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Dravet's Syndrome
(severe myoclonic epilepsy in infancy)

By Charlotte Dravet
YOU CAN VEIW THE ENTIRE DOCUMENT INCLUDING CREDITS AT http://www.epilepsy.org/ctf/dravet.html
 



Severe myoclonic epilepsy in infancy was described by Dravet in 1978 (Dravet 1978). In 2002 Dravet and colleagues found at least 445 published cases.

CLINICAL MANIFESTATIONS

Severe myoclonic epilepsy begins during the first year of life. Development is normal prior to the onset of seizures. Affected infants develop either generalized or unilateral clonic seizures without prodromal signs. Myoclonic jerks and partial seizures usually appear later. Psychomotor retardation and other neurologic deficits occur in affected children.

The first seizure type that appears is a clonic seizure, either generalized or unilateral, often changing sides These seizures may be brief or long in duration. In many cases, the first seizure appears in association with fever. The febrile seizures in these cases often recur in 6 to 8 weeks and may be prolonged, leading to status epilepticus. Later in the course, the seizures may recur without rise of body temperature (Dravet et al 1992). These convulsive seizures, carefully analyzed with video-EEG recordings performed along the course, are polymorph. They can be clearly generalized, clonic and tonic clonic, or unilateral, hemiclonic.|{diagram:cdds1.bmp}{caption:Polygraphic recording of a convulsive seizure during sleep}{label:Association of asymmetric tonic-clonic components demonstrating a short hemiclonic seizure are seen in this 7-year-old girl. Onset occurs with a right discharge of polyspikes and polyspike waves. Then, the discharge involves the right hemisphere, spreading to the opposite side. Postictal right depression and slow waves are shown.}| More often, they have peculiar clinical and EEG features that do not permit classification under generalized clonic or tonic-clonic seizures. They are characterized by clonic or tonic components, initially predominating in the head and the face, evolving to variable, bilateral localization, and loss of consciousness. When they are short in duration there are no autonomic symptoms. They were named “falsely generalized” or “unstable” (Dravet et al 2002).

The second seizure type is myoclonic seizures. Typically they are generalized, involving the body axis and the proximal part of the limbs. They are accompanied by generalized spike-waves and polyspike waves in the EEG.|{diagram:cdds2.bmp}{caption:Polygraphic recording of massive myoclonias}{label:Numerous myoclonic jerks are associated with generalized spike-waves and polyspike-waves in the 5-year 10-month-old boy.}| Sometimes, they begin focally and are limited to one limb or the head prior to becoming generalized seizures (Dravet et al 2002). The myoclonic jerks are usually frequent, occurring several times a day. These myoclonic seizures are often associated with interictal segmental myoclonus.|{diagram:cdds3.bmp}{caption:Polygraphic recording of interictal myoclonias increased by movements}{label:The left side shows the patient at rest; the right side shows her in movement. Myoclonias are not associated with spike-waves.}|

The third seizure type is absence seizures, which are atypical and of rather short duration, with more or less rhythmical generalized spike-waves in the EEG.

The fourth seizure type is complex partial seizures with atonic or adversive and autonomic phenomena as well as automatisms. Occasionally they secondarily generalize.

The occurrence of status epilepticus is frequent, either convulsive (often febrile), or as obtundation status (Dravet et al 2002). The latter consist of an impairment of consciousness, variable in intensity, the presence of fragmentary and segmental erratic myoclonias, sometimes associated with a slight increase of the muscular tone. Convulsive seizures can either initiate or occur during or terminate these status. They are prolonged for several hours or days. The EEG shows a diffuse dysrhythmia of slow waves, intermixed with focal and diffuse spikes.

Psychomotor retardation is observed usually during the second year after the onset of seizures. Progressive neurologic deficits such as ataxia and corticospinal tract signs subsequently develop.

