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

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.

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.

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.