Evaluation of new-onset myoclonus in the hospitalized patient

EEG: electroencephalography; CSF: cerebrospinal fluid; EMG: electromyography; MRI: magnetic resonance imaging; SEPs: somatosensory evoked potentials.
* Drugs that may precipitate or exacerbate myoclonus:

• Psychiatric medications (eg, tricyclic antidepressants, selective serotonin reuptake inhibitors, monoamine oxidase inhibitors, lithium).
• Antibiotics (eg, penicillins, cephalosporins, quinolones).
• Narcotics (particularly meperidine and morphine).
• Antiseizure medications.
• Anesthetics.
• Contrast media.
• Cardiac medications (eg, calcium channel blockers, antiarrhythmic agents).
• Drug withdrawal from certain agents (eg, sedatives).

¶ Laboratory tests for myoclonus generally include:

• Electrolytes (including calcium and magnesium).
• Bismuth.
• Glucose.
• Renal and hepatic function tests.
• Thyroid antibodies and thyroid function tests.
• Vitamin E level.
• Paraneoplastic antibodies.
• Drug and toxin screen if clinical suspicion of undisclosed substance intake or use of illicit or prescribed psychoactive medications.
• Infection workup if encephalopathy or localizing signs of infection, fever, or leukocytosis.
• Lumbar puncture and CSF analysis in cases with encephalopathy, signs of infection, suspicion for immune-mediated disorder, or suspicion for prion disease.

Δ Clinical electrophysiologic testing, used to distinguish involuntary movements and to determine anatomic and physiologic classification of myoclonus, may employ multiple techniques, including:

• Surface EMG.
• Simultaneous electroencephalography-electromyography polygraphy (EEG-EMG polygraphy).
• SEPs.
• Jerk-locked back-averaging of EEG transients and/or SEPs to EMG discharges.
• Long latency EMG responses to peripheral nerve stimulation (eg, C reflex).

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