Ocular motor abnormalities in Parkinsonian syndromes: a review

Introduction: Oculomotor abnormalities can be observed in all Parkinsonian syndromes. Besides the eponymous vertical gaze palsy in Progressive Supranuclear Palsy (PSP), oculomotor alterations are generally not considered to contribute substantially to the differenzial diagnosis of Parkinsonian syndromes.

Material and Methods: There are subtle differences of apparently similar oculomotor alterations in Parkinson's disease (PD) and atypical neurodegenerative Parkinsonian syndromes (Multiple System Atrophy (MSA), Progressive Supranuclear Palsy) that can contribute to the early differenzial diagnosis of these entities. Additionally we evaluate the major recording techniques for eye movements.

Results: The underlying pathomechanisms of oculomotor dysfunction in PSP and MSA seem to be closely related to the major neuropathological changes of these diseases with alterations of burst- and omnipause neurons in the midbrain in PSP and OPCD in MSA, respectively. In PD, the situation appears to be more challenging. There is no doubt that PD-associated dopaminergic depletion with loss of dopaminergic input to the striatum will lead to the disruption of a prefrontal-basal ganglial circuitry that is crucial to some aspects of oculomotor function. However, the high interindividual variability of oculomotor symptoms in PD, its only loose correlation to the severity of major dopaminergic deficits (i.e., motor symptoms), the heterogenous reports about the effect of dopaminergic medication on oculomotor function, and growing evidence for a possibly non-dopaminergic influence of frontal lobe pathology remain not fully understood and need further investigation.

Conclusion: By use of a thorough investigation of oculomotor function via spezialized recording techniques (e.g. videooculography), it is possible to elicit different causalities of apparently similar oculomotor deficits within the group of Parkinsonian syndromes that may help in the distinction of these entities. In conclusion, the most challenging aspect for the clinician in the differenzial diagnosis of Parkinsonian syndromes is probably the differentiation of PD from atypical Parkinsonian syndromes such as PSP-P in the early course of disease. Although most Parkinsonian syndromes share a number of oculomotor deficits, careful investigation beyond bedside examination potentially unravels unique features of oculomotor dysfunction in PD, MSA and PSP.