A rare saccade velocity profile in Stiff-Person Syndrome with cerebellar degeneration

Stiff-Person Syndrome (SPS) is an immune-mediated disorder of the central nervous system characterized by muscle rigidity, episodic muscle spasms, and high titers of antibodies against glutamic acid decarboxylase (GAD). The presence of cerebellar ataxia in SPS is extremely rare, but occurs. Clinical observations of ocular motor abnormalities have been noted in a few SPS patients. The purpose of this study is to provide a detailed quantitative documentation of ocular motor abnormalities in a patient with SPS and progressive cerebellar signs. Detailed clinical assessment of a woman with SPS and precise eye movement recordings using the magnetic search coil technique was performed. In addition to other ocular motor abnormalities that included longer latencies for saccades, downbeat nystagmus, and loss of downward smooth pursuit, a rare saccade velocity profile consisting of multi-component saccades was observed. We postulate that these ocular motor findings are related to impairment of GABAergic neurotransmission because antibodies to glutamic acid decarboxylase (GAD-Abs) have been implicated in the pathogenesis of both SPS and some cases of cerebellar ataxia. In addition, this unusual saccadic velocity profile may have important implications for modeling the saccadic system and furthering a complete understanding of saccade generation.