Unidirectional Palsy of Torsional Saccades in Ataxia Associated with Anti-GAD Antibody

Antibodies against glutamic acid decarboxylase (GAD) are associated with various neurological syndromes including cerebellar ataxia and ocular motor abnormalities. We report a 67-year-old man with progressive dizziness and imbalance, who exhibited spontaneous downbeat and torsional nystagmus, normal vertical saccades, and a unilateral loss of torsional saccades during head tilting. Serum anti-GAD antibody was elevated. Tests for other autoantibodies and genes responsible for spinocerebellar ataxia were negative. Brain MRI showed cerebellar vermis atrophy The selective deficit of ipsiversive torsional saccades, with preserved vertical saccades, implicates involvement of the unilateral rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) that generates torsional and vertical saccades. This case highlights a novel ocular motor finding in anti-GAD antibody-associated ataxia and expands the spectrum of eye movement abnormalities related to midbrain and cerebellar dysfunction.