Myoclonic Seizures: Clinical Characteristics and Management

Clinical Characteristics

Myoclonic seizures are characterized by sudden, brief, involuntary jerks caused by muscular contractions or inhibitions, typically lasting only a fraction of a second, according to the European Society of Intensive Care Medicine 1
Myoclonic seizures can be symmetrical and synchronous or asymmetrical and asynchronous, with the latter being more common in syncope but can occur in epilepsy, as stated by the European Heart Association 2
The movements typically begin at or shortly after the onset of loss of consciousness in epileptic myoclonic seizures, as reported by the European Heart Association 2

It is essential to distinguish myoclonic seizures from tonic seizures, which are sustained muscle contractions, and syncope-related movements, which are typically fewer, asymmetrical, and occurring after loss of consciousness, according to the European Heart Association 2, 3
The term "myoclonus" is used for movements in syncope as well as for certain types of epilepsy, while "clonic" is typically restricted to epilepsy, as stated by the European Heart Association 2

Status myoclonus starting within 48 hours after cardiac arrest is associated with poor neurological outcomes, with a false positive rate of 0% [0-5%], though some patients can recover, as reported by the European Society of Intensive Care Medicine 1, 4
Patients with post-arrest status myoclonus should be evaluated off sedation whenever possible, and EEG recording can help identify awareness and reactivity, according to the European Society of Intensive Care Medicine 1, 4

Viral encephalitis, particularly measles virus, can cause myoclonic jerks, which may be associated with a characteristic EEG showing periodic complexes with a 1:1 relationship with the jerks 5
Nipah virus infection can lead to myoclonus along with dystonia, areflexia, and hypotonia 5
JC virus causing Progressive Multifocal Leukoencephalopathy (PML) in immunocompromised patients may present with myoclonic movements 5

Can be distinguished from syncope-related movements, which typically occur after loss of consciousness and fall, according to the European Society of Cardiology 6