Amantadine Associated Myoclonus: Case Report and Review of the Literature

Abstract

Purpose: Amantadine is commonly used to treat Parkinson’s disease. A case of myoclonus and asterixis was associated with amantadine is reported. Case Summary: An 80-year-old man with Parkinson’s disease diagnosed in 2015 was started on amantadine for treatment of progressive tremor and orofacial dyskinesias induced by levodopa. He took amantadine 100mg orally daily for 7 days, then increased to 100mg twice a day thereafter. The patient complained of “worsening tremor” after 9 days and amantadine was decreased to 100mg daily. After 1 month on this dose, the patient reported that his “tremor” persisted and experienced visual hallucinations. His examination demonstrated diffuse myoclonus throughout his extremities and trunk, as well as asterixis when attempting to stand or holding his arms antigravity. Laboratory testing for renal and hepatic failure was unrevealing. Amantadine was reduced to 50mg daily for 4 days and then discontinued. Myoclonus resolved 3 days after discontinuation of amantadine. Conclusion: While amantadine-induced myoclonus is rare, health care providers should be vigilant in monitoring for signs and symptoms of myoclonus following amantadine initiation.