Corticobasal degeneration ( CBD ) is a neurodegenerative disorder of mid- to late- adult life. Clinically, CBD is characterized by: 1) an insidious onset and a slowly developing, assymetric, progressive, levodopa-unresponsive parkinsonian syndrome with dystonia or myoclonus; 2) cortial features, such an apraxia, alien limb phenomenon and cortical sensory loss. Definitive clinical diagnostic criteria are not available so that a neuropathological examination remains essential for accurate diagnosis of CBD. Consequently, there is a need for the identification of additional criteria in life.
Electrophysiological examination provides information about the functionality of a number of cortical and subcortical brain structures involved by CBD. The disorder features a specific cortical (fronto-parietal) abnormality that could help differentiate CBD from a number of other extrapyramidal syndromes. Examination of myoclonus in CBD reveals short latency cortical C-responses. However, other typical cortical myoclonic features are missing eg giant somataesthetic evoked potentials and cortical potentials preceding myoclonus in jerk- locked back-averaged recordings. Some authors interpret these abnormalities as signifying a subcortical origin of the myoclonus. The CBD-associated fronto-parietal abnormality has also been explored in studies of ocular movements. Asymmetric lengthening of the lateral ocular saccade latency is more in favour of CBD than of progressive supranuclear palsy.
Cognitive functions are also compromised early in CBD although this feature does not readily distinguish CBD from PSP or from fronto-parietal dementia. Studies of cognitive potentials may confirm subcortico-frontal abnormalities and thus dissociate CBD from PSP associated patterns. Other electrophysiological tests (examination for dysautonomia, the palmo-mental reflex, the blink reflex) give results that overlap those from other extrapyramidal syndromes ; polysomnography recordings resemble those of the synucleopathies, prompting hypotheses about the pathophysiological mechanisms underlying these various diseases.
© 2007 Elsevier Masson SAS. Tous droits réservés.