Anti-DPPX Autoimmune Encephalitis

A 52-year-old man presents with 4 months of progressive cognitive decline, prominent diarrhea with 8 kg weight loss, insomnia, hyperstartle, myoclonus, and new-onset focal motor seizures with secondary generalization. MRI brain is normal. Video-EEG demonstrates diffuse theta-delta background slowing, generalized rhythmic delta activity, and multifocal sharp waves. The abnormality marked **B** in the diagram is noted during captured focal seizures with facial clonus and versive head turning. Serum and CSF autoimmune encephalitis panel detects high-titer antibodies against DPPX (dipeptidyl-peptidase-like protein 6), a regulatory subunit of the Kv4.2 potassium channel. Which of the following best explains the clinical and electrographic findings in this patient?