Hemiconvulsion-hemiplegia epilepsy syndrome

Hemiconvulsion-hemiplegia epilepsy syndrome (HHE) is a clinical syndrome of infancy or early childhood that is associated with seizures, cerebral hemiatrophy and transient or permanent epilepsy.

It refers to the characteristic holohemispheric global atrophy of one hemisphere, that is independent of any vascular territory and subsequently follows a causative episode of prolonged clonic seizures in the course of a febrile disease. The prolonged unilateral predominant seizure(s) in the initial episode occurs in children usually younger than 4 years of age and are referred to as hemiconvulsion-hemiplegia syndrome (HH).

Epidemiology

The exact incidence of this uncommon syndrome is unknown. Overall there has been decreasing incidence in the industrialized countries over the past decades.

Clinical presentation

Classic patient history is that of initial prolonged hemiconvulsion in infancy or early childhood in a febrile context with immediate flaccid hemiplegia (HH episode), subsequently followed by focal seizures after a seizure-free interval of months to years.

Pathology

The mechanisms underlying the syndrome are not clarified.

Several factors might contribute to the pathogenesis of HH/HHE syndrome ¹:

• prolonged seizure of long duration (possibly unnoticed) impairing metabolism of neuronal cells and leading to excitotoxic cell damage

• prolonged febrile seizure with an aggravation of cell injury by co-existent inflammation

• impairment of blood-brain-barrier permeability by both inflammatory changes and prolonged seizure

• predisposing genetic factors and/or focal epileptogenic lesion allowing for prolonged seizure

Radiographic features

CT

Late stage may demonstrate ⁶:

• slight, moderate or marked hemispheric atrophy

• focal atrophy or porencephaly

• no abnormalities at all

MR

In late stage may additionally depict ⁵:

• subcortical cavitations in the affected hemisphere

• reduced caliber of ACA, MCA or PCA on the affected side

• small corpus callosum

• ipsilateral hemispheric volume loss with a shift of midline structures

• usually lack hemosiderin on T2*/SWI

Treatment and prognosis

Prevention is better than cure and early and aggressive termination of seizures is considered the most effective way to prevent post-convulsive hemiplegia ⁹.

In the failure of conservative treatment with antiseizure medications, epilepsy surgery may be indicated ⁷.

History and etymology

It was first described by the French neurologist Henri Jean Pascal Gastaut (1915-1995) et al. in 1960 ⁴.

Differential diagnosis

For cerebral hemiatrophy include ⁸:

• congenital disorders

  • schizencephaly

  • polymicrogyria

  • Sturge-Weber syndrome

  • progressive facial hemiatrophy (Parry-Romberg syndrome)

  • hemiatrophy with multiple developmental venous anomalies

• post-traumatic changes

• infections/inflammatory changes

  • Rasmussen encephalitis

    • clinics: shorter or no symptom-free interval at all

  • unihemispheric cerebral vasculitis

• cerebral infarction

  • hypoxic ischemic encephalopathy

• hemiplegic migraine