Myoclonus (Movement Disorders August 2019)

Educational Objectives

The goal of this program is to improve diagnosis and management of movement disorders. After hearing and assimilating this program, the clinician will be better able to:

1. Classify myoclonus based on physiologic and etiologic axes.
2. Manage care of a patient who presents with myoclonus.

Summary

Definition: Myoclonus characterized by sudden, brief, lightninglike muscle jerks; amplitude of jerk may be large or small; movements occur within fraction of second; tics associated with urge or need to move to obtain relief; in contrast, myoclonic movements random and not controlled by patient.

Case: 75-year-old woman with diabetes mellitus, hypertension, and chronic obstructive pulmonary disease admitted with pneumonia; patient intubated and treated with antibiotics; after improvement and transfer to hospital room, patient developed myoclonic jerks; on examination, patient lethargic and confused; she exhibited generalized myoclonic jerks and asterixis; neurologic examination otherwise nonfocal.

Assessment of case: First steps comprehensive history and examination; myoclonus should be categorized as generalized or multifocal; clinician should note comorbidities such as metabolic disorders, conditions affecting liver and kidneys, evidence for infection of nervous system, and medications administered in hospital; many drugs cause myoclonus, including some antibiotics and sedatives; patient should undergo EEG to rule out seizures and imaging to exclude lesions in brain.

Follow-up of case: Comorbidities included diabetes mellitus with renal insufficiency; patient’s blood glucose level greater than 200 mg/dL; liver function tests slightly elevated but no jaundice observed; EEG showed diffuse slowing without epileptiform discharges; images of brain showed microvascular disease; generalized myoclonic jerks persisted although patient no longer on antibiotics.

Approach to case: Clinician should evaluate medication list and review with medical team whether changes in liver and kidneys reversible (if so, normalization of values may be sufficient to resolve myoclonus); inadequate clearance in patient with renal insufficiency may increase toxicity of some drugs and their metabolites.

Drugs associated with myoclonus: In addition to antibiotics, myoclonus may be associated with drugs that treat mood disorders (eg, lithium).

Classification: Myoclonus may be classified on physiologic and etiologic axes.

Cortical myoclonus: Cortex accounts for more than half of cases of myoclonus; converting some leads of EEG to surface EMG near area of myoclonus may shows correlation between EEG and myoclonus; in other cases, back averaging may be used to confirm cortical origin; findings consistent with cortical myoclonus include enlarged somatosensory evoked potentials, exaggerated long-latency reflexes, and brief discharges (less than 50 ms to 100 ms) on surface EMG discharge (longer discharges suggest subcortical origin); long-latency discharges studied by stimulating median nerve proximal to hand (similar to somatosensory evoked potentials); single pulses every few seconds normally expected to propagate to cortex; in relaxed patient, excitation insufficient to produce motor response; in patient with cortical myoclonus, motor cortex hyperexcitable and response observed at 50 ms to 60 ms and associated with spike in EMG.

Cortical-subcortical myoclonus: Found in patients with myoclonic seizures as feature of primary generalized epilepsy; in such patients, excitation occurs in entire circuit between cortex and subcortex as well as at cortical level; EEG shows generalized spike-and-wave discharges similar to those observed in juvenile myoclonic epilepsy or absence epilepsy; cortical-subcortical circuit generalizes electric discharges across cortex; in contrast, in patients with cortical myoclonus, only localized region of cortex hyperexcitable; for cortical-subcortical myoclonus (such as juvenile myoclonic epilepsy), drug of choice valproic acid; other treatment options include lamotrigine and levetiracetam; for primary cortical myoclonus, first-line therapy levetiracetam, which may be supplemented with clonazepam, and, if necessary, valproic acid.

Subcortical-nonsegmental myoclonus: Refers to myoclonus with wide range of possible origins (from subcortical thalami to subcortical brainstem nuclei); nonsegmental despite origination in brainstem; myoclonus-dystonia syndrome common example of subcortical nonsegmental myoclonus (origin uncertain but may be basal ganglia); other examples include opsoclonus-myoclonus syndrome and brainstem reticular myoclonus that may develop after hypoxia.

Segmental myoclonus: Refers to myoclonus affecting few segments of spinal cord or brainstem; segmental myoclonus associated with long discharges (200 ms to 300 ms) that occur rhythmically or semirhythmically; most common example palatal myoclonus; segmental myoclonus may originate in lesion in spinal cord and affect only few segmental muscles.

Peripheral myoclonus: Refers to myoclonus caused by abnormality in peripheral nervous system; hemifacial spasm most common example (irritation of cranial nerve VII, often by loop vessel near brainstem, leads to spontaneous discharges); other causes include lesions of brachial plexus (eg, secondary to radiation therapy) or lumbar plexus.

Etiologies of myoclonus: Physiologic myoclonus — normal phenomenon that includes startle reflex and hypnic jerks; if patient undergoes evaluation and neurologic examination normal, condition not cause for concern; essential myoclonus — pathologic entity; condition usually chronic but not associated with other disability or disorder of nervous system; epileptic myoclonus —refers to myoclonus in setting of seizure disorder; includes juvenile myoclonic epilepsy, absence epilepsy, and epilepsia partialis continua; symptomatic myoclonus — largest category of myoclonic disorders; refers to myoclonus secondary to another neurologic or medical condition such as storage disorder, hypoxic insult, genetic syndrome, neurodegenerative disease, or toxic-metabolic disorder.

Management of case: One week after reversal of metabolic abnormalities, patient continued to exhibit myoclonic twitching; EEG, surface EMG, somatosensory evoked potentials, or long-latency reflexes may be used to identify cortical myoclonus, which would indicate treatment with levetiracetam; if physiologic testing not possible or diagnosis cannot be established, clinician may treat empirically for cortical myoclonus (ie, most common type); if levetiracetam not effective, clonazepam next drug of choice.

Clinical pearls: Assessment of comorbidities key when diagnosing myoclonus; subacute onset of myoclonus often suggests inflammatory etiology; clinician should consider physiologic and etiologic axes.

Summary: Myoclonus is symptom, not diagnosis; to diagnose myoclonus, use organized approach based on classification of myoclonus; treatment best guided by physiologic axis.

Readings

Caviness JN. Myoclonus. Continuum (Minneap Minn) 2019;25(4, Movement Disorders).

Disclosures

For this program, the following was disclosed: Dr Caviness reports no disclosure.

Unlabeled Use of Products/Investigational Use Disclosure: Dr Caviness discusses the unlabeled/investigational use of anticholinergic medications, botulinum toxin, carbamazepine, clonazepam, deep brain stimulation, levetiracetam, sodium oxybate, and tetrabenazine for the treatment of myoclonus.

To view disclosures of planning committee members with relevant financial relationships, visit: legacy.audio-digest.org/continuumaudio/committee. All other members of the planning committee report nothing to disclose.

The material presented in Continuum Audio has been made available by the AAN for educational purposes only and is not intended to represent the only method or procedure for the medical situations discussed but rather to present an approach, view, statement, or opinion of the speaker(s), which may be helpful to others who face similar situations. Opinions expressed by the speakers are not necessarily those of the AAN, its affiliates, or the publisher. The AAN, its affiliates, and the publisher disclaim any liability to any party for the accuracy, completeness, efficacy, or availability of the material contained in this program (including drug dosages) or for any damages arising out of the use or nonuse of any of the material contained in this program.

Acknowledgements

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

CA080402

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.

More Details - Certification & Accreditation