Objective: To analyze the clinical aspects, radiological features and evolution of myoclonus and other movement disorders (MD) in children with progressive myoclonic epilepsies (PMEs).

Background: PMEs are a group of uncommon clinically and genetically heterogeneous disorders characterized by generalized epilepsy, neurological deterioration and myoclonus. Rarely, other MD may be associated with myoclonus.

Method: We conducted a retrospective study including a cohort of children hospitalized at the Department of Pediatric Neurology of the National Institute of Neurology of Tunis from 2005 to 2022, for PME. We analyzed the epidemiological, clinical, electrophysiological, radiological, genetic and therapeutic aspects of MD in PMEs.

Results: Thirty-three patients were included. The mean age at on-set was 5.6 years [4 months-16 years]. Sex ratio (M/F) was 0.6. Consanguinity was found in 82% of patients. Myoclonus was generalized (70%), distal (62%), and focal (30%). It was positive (90%), triggered by action (53%), sensory stimulation (47%) or surprise (20%). Sleep myoclonus were found in 18% of the patients. Other MD associated with myoclonus were found in 55 % of cases. These were: tremor (18%), dystonia (15%), stereotypies (12%) and chorea (9%). Clinal examination showed cerebellar signs (54%) and pyramidal signs (60%). Cognitive impairment was noticed in 87 % of cases, including intellectual disability (88%) and autism spectrum disorders (9%). Electroencephalography showed slow background activity (37%), generalized fast spike or polyspike (34%), and wave-discharges (33%). Photosensitivity was found in 12%. Cerebral imaging showed: Cerebral atrophy (42%), cerebellar atrophy (42%) and leukodystrophy (13%). Fundoscopy showed optic atrophy (15%), retinitis pigmentosa (9%) and retinal dystrophy (3%). The etiologies were as follows: Neuronal ceroid lipofuscinosis (33%), mitochondrial disease (15%), Gaucher’s disease (3%), Lafora disease (6%) and undetermined (27%). Myoclonus was drug-resistant in 40% of cases and 65% of the patients experienced a worsening of their disease despite treatment. Two patients died.

Conclusion: The aetiology remains undetermined in many PEMs despite advances in genetics. Careful analysis of MD’s characteristics may therefore be a key feature in the diagnostic approach to childhood PEMs.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/movement-disorders-in-children-with-progressive-myoclonic-epilepsies/