A 43-year-old software engineer with no prior neurologic history presented with a new-onset tonic-clonic seizure and was incidentally found to have a cavernoma. Within weeks, he developed speech arrest, cognitive decline (MoCA 21/30), personality changes, insomnia, and diffuse myoclonic jerks (prominent in the face and upper extremities). MRI brain revealed T2/FLAIR hyperintensity in the caudate and putamen (L>R). EEG captured no correlate for the jerks. CSF analysis showed WBC 1, protein 59; autoimmune and prion panels were sent. The patient’s rapid decline, myoclonus, right leg spasticity, and basal ganglia signal abnormalities satisfied “probable CJD” criteria.  

Empiric treatment with high-dose steroids and IVIG yielded no immediate improvement. Repeat imaging demonstrated multifocal cortical and bilateral basal ganglia FLAIR hyperintensities; reviewing repeat vEEG revealed that the observed myoclonic jerks clinically resembled faciobrachial dystonic seizures (FBDS). He was discharged to rehabilitation on a prednisone taper with neuroimmunology follow-up. Post-discharge, CSF returned positive for LGI1 antibodies and negative for RT-QuIC/14-3-3, confirming LGI1 encephalitis. He is currently awaiting rituximab initiation.