A 53-year-old woman presented with ataxia, dysarthria, and vertical binocular diplopia on left and right gaze but absent in primary gaze. Her symptoms were progressive over several months without clear inciting event. Initial neuro-ophthalmology evaluation showed subtle downbeat nystagmus in primary gaze that increased in horizontal gaze, consistent with “side-pocket” phenomenon.1 On cross-cover testing, she was found to have an alternating skew deviation (ASD), raising question of cerebellar localization (Video 1). Multiple etiologies can lead to ASD including autoimmune, ischemic, and paraneoplastic entities. Prior structural imaging was unrevealing. Serum studies revealed elevated glutamic acid decarboxylase antibody (anti-GAD65) levels (>250.0 IU/mL, normal range 0–5.0 IU/mL). She was subsequently diagnosed with anti-GAD65 cerebellitis. The patient was not screened for a neoplasm because anti-GAD65 is rarely paraneoplastic in nature. Anti-GAD65 interferes with the production of GABA, thereby disrupting supranuclear pathways and has been associated with autoimmune epilepsy and stiff-person syndrome. Intravenous immunoglobulin may improve outcome.2
C. Bell: drafting/revision of the manuscript for content, including medical writing for content. P. Drummond: major role in the acquisition of data. S. Grossman: drafting/revision of the manuscript for content, including medical writing for content; study concept or design; analysis or interpretation of data.
The authors report no targeted funding.
The authors report no disclosures relevant to the manuscript. Go to Neurology.org/N for full disclosures.
Go to Neurology.org/N for full disclosures.
Submitted and externally peer reviewed. The handling editor was Resident and Fellow Section Editor Whitley Aamodt, MD, MPH.
Teaching slides links.lww.com/WNL/C558
- Received August 19, 2022.
- Accepted in final form November 15, 2022.
- © 2022 American Academy of Neurology