CSWS / Landau-Kleffner Spectrum

A 5-year-old previously normal boy presents with progressive cognitive decline, behavioral deterioration with autistic features, and occasional focal seizures over 3 months. His parents report he was learning normally until recently. Sleep-deprived EEG shows the pattern marked **C** in the diagram—continuous bilateral synchronous spike-and-wave discharges occupying >85% of non-REM sleep, while the waking EEG shows only scattered centrotemporal spikes. Brain MRI is normal. Which of the following is the MOST APPROPRIATE first-line treatment for this condition?