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At a glance

It is a relatively common inherited idiopathic generalized epileptic disorder affecting around 10% of individual presenting epilepsy during the childhood period. It is characterized by myoclonic jerks, generalized tonic-clonic seizures and, sometimes absence seizures shortly after awakening. This medical condition is typically observed between the ages of 12 and 18 as it manifests itself with brief episodes of involuntary muscle twitching occurring early in the morning. All individuals have normal intelligence.

Synonyms

Janz Syndrome; Juvenile Myoclonic Epilepsy of Janz; Impulsive Petit Mal.

Incidence

The incidence is estimated at 1:1,000 to 2,000 in the general population. It represents 5 to 10% of all epileptic patients, but the condition probably is underdiagnosed and most significant than believed. Seventeen percent to 49% of those with JME have family members with a history of epileptic seizures. A slight prevalence among females has been reported. Almost all cases of JME have an onset in around puberty or during adolescence. Juvenile myoclonic epilepsy is no longer considered a homogeneous disease but rather appears to be the result of an interaction of stronger or weaker expression of various endophenotypes seen in a spectrum disease.

Genetic inheritance

Exact mode of inheritance is not clear. One-third of JME patients have a positive family history of epilepsy. At least six loci were associated with this medical condition and four with known causative genes. Most of these genes are related to ion channels. There was one nonion channel gene reported to affect ion channel currents. Some authors reported association with human leukocyte antigen of chromosome 6; however, this has not confirmed by other studies.

Pathophysiology

Microscopic brain alterations (dystopic neurons in stratum moleculare, white matter, hippocampus, and cerebellar cortex) have been observed. Exact cause of this disorder remains unknown.

Diagnosis

Based on clinical grounds. Video electroencephalogram (EEG) monitoring of typical seizures is the standard criterion (but not necessary to establish the diagnosis). The diagnosis should be suspected in patients with myoclonic jerks favored by reproducible precipitating factors. Sleep-deprived EEG with activation procedures (hyperventilation, photic stimulation) is the most useful test in clinical practice.

Clinical aspects

The disorder usually begins in adolescence and is characterized by absence seizures in early age. As the child ages, it is followed by myoclonic jerks in the morning (1-9 years later) and then grand mal seizures (a few years later). Patients are normally intelligent and do not lose consciousness during myoclonic jerks. Precipitating factors include sleep deprivation, psychological stress, alcohol use, and menses. Physical examination is normal.

Precautions before anesthesia

Check anticonvulsant therapy (including doses of antiepileptics) and continue normal therapy until the morning of anesthesia and surgery. Premedication, preferably with a benzodiazepine, is mandatory to reduce ...

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