Downbeat Nystagmus and Saccadic Oscillations in Spinocerebellar Ataxia Type 27B: A 14-Month Follow-Up Case Report.

Introduction: Spinocerebellar ataxia type 27B (SCA27B) is a late-onset autosomal dominant cerebellar disorder associated with oculomotor abnormalities, particularly downbeat nystagmus (DBN) and saccadic oscillations such as square-wave jerks (SWJ). Although these features are common, their longitudinal evolution and response to aminopyridine therapy remain insufficiently characterized. Case Presentation: We report a 67-year-old male with genetically confirmed SCA27B. At baseline, he presented with cerebellar ataxia (SARA score 11) and frequent SWJ, while DBN was detectable only during head-shaking. After 12 months, mild clinical progression was observed (SARA score 12) with the emergence of spontaneous DBN, which intensified during provocative maneuvers. Treatment with 4-aminopyridine (20 mg/day) resulted in clinical improvement after 2 months, reflected by a reduced SARA score (8) and improved gait, stance, and speech. However, video-oculography showed only minimal changes in DBN and no significant reduction in SWJ frequency. Conclusion: This case highlights that DBN in SCA27B may initially be detectable only under provocative conditions before becoming spontaneous. Despite clinical improvement with 4-aminopyridine, objective oculomotor parameters remained largely unchanged, suggesting a possible dissociation between clinical and oculomotor outcomes. Larger longitudinal studies are needed to clarify these relationships.