• Ana I Martins, João N Carvalho, Ana M Amorim, Argemiro Geraldo, Eric Eggenberger, and João Lemos.
• Departments of Neurology (AIM, JNC, AG, JL) and Otorhinolaryngology (AMA), Coimbra University Hospital Centre, Coimbra, Portugal; and Department of Neurology and Ophthalmology (EE), Michigan State University, East Lansing, Michigan.
• J Neuroophthalmol. 2018 Mar 1; 38 (1): 32-35.

AbstractAn 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.

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