The name "severe myoclonic epilepsy of infancy" can be misleading, as myoclonic seizures are not often the presenting or most notable seizure type . The International League against Epilepsy denotes Dravet syndrome as the infant who usually presents with prolonged, unilateral, and/or generalized seizures in the setting of mildly elevated temperature, and then progresses to other seizure types and developmental impairment.
Other seizure types seen in Dravet syndrome include myoclonias, partial seizures, and atypical absences . These occur starting in the second or third year of life and can accompany the early seizures associated with fever Seizure flurries are not uncommon, and episodes of convulsive and nonconvulsive status epilepticus occur Myoclonic seizures variably affect axial musculature and cause violent drops or barely perceptible head nods . Subtle myoclonias are also noted as brisk jerks of the extremities and tend to abate with time Partial seizures, both simple and complex, also occur and can generalize . Atypical absences may occur and may be associated with a myoclonic jerk or nod
Intellectual stagnation coincides with the onset of these other seizure types Most authors describe a static encephalopathy, though regression does not exclude the diagnosis of Dravet syndrome Language and walking typically occur on time but do not develop normally More than half the patients with Dravet syndrome will develop variable degrees of ataxia, and about 20% develop subtle pyramidial signs .
The EEG lacks a specific signature or feature, and the MRI findings in Dravet are equally noncharacteristic . Nevertheless, a Hungarian series noted the occurrence of hippocampal sclerosis with serial studies through the course of the disease in a majority of patients who had normal MRIs at disease onset
Fortunately, Dravet syndrome is uncommon, with an estimated incidence of less than 1 in 20,000 to as few as 1 in 40,000, depending on the author. Many patients will have a family history of FSs or epilepsy. Nearly 75% of patients with a Dravet or Dravet-like phenotype will exhibit SCN1A gene mutations . These Dravet-like phenotypes have also been referred to as borderland SMEI syndromes (SMEIB) because, whereas these patients have seizures and encephalopathy, they lack one or two typical clinical or EEG findings such as generalized spike wave activity Dravet syndrome exists on a continuum with other severe epilepsies of infancy and is on the opposite side of this continuum from generalized epilepsy with febrile seizures plus (GEFS+), a milder phenotype of SCN1A gene mutations .
Any attempt to limit exposure to febrile illness is helpful (i e , avoid daycare-type settings) . Vaccinations are not contraindicated. Scheduled antipyretics and extra doses of antiepileptic medications around the time of vaccination may be useful A properly fitted helmet is advised for those patients who fall from their myoclonic seizures Providing families with abortive therapy, such as rectal diazepam, may allow for earlier treatment for episodes of status epilepticus
Opinions regarding efficacious medications vary, and no single agent stands out Treatment with valproic acid along with a benzodiazepine is commonly initially advocated Stiripentol, vigabatrin, and topiramate have demonstrated some efficacy in limited trials or reports . Some authors prefer clonazepam to clobazam . Newer trials with much older agents such as potassium bromide have shown promise against convulsive episodes Other drugs such as carbamazepine and lamotrigine can aggravate seizures The ketogenic diet may help some patients Immunomodulation with corticosteroids and immunoglobulins have limited efficacy and create further concerns about susceptibility to infection
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