Hypertrophic olivary degeneration mimics relapse in neuromyelitis optica spectrum disorder

Abstract

A 51-year-old woman developed subacute ataxia and intractable vomiting. MRI showed left dentate and area postrema lesions (figure 1, A–C). Serum aquaporin-4–immunoglobulin G positivity confirmed neuromyelitis optica spectrum disorder. Treatment was with steroids and plasmapheresis acutely and maintenance 6-monthly rituximab. MRI 9 months later revealed a new asymptomatic right medullary lesion (figure 1, D and E), prompting mycophenolate add-on therapy. The hypertrophy, expected location, and time course led us to diagnose hypertrophic olivary degeneration from dentato-rubro-olivary circuit (Mollaret triangle [figure 2]) interruption; no palatal tremor occurred.1,2 Mycophenolate was discontinued. Failure to recognize a medullary lesion as hypertrophic olivary degeneration from a prior insult along the Mollaret triangle may lead to unnecessary treatment.