Post Anoxic Status Epilepticus

The term myoclonic status epilepticus has been used to describe a variety of clinical states that have in common a prolonged period of frequent spontaneous myoclonic jerks. A reasonable general definition might be that myoclonus must occur either (1) at least once every 10 seconds for longer than 10 minutes or (2) at least once a minute for longer than 30 minutes. Myoclonic status may be associated with a wide range of etiologies and the presentation of and approach to myoclonic status epilepticus depends largely on the underlying etiology. Acute anoxic myoclonic status epilepticus (MSE )usually starts on the first or second day after the anoxic injury and lasts 1 to 5 days. It is typically considered a poor prognostic sign and it is always associated with coma. The facial muscles are preferentially affected by asynchronous or synchronous small amplitude jerks that may occur at regular or irregular intervals. They often increase in frequency and severity with stimulation of the patient. Prominent eye movements, including paroxysmal eye opening and upward eye rolling, are characteristic, though all muscle groups can be affected. Chronic anoxic myoclonic status epilepticus, as classically defined, Lance-Adams syndrome (LAS) presents days to weeks after the insult and persists for months to years. It was originally described in patients who have regained mental status but may present while the patient is still in coma or under sedation (Freund et al 2016). It is also most commonly seen in patients who have suffered a primary respiratory arrest with or without a subsequent cardiac arrest. As defined, Lance-Adams syndrome is often associated with good neurologic recovery. On a practical level the most important distinguishing feature is that acute postanoxic myoclonic status epilepticus is typically associated with other clinical and neurophysiologic signs of severe brain damage, such as absent brainstem reflexes or absent cortical response on somatosensory-evoked potentials. Neuroimaging, EEG monitoring, somatosensory-evoked potentials, and neuron - specific enolase levels should be considered in all cases of acute postanoxic myoclonic status epilepticus. Repeated clinical exams are also critical because favorable outcomes have been noted despite the presence of postanoxic myoclonic status epilepticus. Pupillary response and absence of bilateral N20 (cortical) responses on somatosensory-evoked potentials and EEG are regarded as some of the most reliable predictors. Therapeutic hypothermia and targeted temperature management has been shown to improve survival and neurological recovery after cardiac arrest and has become the standard of care for cardiac arrest . In a meta analysis of studies of cardiac arrest conducted when hypothermia was utilized, 211 patients with myoclonus (not necessarily myoclonic status), 9% (18) were considered to have good neurologic outcome (Sandroni et al 2013; Sandroni and Nolan 2015).Also in a retrospective review of The International Cardiac Arrest Registry, a multicenter cohort of cardiac arrest patients mostly treated with targeted temperature management, Seder and colleagues reported very similar findings (Seder et al 2015). The authors also found that 9% (44) of 471 patients with myoclonus after cardiac arrest were considered to have good functional outcomes .Seder and colleagues found that if myoclonus was not thought to be associated with epileptiform activity on EEG, the likelihood of a good outcome increased to 15% (Seder et al 2015). There is little agreement on the appropriate management of acute myoclonic status epilepticus following circulatory arrest.Treatment approaches range from adding 1 or 2 anti myoclonic agents in an attempt to suppress clinical jerking to use of IV anesthetics to suppress most or all epileptiform activity. Agents commonly used include benzodiazepines, sodium valproate, and levetiracetam, as well as lacosamide and brivaracetam. For the treatment of refractory cases of LAS, deep brain stimulation surgery has been performed with some initial encouraging results, but only in a few cases and it is still experimental at this time. In a case of perinatal hypoxia, the target of stimulation was the thalamus but in the other two cases the stimulation target was the globus pallidus internus.