Objective: To assess the role of video-oculography (VOG) in the differential diagnosis of neurodegenerative ataxias and NP-C by evaluating saccadic velocity and smooth pursuit gain values. 

Background: Neurodegenerative ataxias are chronic progressive group of disorders which may be caused by a number of molecular etiologies. Niemann-Pick Type C (NP-C) may present with ataxia in adult age, due to its heterogeneous clinical presentation, however, its diagnosis may be difficult.  Slowing of vertical saccades, also an early and characteristic finding of the disease may help the diagnosis.

Methods: We evaluated 50 patients with idiopathic or heredodegenerative ataxia and 50 age and sex-matched healthy control subjects. Saccadic and smooth pursuit eye movements for different angles and different directions were recorded by using VOG. International Cooperative Ataxia Rating Scale was used to rate severity of ataxia in the patient group. Various parameters derived from these measurements were compared between patient and control groups using SPSS (Statistical Package for the Social Sciences).

Results: Saccadic eye movement velocity and smooth pursuit gain values in the patient group were significantly lower for all directions and all angles as compared to healthy subjects. In the patient group, 3 out of 50 were suspected to have NP-C based on the dissociation between their markedly impaired vertical saccadic velocity as compared to normal/slightly impaired horizontal saccades and relatively intact smooth pursuit movements. The diagnosis in all 3 cases was confirmed with molecular analysis, and Miglustat treatment was started.  In one of the NPC cases, where VOG evaluation was available before and after treatment, slowing in horizontal saccadic velocity was found to be within normal limits after 6 months of treatment. 

Conclusions: Our findings reveal that cerebellar pathology in degenerative ataxias is associated with impaired saccadic velocity and smooth pursuit gain. In NP-C impaired vertical saccades as opposed to relatively preserved other eye movements may be a diagnostic marker. Recording of eye movements could be useful in differential diagnosis and monitorization of treatment effects in NP-C. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/video-oculography-assessment-in-neurodegenerative-ataxias-and-neimann-pick-type-c/