A 3-year-old boy presents with a 45-minute right-sided hemiclonic seizure during a febrile illness. Post-ictal examination reveals left-sided flaccid hemiplegia that persists beyond the acute phase. EEG performed 24 hours later shows the pattern marked **A** in the diagram. Which of the following clinical syndromes best explains this constellation of findings?

Explanation

## Why Hemiconvulsion-Hemiplegia-Epilepsy (HHE) Syndrome is right HHE syndrome (Gastaut syndrome) is defined by the classic triad: prolonged febrile hemiclonic seizure (>30 minutes), acute contralateral hemiplegia persisting beyond the seizure, and delayed focal epilepsy. The EEG finding of right-sided lateralised periodic discharges (LPDs) at 1–2 Hz with sharp morphology over the affected hemisphere is pathognomonic for the acute phase of HHE. The underlying pathophysiology involves cytotoxic edema and ischemic injury during prolonged unilateral seizures, leading to hemispheric atrophy on chronic imaging. This syndrome occurs almost exclusively in children under 4 years of age and carries a poor prognosis with drug-resistant epilepsy in 80% of cases (Nelson Textbook of Pediatrics, 21st ed., Ch. 611). ## Why each distractor is wrong - **Dravet Syndrome**: Presents with prolonged febrile seizures starting before 12 months, but the EEG shows generalized polyspike-and-wave or multifocal discharges, NOT unilateral LPDs. Dravet does not produce acute hemiplegia or unilateral hemispheric injury. - **Landau-Kleffner Syndrome**: Characterized by acquired aphasia and continuous spike-and-wave discharges during sleep (CSWS pattern), typically affecting children aged 3–7 years. It does not present with acute hemiplegia or febrile status epilepticus, and EEG shows bilateral temporal or central discharges, not lateralised periodic discharges. - **Continuous Spike-and-Wave during Sleep (CSWS)**: Defined by near-continuous spike-and-wave activity during non-REM sleep and focal seizures. It does not follow prolonged febrile hemiconvulsive status, does not produce acute hemiplegia, and lacks the characteristic LPD pattern of HHE. **High-Yield:** HHE = prolonged febrile hemiclonic seizure → acute contralateral hemiplegia → LPDs on EEG + unilateral hemispheric atrophy on MRI. [cite: Nelson Textbook of Pediatrics, 21st ed., Ch. 611; Roger's Epileptic Syndromes in Infancy, Childhood and Adolescence, 6th ed.]