Patient 1 was a 39-year-old woman with an unremarkable medical history who developed acute involuntary right arm and leg movements. Neurologic examination revealed moderate dysarthria and subcontinuous, choreic movements in her right limbs, prevailing in the arm, which worsened during postural tasks. She occasionally had ballistic movements in her right limbs and abnormal dystonic postures. Continuous peribuccal and tongue involuntary movements were noted. Moreover, bilateral upper limb ataxia, gait and trunk ataxia, and brisk right tendon reflexes were found. There was no strength or sensory loss (video 1 at Neurology.org/cp). Brain MRI revealed a tumefactive, T2/fluid-attenuated inversion recovery (FLAIR) hyperintense, T1 hypointense contrast-enhancing demyelinating lesion in the left cerebral peduncle, extending to the substantia nigra and subthalamic nucleus (STN) (figure, A-C). Multiple hyperintense T2/FLAIR, T1 hypointense, non-contrast-enhancing demyelinating lesions in the hemispheric and periventricular deep white matter, brainstem, and cerebellar hemispheres were also found. All serologic tests were within normal limits. Isoelectric focusing (IEF) revealed 9 CSF oligoclonal bands (OCBs). A diagnosis of multiple sclerosis (MS) was made and the patient was treated with high-dose methylprednisolone with improvement of symptoms.