Post-Hypoxic Myoclonus (PHM)

OVERVIEW

• 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

Types

• 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’)

DISTINGUISHING  FEATURES

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

PROGNOSIS

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

MANAGEMENT

MSE

• 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

Lifeinthefastlane.com

• CCC — Hypoxic brain injury

Journal articles

• English WA, Giffin NJ, Nolan JP. Myoclonus after cardiac arrest: pitfalls in diagnosis and prognosis. Anaesthesia. 2009 Aug;64(8):908-11. doi: 10.1111/j.1365-2044.2009.05939.x. PubMed PMID: 19604197. [Free Full Text]
• 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. doi: 10.5535/arm.2012.36.4.561. Epub 2012 Aug 27. PubMed PMID: 22977784; PubMed Central PMCID: 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. Review. PubMed 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. PubMed PMID: 8109907.
• Venkatesan A, Frucht S. Movement disorders after resuscitation from cardiac arrest. Neurol Clin. 2006 Feb;24(1):123-32. Review. PubMed PMID: 16443134.