Myoclonus is defined as a sudden brief involuntary muscle contraction arising from neuronal activity in the central nervous system. It can be non-epileptic in origin, arising from subcortical, brainstem or even spinal cord structures. Cortical myoclonus is a form of epilepsy, and this seizure type occurs in a variety of diverse clinical settings (Table 2.14). The effects of the seizures, the response to therapy and the outcome will vary in these different settings, but the principles of therapy are similar for all the myoclonic epilepsies. The myoclonus in idiopathic generalized epilepsy is generally well controlled on single drug therapy, whereas the myoclonus in the symptomatic generalized epilepsy, progressive myoclonic epilepsy or in the focal epilepsies are more difficult to treat, and drug combinations may be necessary.
The drug of first choice in all forms of generalized myoclonic epilepsy is valproate, which can be strikingly effective. Where valproate is not appropriate, alternative therapies include lamotrigine, phenobarbital, clobazam or
Table 2.14 Epilepsies with myoclonus as part of the phenotype.
• Idiopathic generalized epilepsies (IGE)
• Benign myoclonic epilepsy syndromes
• Severe myoclonic epilepsy syndromes of childhood
• Symptomatic epilepsies with generalized myoclonus (especially due to metabolic disease (inherited and acquired), infections, drugs, toxins, poisoning)
• Partial epilepsies with focal myoclonus (occipital lobe and fronto-central epilepsy)
• Progressive myoclonic epilepsies (PME)
clonazepam, levetiracetam, topiramate, felbamate, zonis-amide and piracetam.
Lamotrigine has a variable effect in myoclonus but can be tried especially in myoclonus in IGE and in focal epilepsy. Levetiracetam has not been subjected to controlled clinical trials and myoclonus is currently an unlicensed indication, but its excellent effect in myoclonus is clearly evident in routine clinical practice. Topiramate and felbamate are newer drugs for which there is anecdotal evidence of good anti-myoclonic action at least in some patients. Zonisamide is also used as second-line therapy for intractable myoclonus, and can occasionally have a striking effect.
More complex myoclonic epilepsy can be treated with piracetam. This extraordinary compound is the only drug uniquely effective in myoclonus and that has no effect in other types of epilepsy. The doses required for myoclonus are extremely high, but the drug is very well tolerated. It is primarily effective in cortical myoclonus, but may also have some value in other myoclonic syndromes.
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