DIFFERENTIAL DIAGNOSIS

Since the first clonic seizures in severe myoclonic epilepsy are often associated with fever, distinction from febrile convulsions is important. In severe myoclonic epilepsy, (1) the onset is earlier (before 1 year of age) than in febrile convulsions, where the age of onset is between 18 and 22 months; (2) the seizure type is clonic and often unilateral instead of generalized tonic-clonic; and (3) the seizure episodes are more prolonged and frequent, even when treated. The diagnosis can be established if other seizure types, particularly myoclonic jerks and photically-induced spike-waves, are observed (Dravet et al 2002). When no myoclonias occur but the other seizure types appear (atypical absences, partial seizures, obtundation status), the diagnosis is also that of severe myoclonic epilepsy but in its variant without myoclonias.

Lennox-Gastaut syndrome is virtually excluded by a history of febrile clonic seizures in the first year of life and is characterized by drop attacks, atypical absences, axial tonic seizures, and specific electroencephalographic abnormalities.
Difficulties may arise in differentiating severe myoclonic epilepsy from myoclonic-astatic epilepsy. In some cases of the latter, there is an early onset with febrile convulsive seizures but during the course of the epilepsy there are neither partial seizures nor focalization on the EEGs, and the main seizure type is myoclonic-astatic (Doose et al 1998; Guerrini et al 2002).

The progressive myoclonic epilepsies due to storage could be evoked, but at this age run a different course and can be eliminated by biological and neurophysiological investigations and by fundus.

An early cryptogenic focal epilepsy may have the same onset with febrile convulsions rapidly associated with focal seizures; these patients will not present atypical absences and myoclonic jerks. This diagnosis is improbable when the hemiclonic seizures are alternating and when partial motor seizures affect different parts of the body (Sarisjulis et al 2000).

DIAGNOSTIC WORKUP

The diagnosis is based on the clinical findings described above. One must underline the great value of the hyperthermia as a triggering factor, even when the elevation of temperature is not very high, as well as hot bath and physical efforts (Awaya et al 1989; Dravet et al 2002).

PROGNOSIS AND COMPLICATIONS

The outcome of severe myoclonic epilepsy in infancy is unfavorable. The affected children will persistently be affected with seizures. Partial seizures disappear and myoclonic jerks disappear or attenuate. Convulsive seizures are mainly localized at the end of the night. Fever remains a triggering factor and can still provoke epileptic status. Neurologic abnormalities remain stable. All patients are cognitively impaired (severely in 50%). Many also have behavioral disorders, including psychosis. The mortality rate is very high, from 15.9% to 18% (Dravet et al 2002).

MANAGEMENT

Treatment is disappointing. Valproate and benzodiazepines (clonazepam, lorazepam) are the most useful drugs. Phenobarbital, potassium bromide (convulsive seizures), and ethosuximide (myoclonic seizures and absences) can help some children. The effect of vigabatrin is variable. Carbamazepine and lamotrigine often have an aggravating effect (Guerrini et al 1998; Wallace 1998). The helpfulness of ketogenic diet needs to be proven (Caraballo et al 1998). Recently, stiripentol (Chiron et al 2000) and topiramate (Coppola et al 2002; Villeneuve et al 2002) have been shown to be effective against the convulsive seizures and the status. It is important is to avoid the long, generalized, unilateral seizures by preventing infectious diseases and hyperthermia, which are their triggering factors.

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SYNONYMS

Dravet’s syndrome
Epilepsy with polymorphic seizures
SME
SMEI

GLOSSARY

Dravet syndrome (severe myoclonic epilepsy in infancy):Epileptic syndrome characterized by infantile onset, multiple seizure types, and progressive cognitive decline.

PERMUTED TOPIC, SYNONYMS, VARIANTS

Dravet syndrome (severe myoclonic epilepsy in infancy) severe myoclonic epilepsy in infancy,
Dravet syndrome myoclonic epilepsy in infancy, Dravet’s syndrome seizures,
Epilepsy with polymorphic polymorphic seizures, Epilepsy syndrome,
Dravet syndrome, Dravet’s

 

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