Linking Downbeat Nystagmus and Aquaporin-4-Positive Neuromyelitis Optica: A Closer Look at Their Hidden Relationship

Neuromyelitis optica (NMO), an autoimmune disease, typically presents with loss of vision and myelopathic signs. NMO may be associated with antibodies selective for aquaporin-4 (AQP4), a water channel located within the optic nerves and spinal cord.AQP4 is distributed in the periventricular region, corpus callosum, magnocellular nuclei of the hypothalamus, and brain stem.Downbeat nystagmus (DBN) is associated with structural, metabolic, and autoimmune disorders, but is rarely reported in NMO.We treated a 33-year-old female with known AQP4-positive NMO who presented with new-onset DBN. We review the literature and discuss possible mechanisms and lesion locations hypothetically responsible for the symptoms and signs.