By: Catherine Joachin

Hemiconvulsion-Hemiplegic Epilepsy

Introduction

Hemiconvulsion-hemiplegia epilepsy (HHE) is a rare consequence of prolonged focal status epilepticus in infancy and early childhood (Auvin et al. 2012). It involves sudden unilateral focal motor convulsions, followed by ipsilateral hemiplegia and epilepsy, in that order.

Symptomatology

Acute rhythmic body shaking primarily affects only one side of the body, hence the term hemiconvulsion. This is immediately accompanied by a complete loss of strength or paralysis on the same side as the convulsion (hemiplegia), and later, chronic focal drug-resistant seizures (epilepsy) (Albakaye et al., 2018; Auvin et al. 2012). Hemiplegia is usually permanent, but may disappear in around 20% of cases whereas seizures are most often simple partial seizures (33%), partial seizures with secondary generalization (20%) and repeated episodes of status epilepticus (10%) (Bhat, Kakkar & Prokashini, 2014). Most HHE patients also have severe intellectual disability (Auvin et al. 2012).

This condition primarily affects children younger than 4 years of age, with onset commonly occurring between 5 months and 2 years of age (Bhat, Kakkar & Prokashini, 2014).

Diagnosis

Diagnosis is facilitated by observing clinical course and disease-specific neuroimaging features. HHE follows a chronological course, therefore a diagnosis should be taken into consideration when persistent hemiplegia is observed after a long febrile convulsive seizure in a young child (Auvin et al. 2012).

Neuroimaging studies have revealed acute unilateral edema in the affected brain hemisphere, with swelling often progresses into cerebral hemiatrophy (volume loss) in the following weeks (Albakaye et al., 2018). During the acute phase, edema can be severe enough to result in life-threatening temporal lobe herniation, in which shifting of brain tissue can exert intracranial pressure on the skull (Auvin et al. 2012).

Although EEG recordings can be used to rule out ongoing status epilepticus, a diagnosis of HHE does not require an EEG (Auvin et al. 2012). Compared to recordings from the unaffected brain hemisphere, which typically shows slow waves with reappearing physiological rhythms, EEG recordings from the affected hemisphere shows higher amplitude delta slowing, sometimes paired with a short period of suppression activity (Auvin et al. 2012).

Treatment

HHE is a relatively unknown and poorly understood condition, which explains the scarcity of available neuropathological data and uncertainty surrounding its etiology.

Although there is no cure for HHE, standard treatment involves medical therapy for seizure control. Frontline pharmacological options include carbamazepine, phenytoin, valproate and lamotrigine (Albakaye et al., 2018). Surgical treatment has also been found to be successful in medically resistant cases (Auvin et al. 2012).

Conclusion

Hemiconvulsion-hemiplegia epilepsy is an uncommon pediatric epilepsy syndrome marked by sequential focal febrile convulsive seizures, hemiplegia and chronic epilepsy affecting only one side of the body. HHE diagnosis is informed by knowledge of chronological nature of the condition and EEG recordings of characteristic slow delta brain waves on the epileptic hemisphere. Treatment is currently centred on the use of medical therapy to control seizures, but no definitive cure has been found. Further research is imperative to uncover the pathophysiological mechanisms underlying this syndrome, as it remains an unclear, but severe public health issue.

References

Albakaye, M., Belaïdi, H., Lahjouji, F., Errguig, L., Kuate, C., Maiga, Y., Diallo, S. H., Kissani, N., & Ouazzani, R. (2018). Clinical aspects, neuroimaging, and electroencephalography of 35 cases of hemiconvulsion-hemiplegia syndrome. Epilepsy & Behavior, 80, 184–190. https://doi.org/10.1016/j.yebeh.2017.12.018

Auvin, S., Bellavoine, V., Merdariu, D., Delanoë, C., Elmaleh-Bergés, M., Gressens, P., & Boespflug-Tanguy, O. (2012). Hemiconvulsion–hemiplegia–epilepsy syndrome: Current understandings. European Journal of Paediatric Neurology, 16(5), 413–421. https://doi.org/10.1016/j.ejpn.2012.01.007

Bhat, R. Y., Kakkar, S., & Prakashini, K. (2014). Hemiconvulsion-hemiplegia-epilepsy syndrome: clinical course and neuroradiological features in a 20-month-old girl. BMJ Case Reports, 2014, bcr2013203482. https://doi.org/10.1136/bcr-2013-203482