Corticobasal syndrome

Corticobasal syndrome is a rare, progressive atypical Parkinsonism syndrome and is a tauopathy related to frontotemporal dementia. CBS is typically caused by the deposit of tau proteins forming in different areas of the brain.

Classification

CBS is the most common type of corticobasal degeneration although the terms CBD and CBS have been used interchangeably in the past. The other three phenotypes of CBD are:

frontal-behavioral dysexecutive-spatial syndrome
nonfluent/agrammatic variant of progressive aphasia, and
progressive supranuclear palsy.

Symptoms and signs

Symptoms of CBS include apraxia, alien limb phenomenon, frontal deficits, and extrapyramidal motor symptoms such as myoclonus or rigidity. Movement deficits often begin on one side and progress to the other.

Pathophysiology

CBD is the pathology underlying approximately 50% of CBS cases.

Diagnosis

The Armstrong criteria were proposed in 2013; the accuracy of these is limited and further research is needed. Symptoms may be symmetric or asymmetric, with one or more of the following:

limb rigidity or akinesia
limb dystonia
limb myoclonus, plus one of:
orobuccal or limb apraxia
cortical sensory deficit
alien limb phenomena

The onset is insidious with gradual progression, lasting one year or more, with no [|exclusion criteria] present. The diagnosis is more likely if onset is after age 50, there is no family history, and there is no genetic mutation affecting T.
Probably sporadic CBS is more likely if there are two of:

limb rigidity or akinesia
limb dystonia
limb myoclonus

plus two of:

orobuccal or limb apraxia,
cortical sensory deficit
alien limb phenomena

The diagnosis is excluded if there is evidence of:

Lewy body disease
multiple system atrophy
Alzheimer's disease
amyotrophic lateral sclerosis
semantic or logopenic variant primary progressive aphasia
structural lesion suggestive of focal cause
granulin mutation or reduced plasma progranulin levels
TDP-43 or fused in sarcoma mutations

The diagnostic criteria for clinical use may result in a misdiagnosis of other tau-based diseases.
The probable criteria are proposed for clinical research.

Differential

Other degenerative pathologies that can cause corticobasal syndrome include:

Alzheimer's disease
Pick's disease with Pick bodies
Lewy body dementias
Neurofilament inclusion body disease
Creutzfeldt–Jakob disease
Frontotemporal degeneration due to progranulin gene mutation
Motor neuron disease‐inclusion dementia.

The symptoms of classic CBS differ from CBD in that CBD also includes cognitive deficits in the executive functions.

Prognosis

The average survival time after disease onset is estimated at 6.5 years.