A 68-year-old retired schoolteacher presents with a 4-month history of rapidly progressive cognitive decline, myoclonus, visual disturbances, and cerebellar ataxia. MRI brain shows cortical ribboning and bilateral caudate-putamen involvement. CSF analysis reveals elevated 14-3-3 protein and tau >1200 pg/mL, with positive RT-QuIC assay. An EEG is performed showing the pattern marked **B** in the diagram. Which of the following clinical diagnoses is most strongly supported by this EEG finding in conjunction with the clinical and CSF profile?