corticobasal degeneration

Definition: Corticobasal degeneration (CBD) is a sporadic neurodegenerative Parkinson-like movement disorder. Corticobasal degeneration is part of the FTD spectrum of disorders.

This is a disease of the elderly, with considerable clinical and neuropathologic heterogeneity. The extrapyramidal signs and symptoms result in this disorder’s also being grouped with syndromes of basal ganglia dysfunction.

Clinical synopsis

The disease is characterized by extrapyramidal rigidity, asymmetric motor disturbances (jerking movements of limbs: "alien hand"), and sensory cortical dysfunction (apraxias, disorders of language); cognitive decline occurs, and may be prominent in some cases.

The same extended tau haplotype is linked to CBD as to PSP. Although tau deposits are a hallmark of CBD, it is rare to find CBD pathology in individuals with mutations in the tau gene.

It has many clinical overlapping features with progressive supranuclear palsy (PSP). The major difference with PSP is a marked asymmetry of the symptoms at onset.

Corticobasal degeneration is further characterized by impaired balance and abnormal muscle postures of the limb (dystonia). Frontotemporal dementia (FTD)-like dementia is also often observed later in the disease course.

Morphology

On macroscopic examination, there is cortical atrophy, mainly of the motor, premotor, and anterior parietal lobes. The regions of cortex show severe loss of neurons, gliosis, and "ballooned" neurons (neuronal achromasia) that can be highlighted with immunocytochemical methods for phosphorylated neurofilaments.

Tau immunoreactivity has been found in astrocytes ("tufted astrocytes"), oligodendrocytes ("coiled bodies"), basal ganglionic neurons, and, variably, cortical neurons.

Clusters of tau-positive processes around an astrocyte ("astrocytic plaques") and the presence of tau-positive threads in gray and white matter may be the most specific pathologic findings of CBD. The substantia nigra and locus ceruleus show loss of pigmented neurons, neuronal achromasia, and tangles.

Similar to PSP, the tau deposits in CBD contain predominantly 4 repeat tau. Recently proposed consensus diagnostic criteria for CBD focus on the presence of tau-positive inclusions in neurons and glia of the cortex and striatum, including astrocytic plaques, associated with neuronal loss from substantia nigra and cortex.

Physiopathology

Abundant tau pathology in the form of fine filaments (NFTs) characterizes CBD neuropathologically.
See also

 neurodegenerative diseases