Oculomotor Abnormalities in Anti-Glutamic Acid Decarboxylase-Positive Stiff Person Syndrome

Background: Antibodies to glutamic acid decarboxylase (anti-GAD) can give rise to stiff person syndrome (SPS), an infrequent autoimmune condition of the central nervous system marked by fluctuating muscular rigidity and stimulus-evoked spasms. Disturbances in eye-movement control are rarely identified yet may provide insight into underlying neural involvement. Methods: Two individuals with anti-GAD-related SPS showing distinctive ocular-motor abnormalities were examined with quantitative videonystagmography, supplemented by representative video documentation. Results: Recordings demonstrated varied patterns of ocular-motor disturbance, including reduced smooth-pursuit accuracy, delayed saccadic initiation, dysmetria, intrusive saccades, and several nystagmus types. Partial improvement occurred after immunomodulatory therapy. Conclusions: These findings extend current understanding of the anti-GAD SPS phenotype and indicate that quantitative analysis of eye movements may offer a sensitive, non-invasive marker of disease activity. Larger, prospective studies are needed to clarify prevalence and responsiveness to treatment.