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.

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.

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.

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.

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

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

The EEG is the most valuable test in the diagnosis of JME. An EEG performed in the morning in comparison with an afternoon session¹³ or an EEG record after sleep deprivation will yield a higher rate of abnormalities. However, continuous video-EEG monitoring provides definitive diagnosis. The characteristic interictal EEG pattern of JME consists of bilateral, symmetric, and synchronous discharges of 3.5–6-Hz polyspike-wave complexes (Fig. 23–1). The resting awake EEG background activity is uniformly normal with a well-developed alpha rhythm of 10–11 Hz.

The EEG correlate of the myoclonic jerks is a burst of medium to high amplitude 10–16-Hz polyspikes followed by irregular 1–3-Hz slow waves of different amplitude (Fig. 23–2). The bilateral symmetric polyspikes have maximum amplitude in frontal and central regions and are much less synchronized and regular than the classic 3-Hz spike-wave complexes seen in childhood absence epilepsy. A diffuse discharge of irregular 2–5-Hz spike-wave complexes may precede the multispike discharge.⁴ The usual EEG pattern of 1–10 seconds may last longer than the clinical seizure. Photosensitivity or the precipitation of bilaterally synchronous spike-wave patterns by intermittent photic stimulation is common in JME.¹⁴ Intermittent photic stimulation may also induce myoclonic jerks. Focal EEG abnormalities are described in as many as 30%–50% of the JME patients^15,16 (Fig. 23–3).

JME should be distinguished from the progressive myoclonus epilepsies, other primary generalized epilepsies, such as epilepsy with myoclonic absences, epilepsy with grand mal seizures on awakening, and partial epilepsies with focal motor seizures.

Not infrequently, JME, childhood absence epilepsy, and epilepsy with grand mal seizures on awakening occur in the same patient at different times in life. For example, childhood absence epilepsy may evolve to JME during adolescence.

JME carries an excellent prognosis as treatment with AEDs will control seizures in the majority of patients. The condition should be treated as soon as a diagnosis is made unless the only symptom is rare or stimuli-related myoclonic seizures. In this case, avoiding precipitants and careful followup may be appropriate.

Optimal management of the patient with JME should include not only selection of an appropriate AED but also control of precipitating factors and prevention of accidents and injuries in case of generalized tonic–clonic seizures. Patients with JME should be encouraged to establish regular sleep–wake cycles and avoid precipitating factors such as alcohol or illegal drugs and excessive fatigue. Patients with seizures precipitated by visual stimuli should avoid flickering lights or similar stimuli. Patients should be informed about the need for drug compliance and the risks of recurrence after drug withdrawal so that expectations will be realistic.