Myoclonic Epilepsy Beginning in Infancy or Early Childhood Clinical Presentation

Updated: Jul 26, 2022
  • Author: Michael C Kruer, MD; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP, FANA  more...
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Once myoclonus is identified and confirmed to be associated with abnormal generalized discharges on EEG, it is important to ascertain the frequency and course of the patient’s myoclonus, as well as the time of onset. In order to better characterize the patient’s electroclinical syndrome, it is important to distinguish whether other seizure types co-occur, to carefully delineate neurodevelopmental progress (paying attention to evidence of regression), and to identify systemic manifestations of disease. Identification of a distinct epilepsy syndrome may guide diagnostic testing and management, and it may aid in prognostication and long-term care decisions.


Physical Examination

Brief, abrupt myoclonic jerks typically occur several times a day, but they may or may not be observed during an office-based examination. Manifestations often include head nodding, abrupt abduction of the arms, or sudden falls. Eyelid or facial muscles are affected commonly, although axial myoclonic jerks are most common and occur in 90% of patients. The differential diagnosis of rapid, brief, hyperkinetic movements includes tics and stereotypies. As with many paroxysmal episodic disorders of childhood, in questionable cases, having caregivers videotape spells of concern may be helpful, particularly if direct observation is not possible.

Myoclonic seizures commonly occur on awakening, and some may be precipitated by photic stimuli. In neurodegenerative disorders, myoclonic jerks may be precipitated by abrupt stimuli. Rarely, myoclonic seizures occur continuously as myoclonic status epilepticus with partial preservation of consciousness. This is a particularly prominent feature of Alper syndrome associated with POLG1 mutations. [8]

Although myoclonic seizures may occur as the sole type of seizure in some patients, they more commonly are associated with other forms of generalized seizures. Generalized tonic-clonic seizures are most common. Brief generalized clonic seizures or unilateral clonic seizures also may be seen. Atypical absence seizures occur in 40%, and pure atonic seizures may also occur.