Scripties UMCG - Rijksuniversiteit Groningen
English | Nederlands

The clinical characteristics of progressive myoclonus ataxia

(2017) Veen, S. van der (Sterre)

Introduction – In 1921, the syndrome progressive myoclonus ataxia (PMA) was first described by Sir Ramsay Hunt. However, he did not formulate a definition and as consequence, the clinical phenotype is not clearly described and no underlying etiology can be identified in a majority of patients.
Objectives – The aim of this study is to describe the clinical characteristics of PMA. Furthermore, we will describe the clinical characteristics of isolated cortical myoclonus (ICM) as it could be the predecessor of PMA.
Methods – PMA is defined as myoclonus and ataxia with or without infrequent epilepsy (6 or less seizures/year). Adherent patients were identified from the University Medical Center Groningen, the Netherlands. In addition, patients were identified presenting with ICM. Data was retrospectively collected from the electronic patient files including general information, clinical course and progression of disease, underlying etiology, and the clinical phenotype focusing on myoclonus and ataxia.
Results – Twenty-two patients with PMA were identified. The syndrome is characterized by the median age of onset of 2 years (IQR 0.7-3.3). The presenting symptom was ataxia (n=15) at the median age of 2 years (IQR 1.8-5) followed by myoclonus at the median age of 4.5 years (IQR 2-7.5). In addition, infrequent epilepsy (n=6) began at the median age of 7 years (IQR 2.3-10.1). The course showed progression in 18 patients. An underlying etiology could be identified in 50% of the cases.
Eleven patients with ICM were identified characterized by a median age of onset of 14 years (IQR 7-22). The course showed progression in four patients. In this group, no underlying etiologies could be identified.
Conclusion – PMA is characterized by the onset of ataxia at a young age, followed by myoclonus and infrequent epilepsy. Considering ICM is characterized by an older age of onset, it is not suspected to be the predecessor of PMA. Furthermore, the prognosis of ICM is more favorable.

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