A 5-year-old boy with a history of West syndrome (infantile spasms) at 7 months of age now presents with multiple seizure types including tonic seizures during sleep, atonic seizures (drop attacks), and atypical absence seizures. He has severe intellectual disability and has failed multiple antiepileptic drugs. EEG shows a slow disorganized background with characteristic generalized discharges marked as **A** in the diagram, occurring in prolonged runs at 1.5–2.5 Hz, with paroxysmal fast activity during sleep. Which of the following best describes the clinical significance of the EEG pattern marked **A** in establishing the diagnosis?
A. It is the pathognomonic EEG hallmark of Lennox-Gastaut syndrome, representing an epileptic encephalopathy with multiple drug-resistant seizure types and cognitive impairment
B. It is the photoparoxysmal response pattern seen in juvenile myoclonic epilepsy, which is best managed with valproate and has a favorable long-term prognosis
C. It is the hypsarrhythmic pattern of West syndrome, which typically resolves by age 3–5 years with ACTH or vigabatrin treatment
D. It is the characteristic 3 Hz spike-and-wave pattern seen in childhood absence epilepsy, which responds well to ethosuximide monotherapy
Explanation
Why Option 1 is correct
The EEG pattern marked A — slow generalized spike-and-wave discharges at 1.5–2.5 Hz occurring in prolonged runs, with paroxysmal fast activity during sleep — is the pathognomonic EEG hallmark of Lennox-Gastaut syndrome (LGS). This pattern, combined with the clinical triad of multiple drug-resistant seizure types (tonic, atonic, atypical absence), severe cognitive impairment, and evolution from West syndrome, establishes the diagnosis of LGS as an epileptic encephalopathy of childhood. Per Nelson Textbook of Pediatrics, the slow spike-wave pattern at 1.5–2.5 Hz (slower than the 3 Hz of typical absence) is the defining EEG feature that distinguishes LGS from other childhood epilepsies.
Why each distractor is wrong
Option 2: The 3 Hz spike-and-wave pattern (marked C in the diagram) is characteristic of childhood absence epilepsy, not LGS. Absence seizures are brief, have good prognosis, and respond well to ethosuximide — none of which apply to this patient with drug-resistant LGS and severe disability.
Option 3: Hypsarrhythmia (marked B in the diagram) is the chaotic, high-amplitude background seen in West syndrome with infantile spasms. Although this patient had West syndrome at 7 months, the EEG pattern evolved to the slow spike-wave of LGS by age 3–5 years; hypsarrhythmia does not persist and does not explain the current clinical picture.
Option 4: The photoparoxysmal response (marked D in the diagram) is seen in juvenile myoclonic epilepsy, characterized by myoclonic jerks on awakening and generalized tonic-clonic seizures. This patient has tonic, atonic, and atypical absence seizures with no myoclonic component, and JME has a much better prognosis than LGS.
High-YieldNEET PG
Lennox-Gastaut syndrome is defined by the triad of slow (1.5–2.5 Hz) spike-and-wave EEG, multiple drug-resistant seizure types, and cognitive impairment; it evolves from West syndrome in 30–50% of cases and carries a poor prognosis.
Nelson Textbook of Pediatrics, 21st ed., Chapter 611: Lennox-Gastaut Syndrome
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