Intention myoclonus in Huntington's disease

A patient is described with severe intention myoclonus which was made worse by treatment with L-Dopa and improved by clonazepam. Family history and examination of several siblings suggested the diagnosis of Huntington's disease. Subsequent to improvement of the myoclonus the patient appeared to have the rigid form of Huntington's disease. This case represents a unique expression for an otherwise well defined genetic abnormality. Stimulus activated myoclonus in a common feature of a number of disorders of the nervous system. Intention, or action myoclonus has been the subject of increasing interest because of its association with the syndrome of post-anoxic encephalopathy (1), although it may occur with other disorders as well. Many abnormal movements have been reported in Huntington's disease, but myoclonus is a relatively uncommon feature of this disorder and to our knowledge intention myoclonus has not been reported as a major symptom. We recently have evaluated a patient with disabling intention myoclonus and examined several members of his family who have typical Huntington's disease. We therefore report this case, a unique presentation of an otherwise well described movement disturbance.