What is post-anoxic myoclonus (Lance-Adams syndrome)?

From the Guidelines

Post anoxic myoclonus should be treated with clonazepam, valproic acid, or levetiracetam as first-line medications, with propofol or midazolam used for sedation in severe cases, as recommended by the most recent guidelines 1.

Treatment Approach

The treatment of post anoxic myoclonus involves addressing the underlying cause and providing supportive care.

• First-line medications include:
  • Clonazepam (0.5-2 mg three times daily)
  • Valproic acid (starting at 250 mg twice daily, titrating up to 1500-3000 mg/day)
  • Levetiracetam (starting at 500 mg twice daily, increasing to 1000-3000 mg/day)
• For severe cases, a combination therapy may be necessary.
• If myoclonus persists, adding piracetam (8-24 g/day) or zonisamide (100-400 mg/day) can be beneficial.

Sedation and Monitoring

• Sedation with propofol or midazolam may be required for status myoclonus in the acute setting.
• Patients should be monitored for medication side effects including sedation, cognitive impairment, and liver function abnormalities.

Prognosis

The prognosis varies based on the severity of the initial brain injury, with Lance-Adams syndrome (chronic post-hypoxic myoclonus) having a better outlook than acute post-anoxic myoclonus, as noted in recent studies 1.

Guideline Recommendations

The 2020 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations suggests treating seizures in post–cardiac arrest survivors, but notes that there is no direct evidence that seizure treatment improves critical outcomes in this patient population 1.

• The task force recommends using valproate and levetiracetam as first-line drugs in post–cardiac arrest seizure treatment.
• There is no direct evidence of undesirable effects of antiepileptic drug therapy in comatose post–cardiac arrest survivors, but treatment with sedatives and conventional antiepileptic drugs in high doses has the potential to cause delayed awakening, prolonged need for mechanical ventilation, and increased critical care days 1.

From the Research

Definition and Characteristics of Post-Anoxic Myoclonus

• Post-anoxic myoclonus, also known as Lance-Adams syndrome, is a rare movement disorder characterized by myoclonic jerks that are worse on action than at rest, and postural lapses, ataxia, and dysarthria 2, 3.
• The condition typically develops following hypoxic brain injury and can be resistant to pharmacological therapy 2.
• The disability caused by post-anoxic myoclonus can be profound, and treatment in the rehabilitation setting is exceptionally challenging 3.

Treatment Options for Post-Anoxic Myoclonus

• Levetiracetam has been suggested as a promising agent that can significantly improve functional level and overall quality of life of patients with post-anoxic myoclonus 2, 3, 4.
• Valproic acid and clonazepam are also commonly used in the treatment of post-anoxic myoclonus, often in combination with levetiracetam 3, 5, 4.
• The treatment strategy for post-anoxic myoclonus is best derived from the neurophysiology classification scheme categories, with cortical myoclonus being the most common type 5.

Clinical Classification and Prognosis of Post-Anoxic Myoclonus

• A clinical classification system for post-anoxic myoclonic status has been proposed, which identifies three distinct clinical semiologies: Type 1, Type 2, and Type 3 6.
• The classification system may be a useful bedside prognostication tool, with Type 1 patients having a better prognosis than Type 2 and Type 3 patients 6.
• The prognosis of post-anoxic myoclonus is generally poor, but rehabilitation interventions can significantly improve the quality of life of patients 4.