Post-Hypoxic Myoclonus


  • Post-hypoxic myoclonus (PHM) refers to myoclonus occurring after hypoxic brain injury resulting from a cardiac arrest, characterised by abrupt, irregular contractions of muscles that may be focal or generalised


  • Acute — starts within 48 hours after a cardiac arrest
  • Chronic — also known as Lance-Adams syndrome, refers to myoclonus that starts days to weeks after cardiopulmonary resuscitation in patients who regained consciousness (cognitive function may range from normal to absent)

Post-hypoxic myoclonic status epileptics (MSE)

  • acute PHM lasting more than 30 minutes (despite not representing true epilepsy)
  • Post-hypoxic MSE occurs in 30% to 40% of comatose adult survivors of CPR
  • difficult to control
  • associated with a very poor prognosis (considered an ‘agonal phenomenon’)


Post-hypoxic MSE

  • history of hypoxic brain injury (e.g. cardiac arrest)
  • comatose
  • start within 12–24 h, stopping after 24 h
  • Generalised, multifocal clonus
  • Hypoxic brain injury with neuronal necrosis

Lance–Adams syndrome

  • Aware, caution re sedation
  • Later onset, may become chronic
  • Usually intention myoclonus (i.e. exacerbated by the patient attempting to perform tasks)
  • Normally preserved intellect, + ⁄ – chronic myoclonus
  • Hypoxic brain injury without irreversible infarction

There are no specific EEG patterns that distinguish between the two conditions


Myoclonic status epilepticus

  • prognosis is extremely poor
  • In the largest published series of post-hypoxic MSE, Wijdicks and colleagues found that all 40 patients had intermittent generalized myoclonus involving both face and limb muscles. Stimuli, such as touch, tracheal suctioning, and loud handclaps triggered myoclonic jerks in most of the patients. None of the 40 patients who had acute post-hypoxic MSE awakened, improved in motor response, or survived.
  • meta-analysis of patients who had post-hypoxic MSE : of 134 pooled cases, 119 (88.8%) died, 11 (8.2%) remained in a persistent vegetative state, and 4 (3.0%) survived. Of the four patients who survived, two were described as having a good outcome.

Lance-Adams syndrome

  • chronic myoclonus may persist
  • cognitive function may range from absent to normal
  • high proportion remain unable to function independently in daily life

Single seizures and sporadic focal myoconus does not predict poor prognosis following anoxic brain injury



  • difficult and of questionable usefulness
  • medications used include: phenytoin, valproate, and benzodiazepines such as clonazepam.
  • IV anaesthesetic agents such as propofol and midazolam are often needed
  • Regardless of treatment the prognosis is poor due to the severity of underlying brain injury

Lance-Adams Syndrome

  • diagnosis requires that all sedatives have worn off
  • aggressive treatment may improve longterm function
  • pharmacological control of myoclonus with agents such as sodium valproate, clonazepam, and levetiracetam
  • rehabilitation to limit disabilities

References and Links


Journal articles

  • English WA, Giffin NJ, Nolan JP. Myoclonus after cardiac arrest: pitfalls in diagnosis and prognosis. Anaesthesia. 2009 Aug;64(8):908-11. PMID: 19604197. [Free Full Text]
  • Acharya JN. Post-hypoxic myoclonus: The good, the bad and the ugly. Clin Neurophysiol Pract. 2017 May 5;2:105-106 PMC6123932
  • Shin JH, Park JM, Kim AR, Shin HS, Lee ES, Oh MK, Yoon CH. Lance-adams syndrome. Ann Rehabil Med. 2012 Aug;36(4):561-4. PMC3438425.
  • Wijdicks EF, Hijdra A, Young GB, Bassetti CL, Wiebe S; Quality Standards Subcommittee of the American Academy of Neurology. Practice parameter: prediction of outcome in comatose survivors after cardiopulmonary resuscitation (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2006 Jul 25;67(2):203-10. PMID: 16864809. [Free Full Text]
  • Wijdicks EF, Parisi JE, Sharbrough FW. Prognostic value of myoclonus status in comatose survivors of cardiac arrest. Ann Neurol. 1994 Feb;35(2):239-43. PMID: 8109907.
  • Venkatesan A, Frucht S. Movement disorders after resuscitation from cardiac arrest. Neurol Clin. 2006 Feb;24(1):123-32. PMID: 16443134.

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Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

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