Epilepsy & Seizures
Generalized onset tonic seizures
Nov. 08, 2022
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Hemiconvulsion-hemiplegia-epilepsy syndrome is an exceptional dramatic sequence of a sudden and prolonged unilateral clonic seizure (hemiconvulsion, focal clonic status epilepticus) followed by permanent ipsilateral hemiplegia, which is followed by the development of severe chronic epileptic seizures after 1 to 3 years from the initial episode. Approximately 85% of children with focal clonic status epilepticus develop epilepsy within 3 years (11). Peak age of occurrence is in the first 2 years of life, with a range of 5 months to 4 years. The event occurs suddenly in an otherwise normal child, often during a febrile illness of CNS infection. The initial flaccid hemiplegia later becomes spastic; it is permanent and often very severe. Learning difficulties are probably the rule. Acute and immediate treatment of the hemiconvulsion status epilepticus is mandatory.
• Hemiconvulsion-hemiplegia-epilepsy syndrome is a disorder associated with a specific clinical presentation sequence: initial prolonged hemiconvulsion (at less than 2 years of age) and immediate flaccid hemiplegia (a hemiconvulsion-hemiplegia episode), and subsequent (after 1 to 3 years) development of focal epilepsy.
• The focal partial epilepsy may be temporal, extratemporal, or multifocal.
• Onset is associated with the presence of prolonged seizures often in a febrile context. Early administration of a benzodiazepine to reduce the duration of the initial event is of primary importance.
• Although the syndrome may be associated with prior infection or lesion in some cases, a possible cause is often not revealed.
• Therapy for hemiconvulsion-hemiplegia-epilepsy syndrome includes antiseizure medications and surgery.
The term "hemiconvulsion-hemiplegia syndrome" was first used by Gastaut (25; 24) to describe the following sequential combination: unilateral or predominantly unilateral clonic seizures (usually of long duration), occurring during the first 2 years of life and immediately followed by a flaccid hemiplegia (usually permanent), ipsilateral to the clonic seizure.
The term "hemiconvulsion-hemiplegia-epilepsy syndrome" was used to describe the complete form of the syndrome. It included the consequent development of a focal onset epilepsy, usually occurring after 1 year to several years following the initial hemiconvulsion-hemiplegia episode. Focal seizures were considered to be mainly of temporal lobe origin.
In their more comprehensive study, Gastaut and associates considered previous publications of this condition, and on the basis of 150 cases, they described hemiconvulsion-hemiplegia-epilepsy syndrome as follows (24):
Some infants present, in the course of an acute febrile illness, one or many convulsions, sometimes an epileptic status, followed by an ipsilateral motor deficit. They show, upon recovery from the acute stage, a flaccid paralysis which is gradually replaced by a spastic condition and, months or years later, a chronic epilepsy, which is rarely of the sensory or motor type, but usually of the psychomotor type. This combination of initial hemiconvulsions and hemiplegia, free interval with possible regression of the motor deficit, and ultimate appearance of psychomotor epilepsy forms a clinical entity which has been known for some time but its clinical, electroencephalographical, radiological and pathological features have only recently been studied by the Marseille School, which proposed to call it: hemiconvulsion-hemiplegia-epilepsy.
Further studies (48; 49; 17; 16) have demonstrated that the initial episode may be observed in various situations and that the subsequent focal onset partial epilepsy can be temporal, extratemporal, or multifocal.
It can be argued that, taken separately, both the initial episode (hemiconvulsion-hemiplegia) and the subsequent development of epilepsy are not proper "syndromes." In fact, the hemiconvulsion-hemiplegia episode corresponds to a unique episode of focal status epilepticus responsible for a unilateral motor deficit, and the later development of epilepsy corresponds to a structural focal epilepsy. However, the stereotyped sequence of events that characterizes hemiconvulsion-hemiplegia epilepsy allows some authors to consider it as a syndrome (07). Thus, hemiconvulsion-hemiplegia-epilepsy was reintroduced as a syndrome by the ILAE Task Force on Classification and Terminology (22). In the published ILAE revised terminology and concepts report, hemiconvulsion-hemiplegia-epilepsy syndrome is considered a "clinically distinctive constellation" (14). In 2021, the ILAE Task Force on Nosology and Definitions proposal on epilepsy syndromes classification includes hemiconvulsion-hemiplegia-epilepsy syndrome as one of the “developmental and epileptic encephalopathy” syndromes with onset in childhood (55). The proposal is currently at the public comment stage before it is finalized.
According to an expert consensus definition, infantile hemiconvulsion-hemiplegia and epilepsy syndrome is a specific syndrome in a patient less than 2 years old, presenting as new-onset refractory status epilepticus with unilateral motor seizures, high-grade fever at the time of onset of refractory status epilepticus, and unilaterally abnormal acute imaging, followed by hemiparesis lasting at least 24 hours, and excluding definite infectious encephalitis (29).
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