Objective: To study ocular movements (ocular pursuit, nystagmus and saccades) in the most frequent ataxias (SCA2, SCA3 and Friedreich’s ataxia), to find out which variables allow to discriminate between the different hereditary ataxias.

Background: Degenerative ataxias are a heterogeneous group of entities represented by a great majority of spino-cerebellar ataxias (SCAs), especially of types 2,3,7,10 and 17 in our environment, as well as the most frequent of the recessive ones, Friedreich’s ataxia (FA). In general, patients present a cerebellar syndrome accompanied by oculomotor disorders, among other manifestations. Our interest was to find the type of oculomotor alteration that characterizes each entity. The approach to this investigation was made through oto-neurophysiological tests.

Method: We studied 25 patients with molecular diagnosis of SCA2, SCA3 and FA, who gave their informed consent to be submitted to the oto-neurophysiological tests of the protocol. Descriptive exploration of the 3 groups was carried out before a multivariate analysis, taking the diagnosis as dependent variable. A set of independent neurophysiological variables was composed by ocular pursuit, the speed of saccades, the presence of saccadic intrusions, anti-saccades, optokinetic nystagmus, spontaneous nystagmus, oculo-vestibular reflex and caloric tests among others.

Results: We studied 25 subjects, 13 men and 12 women ( 11 with SCA2, 8 with SCA3 and 6 with FA). The average age of onset was 24.5 years, being significantly younger in patients with Friedreich ataxia. Six of nine variables showed a highly significant difference in one of the three entities (saccades velocity, saccadic intrusions, antisaccades, VOR). The speed of ocular pursuit is altered in SCA2 (p = 0.001) as well the anti-saccade test(p <0.001). The presence of saccadic intrusions is as a characteristic of Friedreich's Ataxia (p <0.001). We found that the horizontal optokinetic reflex is more affected in SCA3 (p = 0.016).The oculovestibular reflex (VOR) cannot be performed in SCA2 due to a gegenhalten cervical phenomenon (p = 0.009). Finally the caloric tests are normal in AF while they show only drift in SCA2 and the greater affectation in SCA3 (p = 0.004)

Conclusion: Two third of the oto-neurophysiological variables where significantly affected in one of the three entities. The study of these aspects of eye movements could guide the clinical diagnosis before the molecular confirmation.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/study-of-eye-movements-as-a-tool-in-the-diagnosis-hereditary-ataxias/