Neuromyelitis optica presenting with mammillary body and cervicomedullary lesions after severe hyponatremia mimicking osmotic demyelination syndrome.

Neuromyelitis optica spectrum disorder is an autoimmune demyelinating disease that usually targets the spinal cord and optic nerves, though occasionally other central nervous system structures are involved. There are variants of neuromyelitis optica spectrum disorder that can mimic metabolic or osmotic demyelinating diseases on imaging. A 54-year-old female with a history of hypertension and Roux-en-Y bypass presented with numbness, weakness, dizziness, and blurred vision and concurrent severe hyponatremia (serum sodium 115 mmol/L). She was admitted and treated for monitored correction of her symptomatic hyponatremia and was discharged after stabilization. Weeks following discharge, she had onset of new neurological symptoms and brain magnetic resonance imaging revealed increased fluid-attenuated inversion recovery signal in the bilateral mammillary bodies and dorsal columns of the upper cervical spinal cord, patchy enhancement at the cervicomedullary junction, and a lesion at C2-C3. Cerebrospinal fluid studies were unremarkable. While osmotic demyelination was suspected initially based on the history of profound hyponatremia and distribution of lesions, further neurologic assessment confirmed neuromyelitis optica spectrum disorder. To our knowledge, only 1 other case of mammillary body involvement in AQP4-positive neuromyelitis optica spectrum disorder presenting in the setting of severe hyponatremia and with close radiographic resemblance to osmotic demyelination syndrome has been reported. In summary, our case demonstrates radiographic mimicry of osmotic demyelination syndrome by neuromyelitis optica spectrum disorder. Consideration of neuromyelitis optica spectrum disorder should be maintained on the differential diagnosis of patients with mammillary body and cervicomedullary lesions following hyponatremia, especially with regard to the presence of enhancement and progression of lesions.