes of MND/dementia and MND/aphasia are well established but represent a comparatively small subgroup of MND. In addition, subtle cognitive alterations have also been reported in non-demented MND patients; most studies have found evidence of frontal-executive dysfunction, similar in pattern, but much milder than in patients with frank MND/dementia. These findings are strengthened further by post-mortem studies demonstrating pathological changes in the frontal lobes, and functional neuroimaging studies, showing reduced frontal activation. The issue of whether memory, visuospatial skills and language are affected in non-demented subjects remains, however, controversial. Further studies are required to establish whether MND/dementia and MND/aphasia form separate disease entities or can be viewed as extreme forms of a cognitive deficit characteristic of MND in general.
Insights
Cognitive and language changes in motor neurone disease (MND) have a long history, predating current descriptions. While MND with dementia or aphasia are recognized subgroups, milder cognitive deficits are common in non-demented patients.
Area of Science:
- Neurology
- Cognitive Science
Background:
- Cognitive and aphasic symptoms in motor neurone disease (MND) are often mischaracterized as rare or newly discovered.
- Historical reviews reveal that the association between MND and dementia was recognized as early as 1929, with links to Pick's disease noted in 1932.
- Early observations documented language changes in MND patients, though not always termed aphasia, with terminology differences sometimes obscuring historical connections.
Purpose of the Study:
- To review the historical context and current understanding of cognitive and language impairments in motor neurone disease (MND).
- To examine the relationship between MND, dementia, and aphasia, and to explore cognitive alterations in non-demented MND patients.
- To clarify whether MND-associated cognitive syndromes represent distinct entities or a spectrum of a broader deficit.
Main Methods:
- Literature review of historical and contemporary studies on cognitive and language deficits in motor neurone disease (MND).
- Analysis of early case reports and modern research, including post-mortem and functional neuroimaging studies.
- Synthesis of findings to evaluate the classification and spectrum of cognitive impairment in MND.
Main Results:
- The association of MND with dementia and aphasia has been documented since the early 20th century, challenging recent discovery claims.
- While MND/dementia and MND/aphasia are established subgroups, they represent a minority of cases.
- Non-demented MND patients frequently exhibit subtle frontal-executive dysfunction, supported by neuropathological and neuroimaging evidence of frontal lobe changes.
Conclusions:
- Cognitive and language impairments are integral features of motor neurone disease (MND) with a long-recognized history.
- Further research is needed to determine if MND-dementia and MND-aphasia are separate entities or extreme manifestations of a general cognitive deficit in MND.
- Frontal-executive dysfunction appears to be a common, albeit milder, feature in non-demented MND patients, indicating a broader spectrum of cognitive involvement.