Fronto-temporal lobar degeneration
Frontotemporal lobar degeneration (FTLD) is the pathological description of a group of neurodegenerative disorders characterised by focal atrophy of the frontal and temporal cortices. The conditions grouped under this term vary from publication to publication, depending on whether clinical, pathological or genetic factors are used in the classification.
The term Pick disease should probably be avoided when discussing clinical presentation. Rather it should be reserved for the pathological entity characterised by Pick bodies.
It should also be noted that the term frontotemporal dementia (FTD) is used inconsistently in the literature, sometimes synonymously with behavioural variant frontotemporal dementia and other times to denote frontotemporal lobar degeneration (FTLD) more generally 2-3. As such it is also best avoided.
A convenient division based on clinical presentation is into behavioural and language variants. The former demonstrates predominantly frontal lobe changes whereas the latter has a predilection for the temporal lobe (particularly the left), and is further subdivided into a number of clinical distinct entities. As such frontotemporal lobar degeneration can be divided as follows 3-4:
- behavioural variant fronto-temporal lobar degeneration dementia (bvFTLD), (behavioural variant frontotemporal dementia)1
- language variant fronto-temporal lobar degeneration (lvFTLD), (primary progressive aphasia (PPA)6
As if this wasn't complicated enough, in addition to a broad division into behavioural (frontal) and language (temporal) variants, an anatomical variant of right temporal frontotemporal dementia has been described with relatively distinct clinicopathological presentation 7.
The majority of cases are sporadic, however 20-40% may relate to an autosomal gene. Typically FTLDs occur in younger patients than Alzheimer's, usually with onset between 40-60 years of age.
Given the difficulty in clearly defining this group, the incidence is similarly fuzzy, however it is thought to be the fourth most common cause of progressive dementia (after Alzheimer disease, vascular dementia and Lewy body dementia) accounting for up to 20% of cases.
Due to the prominent frontal lobe involvement, there tends to be more pronounced and earlier involvement of behaviour and language, whereas the decline in short term memory seen prominently in Alzheimer is seen much later in FTLD.
Although, as the name suggests, the frontal and temporal lobes are predominantly affected, there is often striking asymmetry both of involvement of frontal vs temporal lobes, and involvement of left and right hemispheres.
In addition the degree of frontostriatal dysfunction varies between the different FTLD subgroups, with behavioural variant frontotemporal dementia (bvFTD) having the greatest involvement. As a result the caudate heads tend to be reduced in size in these patients, to a much greater degree than in the language variants of frontotemporal dementia 5.
Neurodegenerative diseases are legion and their classification just as protean. A useful approach is to divide them according to underlying pathological process, although even using this schema, there is much overlap and thus resulting confusion.
neurodegenerative MRI brain (an approach)
- measurements and ratios
- midbrain to pons area ratio (for PSP)
- Magnetic Resonance Parkinsonism Index (MRPI) (for PSP)
- frontal horn width to intercaudate distance ratio (FH/CC) (for Huntington disease)
- intercaudate distance to inner table width ratio (CC/IT) (for Huntington disease)
- scoring systems
- measurements and ratios
- typical/classical Alzheimer disease
- variant (e.g. posterior cortical atrophy)
- chronic traumatic encephalopathy (CTE)
- corticobasal degeneration
- frontotemporal lobar degeneration (FTLD) (not all are tau)
- Pick disease
- progressive supranuclear palsy (PSP)
- Alzheimer disease
- cerebral amyloidosis
- spinocerebellar ataxias
- Huntington disease
- hereditary spastic paraplegia
- amyotrophic lateral sclerosis (ALS)
- clinically unclassifiable parkinsonism (CUP)
- Unverricht-Lundborg disease
- prion diseases (not always included as neurodegenerative)
- 1. Neary D, Snowden JS, Gustafson L et-al. Frontotemporal lobar degeneration: a consensus on clinical diagnostic criteria. Neurology. 1998;51 (6): 1546-54. Neurology (full text) - doi:10.1212/WNL.51.6.1546 - Pubmed citation
- 2. The neuropathology of dementia. Cambridge University Press. ISBN:0521819156. Read it at Google Books - Find it at Amazon
- 3. Krishnamoorthy ES, Prince MJ, Cummings JL. Dementia, A Global Approach. Cambridge University Press. (2010) ISBN:0521857767. Read it at Google Books - Find it at Amazon
- 4. Growdon JH, Rossor M. The Dementias 2. Butterworth-Heinemann. (2007) ISBN:075067542X. Read it at Google Books - Find it at Amazon
- 5. Looi JC, Lindberg O, Zandbelt BB et-al. Caudate nucleus volumes in frontotemporal lobar degeneration: differential atrophy in subtypes. AJNR Am J Neuroradiol. 2008;29 (8): 1537-43. doi:10.3174/ajnr.A1168 - Pubmed citation
- 6. Gorno-tempini ML, Hillis AE, Weintraub S et-al. Classification of primary progressive aphasia and its variants. Neurology. 2011;76 (11): 1006-14. doi:10.1212/WNL.0b013e31821103e6 - Free text at pubmed - Pubmed citation
- 7. Josephs KA, Whitwell JL, Knopman DS et-al. Two distinct subtypes of right temporal variant frontotemporal dementia. Neurology. 2009;73 (18): 1443-50. doi:10.1212/WNL.0b013e3181bf9945 - Free text at pubmed - Pubmed citation