Spinocerebellar Degeneration (SCD)

Abstract

Spinocerebellar degeneration (SCD) is a group of neurodegenerative disorders characterized by progressive cerebellar ataxia with or without symptoms/signs of pyramidal, ex-trapyramidal, or peripheral nerve involvement. Patients frequently exhibit unsteadiness of gait associated with nystagmus, which could also be observed in patients with peripheral vestibular impairment. Thus, some of these patients often initially seek consultation with an otolaryngologist. To distinguish SCD from other peripheral vestibular disorders, it is necessary for otolaryngologists to understand the characteristics of SCD. Brainstem and cerebellar lesions affect physiological eye movements, so that the patients often present with various eye movement abnormalities. Slow saccades, saccade dysmetria, down-beat nystagmus, and impairment of smooth pursuit are some of the typically observed abnormalities. Reduced bilateral VOR has been observed in MJD/SCA 3 patients, especially developed more those with a disease duration of longer than six years. SCA 6 patients, considered as showing pure cerebellar ataxia, show dissociation between control of gaze tracking during smooth pursuit and VOR cancellation. This result indicates that the cerebellar Purkinje cells are not involved in the non-pursuit VOR cancellation system. Therefore, it is important for otorhinolaryngologists to be alert to typical eye movement impairments.