Biphasic paraneoplastic brainstem encephalitis associated with anti-Ri antibody.

Brainstem encephalitis is not a classic paraneoplastic syndrome and usually involves monophasic neurological deterioration and has negative magnetic resonance imaging (MRI) findings. We describe a patient with brainstem encephalitis who had elevated anti-Ri antibody levels and double-step neurological deterioration associated with different abnormal lesions on MRI. Immunosuppression with steroids and intravenous immune globulin combined with aggressive treatment of the tumor successfully led to the resolution of brainstem symptoms and MRI lesions. In patients with unusual signs and symptoms of paraneoplastic encephalitis mimicking multiple sclerosis, onconeural antibody studies are recommended.