Lennox-Gastaut Syndrome

A 5-year-old boy with a history of infantile spasms at 6 months (treated with ACTH and vigabatrin) presents with multiple daily seizure types including drop attacks, brief tonic seizures during sleep, and atypical absence seizures. He has moderate intellectual disability and wears a protective helmet due to repeated falls. His awake EEG shows the pattern marked **A** in the diagram—diffuse slow spike-and-wave discharges at 1.5–2.5 Hz that are asymmetric and irregular, arising from a disorganized background. Which of the following best distinguishes this EEG pattern from childhood absence epilepsy?

A 5-year-old boy with developmental delay presents with multiple daily seizures including drop attacks and tonic seizures during sleep. His EEG shows the pattern marked **B** in the diagram. Which of the following is the most likely diagnosis, and what is the primary reason this EEG finding is pathognomonic for this condition?