TABLE 2.

Main features of symptomatic myoclonus associated with the underlying etiology. Different etiologies may share a common myoclonus type, as well as different types of myoclonus may be present in the same condition.

Symptomatic myoclonus	EEG pattern	Myoclonus features
		Distribution Occurrence Origin
Post‐hypoxic cerebral damage
Acute: MSE	Burst suppression with PSW (4 stages)	Generalized/multifocal Spontaneous/reflex Cortical
Chronic: LAS	Normal/nonspecific /PSW or focal spikes	Multifocal Reflex/action Cortical /subcortical (reticular)
Infectious diseases
SSPE	Periodic—pseudo periodic complexes	Usually generalized Spontaneous Cortical/ subcortical
HSV Encephalitis	Lateralized periodic discharges	Focal Spontaneous Cortical
Metabolic disorders
Acute and chronic kidney disease	Nonspecific	Generalized/multifocal Reflex/action Subcortical (reticular)/cortical
Hepatic encephalopathy	Diffuse triphasic waves	Generalized/multifocal Spontaneous/action Cortical–subcortical
Reactions to drugs or toxic substances	Nonspecific	Generalized/multifocal Reflex/action Not determined
Progressive myoclonus epilepsies (PMEs)
		Generalized/multifocal Spontaneous/action/reflex Cortical
Dementia/neurodegenerative
CJD	Diffuse periodic triphasic waves	Generalized/multifocal Spontaneous/action/reflex Cortical–subcortical
AD	SW/ (central focal transient)	Generalized/multifocal Spontaneous/action/reflex Cortical
Huntington disease	SW/ (central focal transient)	Generalized/multifocal Spontaneous/action/reflex Cortical
Corticobasal degeneration	Not specific	Generalized/multifocal Spontaneous/action/reflex Subcortical/cortical

Abbreviations: AD, Alzheimer's disease; CJD, Creutzfeldt–Jakob disease; HSV, Herpes simplex encephalitis; LAS, Lance–Adams syndrome; MSE, myoclonic status epilepticus; SSPE, subacute sclerosing panencephalitis; SW, sharp and wave complexes.