Corticobasal Degeneration (CBD) is an neurodegenerative disorder, classified as an atypical parkinsonian syndrome (also known as one of the Parkinson's-plus syndromes). CBD was previously classified as a progressive asymmetric movement disorder characterized by akinesia, rigidity, dystonia, focal myoclonus, ideomotor apraxia, and/or alien-limb phenomena. However, it is increasingly seen as a disorder with cognitive and behavioural disturbances as well. The diagnosis of CBD remain challenging because there is considerable overlap between CBD pathology and other neurodegenerative disorders including progressive supranuclear palsy (PSP), Alzheimer's Disease (AD), and frontotemporal dementia.
Since CBD pathology overlaps with other neurodegenerative disorders, it is helpful to first think of CBD on spectrum of neurodegenerative syndromes. Thus the term Corticobasal Syndrome (not Corticobasal Degeneration), includes other neurodegenerative disorders such as progressive supranuclear palsy (PSP), Alzheimer's Disease (AD), and frontotemporal dementia (FTD) pathology.
| Syndrome | Features |
|---|---|
| Probable corticobasal syndrome | Asymmetric presentation of 2 of:a) limb rigidity or akinesia b) limb dystonia c) limb myoclonus Plus 2 of:d) orobuccal or limb apraxia e) cortical sensory deficit f) alien limb phenomena (more than simple levitation) |
| Possible corticobasal syndrome | May be symmetric: 1 of:a) limb rigidity or akinesia b) limb dystonia c) limb myoclonus Plus 1 of:d) orobuccal or limb apraxia e) cortical sensory deficit f) alien limb phenomena (more than simple levitation) |
| Frontal behavioral-spatial syndrome | 2 of:a) executive dysfunction b) behavioral or personality changes c) visuospatial deficits |
| Nonfluent/agrammatic variant of primary progressive aphasia | Effortful, agrammatic speech plus at least 1 of:a) impaired grammar/sentence comprehension with relatively preserved single word comprehension, or b) groping, distorted speech production (apraxia of speech) |
| Progressive supranuclear palsy (PSP) syndrome | 3 of:a) axial or symmetric limb rigidity or akinesia b) postural instability or falls c) urinary incontinence d) behavioral changes e) supranuclear vertical gaze palsy or decreased velocity of vertical saccades |
After thinking about the spectrum of symptoms that a patient may have, and ruling out other diagnoses on the differential, the following criteria can be used to determine whether a patient has corticobasal degeneration, as proposed by the 1st International CBD Investigators Meeting in 2013.[1]
| Clinical research criteria for probable sporadic CBD | Clinical criteria for possible CBD | |
|---|---|---|
| Presentation | Insidious onset and gradual progression | Insidious onset and gradual progression |
| Minimum duration of symptoms (year) | 1 | 1 |
| Age at onset (year) | ≥ 50 | No minimum |
| Family history (2 or more relatives) | Exclusion | Permitted |
| Permitted phenotypes (see previous table for criteria) | 1) Probable CBS or 2) FBS or NAV plus at least 1 CBS feature (a–f) | 1) Possible CBS or 2) FBS or NAV or 3) PSPS plus at least 1 CBS feature b–f |
| Genetic mutation affecting tau (e.g. - MAPT) | Exclusion | Permitted |
Pathological findings in CBD patients have shown astrocytic abnormalities in the brain as well as accumulation of tau protein. Thus, CBD is considered a tauopathy.
There is a broad differential diagnosis for CBD, because there is considerable overlap between CBD pathology and progressive supranuclear palsy (PSP), Alzheimer's Disease (AD), and frontotemporal dementia (FTD) pathology.
MRI shows frontal-parietal atrophy