Objective: To define the clinical, electrophysiological and etiological features of progressive myoclonus ataxia (PMA).

Background: PMA, formerly known as the Ramsay Hunt syndrome, is a progressive encephalopathy comprising myoclonus and cerebellar ataxia. Epileptic seizures and/or cognitive decline commonly extend this ‘pure’ syndrome to a more complex form. However, this ‘complex’ syndrome is hard to differentiate from other phenotypes presenting with myoclonus, such as progressive myoclonus epilepsy. Therefore, diagnosing PMA and recognizing the underlying etiology remain challenging as the syndrome is not well defined and no comprehensive overview is available.

Methods: Patients with myoclonus and ataxia were identified using an electronic database. Clinical notes of included patients were reviewed retrospectively for the clinical, electrophysiological and etiological characteristics.

Results: In total, 76 patients were included suffering from ‘pure’ myoclonus and ataxia (n=10), ‘complex’ myoclonus and ataxia combined with cognitive decline and/or epilepsy (n=31), myoclonus combined with cognitive decline and/or epilepsy without ataxia (n=13) and myoclonus without ataxia, cognitive decline and epilepsy (n=22). 45/76 patients showed a progressive course; patients suffering from ataxia significantly more often compared to patients without ataxia. Comparing clinical features in patients exclusively with a progressive course showed differences between patients suffering from PMA. The presence of action provoked myoclonus, ataxia of the trunk, an ataxic gait and dysphagia were more frequent in patients suffering from ‘complex’ PMA compared to the ‘pure’ form. Furthermore, comparing electrophysiological features in the same group of patients showed differences in burst duration; patients suffering from ‘complex’ PMA showed a burst duration of 50-100ms, significantly higher compared to patients suffering from myoclonus with cognitive decline and/or epilepsy without ataxia. In only 28/75 of all patients an etiological cause was identified (table 1).

Conclusions: ‘Complex’ PMA is characterized by a burst duration of 50-100ms and can be distinguished from ‘pure’ PMA by clinical features regarding the presentation of myoclonus and ataxia. The low number of differentiating clinical and electrophysiological features combined with the low rate of identified etiological causes show the necessity for a better definition and a comprehensive overview of PMA.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/reappraisal-of-progressive-myoclonus-ataxia/