An immune attack by anti–glutamic acid decarboxylase (GAD) antibodies is believed to cause a deficiency in gamma-aminobutyric acid–mediated neurotransmission in the cerebellum. This, in turn, leads to several eye movement disorders, including spontaneous downbeat (DBN) and periodic alternating nystagmus. We describe a 68-year-old diabetic woman with disabling paroxysmal positioning upbeat nystagmus (UBN) exclusively in the supine position, associated with asymptomatic spontaneous DBN, alternating skew deviation and hyperactive vestibulo-ocular reflex responses on head impulse testing, in whom high titers of anti-GAD antibodies were detected. After treatment with intravenous immunoglobulin, a complete resolution of positioning UBN and spontaneous DBN occurred, along with a decrease in anti-GAD antibody titers. Positioning UBN in this case may reflect a transient disinhibition of the central vestibular pathways carrying posterior semicircular canal signals, due to lack of normal inhibitory input from the cerebellar nodulus/uvula. Immunoglobulin restored cerebellar inhibitory output, possibly by improving gamma-aminobutyric acid neurotransmission.
Address correspondence to João Lemos, MD, Department of Neurology, Coimbra University Hospital Centre, Praceta Professor Mota Pinto, 3000-075 Coimbra, Portugal; E-mail: email@example.com
The authors report no conflicts of interest.
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A. I. Martins and J. Lemos contributed equally to this article.
© 2018 by North American Neuro-Ophthalmology Society