[Contribution of oculomotor examination for the etiological diagnosis of parkinsonian syndromes].

Exploration of ocular motricity can be helpful for diagnosis in certain parkinsonian syndromes. Oculomotricity is perturbed in Parkinson's disease (PD) and in multiple system atrophy (MSA). The minimal anomalies, sometimes observed in these conditions, both clinically and on oculomotor recordings, cannot contribute significantly to diagnosis. In corticobasal degeneration (CBD), infraclinical oculomotor anomalies can be identified on oculomotor recordings and are relatively specific to atypical parkinsonian syndrome: particularly long latency of ocular saccades related to posterior parietal involvement. The most significant contribution is observed for progressive supanuclear palsy (PSP) where the oculomotor anomalies are evident at clinical examination and are even the cardinal signs of the condition: particularly paralysis of vertical ocular saccades (downbeat and upbeat) or downbeat saccades, ocular pursuit also being perturbed but not reflex movements (preservation of oculocephalic reflexes). This dissociation between palsy of saccade and pursuit movements and preservation of oculocephalic reflexes is the sign of the supranuclear origin of the oculomotor disorder in PSP. In early stage PSP before clinical expression, requiring oculomotor recordings to be recognized, it is relatively specific in the context of degenerative parkinsonian degeneration. PSP also involves other less specific anomalies such as a perturbation of the antisaccade movements (related to a frontal syndrome), anomalous ocular pursuit (becoming saccadic) and presence of square wave. A rigorous clinical examination of oculomotor function at a more advanced stage of PSP, or oculomotor recordings at an early stage of PSP or CBD, can thus contribute significantly to the diagnosis of both conditions.