Myoclonic Jerks: Etiologies and Diagnostic Considerations

Epileptic Causes

Myoclonic seizures are characterized by sudden, brief, involuntary jerks lasting only a fraction of a second 1

Status myoclonus starting within 48 hours after cardiac arrest is associated with poor neurological outcomes, though some patients can recover 1, 2
Post-anoxic myoclonus may evolve into Lance-Adams syndrome with chronic action myoclonus in patients with good neurological recovery 2
EEG recording helps identify awareness and reactivity in post-arrest patients 1
Immediately review the medication list to identify drug-induced myoclonus, particularly from opioids, as this may be reversible 3
Opioid-induced myoclonus results from accumulation of toxic metabolites 3
Hypocalcemia may induce or worsen myoclonic movements 4
Hypomagnesemia can trigger myoclonic jerks 4
Glucose metabolism disorders are recognized causes 5

Viral encephalitis, particularly measles virus, causes myoclonic jerks with characteristic EEG showing periodic complexes with 1:1 relationship to jerks 6, 1
Nipah virus infection leads to myoclonus along with dystonia, areflexia, and hypotonia 1
JC virus causing Progressive Multifocal Leukoencephalopathy in immunocompromised patients presents with myoclonic movements 1
Creutzfeldt-Jakob disease (CJD) is characterized by rapidly progressive dementia followed by myoclonic jerks with bisynchronous periodic sharp wave discharges on EEG that have 1:1 relationship with jerks 6

Calcium-phosphate metabolism disorders including hypoparathyroidism, pseudoparathyroidism, and primary familial brain calcification 5
Hyperthyroidism 5
Kernicterus 5
Cerebrovascular disease 5
Brain trauma 5

Benign Myoclonus of Early Infancy (BMEI) is a nonepileptic disorder characterized by myoclonic jerks of the head and/or upper limbs occurring in clusters, mimicking infantile spasms but with preserved consciousness 5
Onset occurs in the first year of life, mainly between 4-7 months 5
Attacks usually cease by age 2 years 5
Ictal EEG, neurological status, and development must be normal to confirm diagnosis 5
Attacks are frequently triggered by excitement, frustration, postural changes, or sensory stimuli 5

Distinguish myoclonic seizures from syncope-related movements: epileptic myoclonus begins at or shortly after loss of consciousness, while syncope-related movements occur after loss of consciousness and fall, are typically fewer and asymmetrical 1
Distinguish myoclonic seizures from tonic seizures (sustained muscle contractions) 1
EEG monitoring is essential in patients with clinical seizure manifestations to detect epileptic activity 2

When evaluating myoclonic jerks, the following suggest secondary causes or alternative diagnoses: duration of attacks >1 minute, age of onset over 20 years, abnormalities in brain CT/MRI or presence of other neurologic/systemic problems, no response to anticonvulsants, and abnormal results of interictal examinations 5