Corticobasal degeneration, a 4R tauopathy

Corticobasal degeneration (CBD) is a slowly progressive neurodegenerative disorder characterized by an asymmetrical akinetic-rigid syndrome associated with cognitive (apraxia and aphasia) and extrapyramidal motor dysfunction (rigidity and dystonia). Moderate dementia emerges sometimes late in the course of the disease (Rinne et al., 1994).

Neuropathological examination shows gliosis, neuronal loss, presence of achromatic ballooned neurons, neuritic changes and neurofibrillary tangles (Paulus et al., 1990 ; Ksiezak-Reding et al., 1994; Feany et al., 1994; Buée-Scherrer et al., 1996b) and astrocytic plaques.

There is an overlap between progressive supranuclear palsy (PSP) and CBD (Feany et al., 1996), and it would be most helpful to distinguish these two pathologies on a neuropathological or immunochemical basis.

By comparison, CBD is less prevalent, and usually dysplays a more severe cortical atrophy with fronto-parietal predominance partly sparing the central area.

Neuropathology: Cytoskeletal pathology is complex, in that it combines conspicuous chromatolytic neurons in large numbers without argentophilic inclusions. Cortico glio-fibrillar plaques have also been described, as well as aberrant neurites in the white matter. The degenerative pathology of the basal ganglia and rhombencephalon is not as sharply targeted on specific nuclei as in PSP, and also involves a striking number of chromatolytic neurons. Astrocytic laques are large with a hollow center, while those from PSP are stained with anti-tau in their center, (tuffed plaques).

At the biochemical level, the profile of neurofibrillary tangles is similar to PSP, as well as the Tau electrophoretic profile (Ksiezak-Reding et al., 1994 ; Feany et al., 1995a ; Buée-Scherrer et al., 1996b).

Tau lesions in PSP and CBD are exclusively composed of tau isoforms with exon 10 (Sergeant et al, 1999). This is a 4R tauopathy.

The upper tau doublet, so characteristic, is found in subcortical and cortical areas at the last stage of the disease, when dementia is observed.

At the biochemical level, we were not able to distinguish between PSP and CBD: are they at th opposite ends of the same spectrum?