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OVERVIEW

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Juvenile myoclonic epilepsy (JME) is a common epilepsy syndrome classified as a type of idiopathic generalized epilepsy (IGE).1 The syndrome is also known as impulsiv petit mal or the syndrome of Janz.2 JME represents approximately 10% of all epilepsies. Seizures typically begin in early adolescence, most often between the ages of 12 and 18 years, with a mean age of onset of 14 years.

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The main characteristic symptom is sudden, mild to moderate myoclonic jerks that appear more frequently in shoulders and arms, although they can also affect neck or legs. They typically occur early after awakening. Consciousness is either not impaired or very briefly and mildly affected. Myoclonic jerks are the only seizure type in 5% of JME patients. More than 90% of patients have generalized tonic–clonic or clonic–tonic–clonic seizures,3 and a third also have absences.3,4 Myoclonic jerks precede the onset of generalized tonic–clonic seizures in almost half the patients. Common precipitating factors for seizures are sleep deprivation, alcohol intake, and fatigue.

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Although results of treatment in JME are often excellent, recurrence of seizures occurs in up to 90% of the patients after withdrawal of antiepileptic drugs (AEDs).4,5 Therefore, JME is considered a lifelong disorder and discontinuation of therapy is generally not recommended, even after long seizure-free periods.

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DIAGNOSTIC CRITERIA

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The diagnosis of JME is made from the clinical history and electroencephalographic (EEG) findings. A detailed clinical history can suggest the diagnosis of JME. The interview should focus on the presence of myoclonic jerks, specifically whether they result in dropping or throwing things in the morning, soon after awakening. A detailed and careful family history should also be obtained in order to reveal any history of myoclonic jerks or the presence of any IGE syndrome.

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The neurologic examination in JME is normal. This feature helps to distinguish JME from the progressive myoclonus epilepsies because of the lack of progressive neurologic deterioration, dementia, and ataxia.6 Patients with JME have been found to be somewhat immature, emotionally unstable, and disinhibited.7,8 Neuropsychological studies reveal that JME patients have serious impairments in frontal functions, meaning deficits in cognitive processes involved in planning, concept formation, elaborating strategies for the attainment of immediate or future goals, and verbal fluidity.9 Psychiatric disorders have been described in 47% of the JME patients at any time of life and the substantially increased number of personality disorders might be attributed to frontal lobe deficits.10

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Routine magnetic resonance imaging (MRI) studies are normal in JME and therefore rarely indicated. Quantitative MRI studies reveal cortical gray matter atrophy in the frontal and temporal lobes as well as subcortical gray matter volume increases in the superior mesiofrontal regions and progressive thalamic atrophy. These findings support the pathophysiological concept of JME as a disorder of thalamocortical circuits.11,12

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