Objective: We present a case report of adult onset Huntington’s disease (HD) with myoclonus as the main clinical feature.

Background: Myoclonus is seldom reported as a feature of adult onset (HD) and is not a component of the Unified HD Rating Scale (UHDRS). Proper diagnosis of HD is more challenging in the absence of more classic symptoms such as chorea.

Methods: Written consent for case report was obtained from patient’s mother.

Results: The patient is a 45 year old male currently living in long term care setting with a 15 year history of symptoms which included rest and action myoclonus, progressive cognitive decline, and dystonia.
Diagnosis was made by movement disorders specialist with confirmation via positive HD genetic test. Myoclonus occurred in bilateral upper extremities without stimulus sensitivity. The patient also exhibited dystonia in the form of bruxism, right torticollis, right laterocollis, and bilateral wrist flexion dystonia.

He was treated with valproate with marked relief at doses up to 500 mg twice daily.
Valproate treatment was complicated by thrombocytopenia which necessitated multiple interruptions in treatment.

Clonazepam up to 0.5 mg twice daily, either as monotherapy or in conjunction with valproate, provided moderate relief. Sedation was a limiting factor and led to dose adjustments.

Conclusions: Valproate and clonazepam were effective treatments for myoclonus in this HD patient. Their chronic use was complicated by potential side effects of thrombocytopenia and sedation, respectively.

References: This abstract may have been previously presented at the 2017 American Academy of Neurology meeting. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/myoclonus-in-adult-onset-huntingtons-disease/