Hemiconvulsion–hemiplegia syndrome revisited: longitudinal MRI findings in 10 children

AIM: Hemiconvulsion-hemiplegia syndrome (HHS) is a rare severe epilepsy of infancy consisting of unilateral convulsive status epilepticus immediately followed by transient or lasting ipsilateral hemiplegia. HHS may occur either in patients with previous brain pathology or without any identified cause, so-called 'idiopathic HHS'. METHOD: We retrospectively analysed clinical and MRI longitudinal findings of a series of 10 patients (six females, four males) presenting with HHS. Age at the study inclusion ranged from 2 years 6 months to 15 years (mean of 5 y 10 mo, median 4 y 2 mo). After defining magnetic resonance imaging (MRI) features as 'typical', i.e. strictly unilateral involvement, and 'atypical', i.e. bilateral, we compared clinical data from both groups. Cognitive level was assessed using Brunet-Lézine or Wechsler scales. RESULTS: HHS occurred at a mean age of 20.5 months (range 8-48 mo). In all cases, status epilepticus lasted for more than 1 hour and was characterised by unilateral clonic seizures followed by ipsilateral hemiplegia (persistent in five patients). Two patients in this series died: the first from multi-organ failure 2 weeks after the status epilepticus and the other from a second episode of ipsilateral intractable febrile status epilepticus 3 years after the first episode. Early MRI (days 1-7 from status epilepticus) showed hemispheric cytotoxic oedema in all, extending to the contralateral side for one. T2 hyperintensity in the basal ganglia was disclosed in 70% of patients and in the hippocampus in 60%. After 1 month (in intermediate and chronic phases), all surviving patients but one showed hemispheric cortical atrophy corresponding to the regions involved during the early stage. Comparing clinical features of patients presenting with 'typical' features, to those with 'atypical' findings, the second group presented psychomotor delay before status epilepticus. INTERPRETATION: This series underlines the major value of early MRI for the prompt diagnosis of HHS, and shows that involvement of subcortical structures has been underestimated. Hippocampal involvement is not constant.