Clinical characteristics and etiology of transient myoclonic state in the elderly

• Transient myoclonic state in the elderly is a peculiar type of myoclonus.
• We investigated the clinical features of this myoclonic disorder in 26 patients.
• Single myoclonic bursts were 44.4 ± 12.3 ms long with 9.5 ± 2.5 Hz contractions.
• The pathophysiology may include age-related metabolic or arteriosclerotic changes.
• Its prognosis is benign, and oral administration of clonazepam is effective.

ObjectivesTo clarify clinical picture of transient myoclonic state in elderly patients.MethodsThe Aizawa Hospital database was searched to identify all patients with transient myoclonic state with or without asterixis between April 2006 and June 2013. Medical records, brain images and laboratory data including electroencephalograms and electromyograms were reviewed.ResultsWe found 26 patients: 10 women and 16 men, and their ages ranged from 56 to 96 years (79.7 ± 9.9 years, mean ± standard deviation). The affected sites of the myoclonic jerks were predominantly the lower face, neck and upper extremities. The myoclonus appeared at conscious resting condition, slightly exaggerated by posturing or action. Asterixis was observed in eight patients. Single myoclonic bursts were 1.70 ± 0.94 s long. The interval of myoclonic bursts was 4.47 ± 2.44 s. Single myoclonic bursts were composed of 9.5 ± 2.5 Hz myoclonic contractions, and single myoclonic contractions were 44.4 ± 12.3 ms in duration. Most of the patients suffered from chronic diseases, but they were basically independent in activity of daily living. Oral administration of clonazepam was effective.ConclusionsTransient myoclonic state has relatively stereotyped features. The pathophysiology may include some metabolic abnormality on a background of age-related arteriosclerotic changes. Its prognosis is benign, and prompt oral administration of clonazepam abolishes it. Further investigations will be needed to clarify its cause and pathophysiology.