F14. Febrile myoclonus on EEG; benign or epileptic?

Abstract

Introduction Febrile myoclonus is an infrequently seen entity in young children. It is thought to be different from febrile seizures and early childhood myoclonic epilepsy. These are reported to not carry an increased risk for epilepsy. Interictal EEG has been reported to vary from normal to generalized spike and wave discharges. Ictal EEG findings of febrile myoclonus are rare in the literature and usually described as not showing EEG correlate. Methods We describe a patient with febrile myoclonus with ictal and interictal EEG findings as well as follow up data of over 1 year. We compared findings with previously reported cases. Results 11 month old boy presented with febrile illness and brief jerks. He was a product of non-consanguineous marriage with unremarkable perinatal history and normal development. This was his first febrile illness and developed jerky movements within the first 24 h. Temperature was 39 °C. He appeared ill without nuchal rigidity or alteration of mental status. Brief myoclonic jerks mostly involving the upper extremities but sometimes the entire body were seen occurring every 2–5 min. Rest of the general examination was unremarkable. Labs revealed normal cell counts and electrolytes. An electroencephalogram(EEG) and MRI scan of the brain were obtained. EEG showed posterior background of 6–7 Hz with normal organization. Interictally there were intermittent generalized spike-wave complexes. The clinical myoclonic jerks were associated with generalized spike and wave discharges indicative of myoclonic seizures. Myoclonus resolved as the fever settled and his follow up EEG, 2 weeks later was completely normal for age. Chromosomal microarray and metabolic screening labs were normal. Patient had several febrile episodes after this when he did not develop febrile myoclonus. 1 year later parents reported 4 more similar episodes of self-resolved myoclonus while febrile. He developed one, 2 min typical generalized febrile seizure. At 2 years, he has not developed afebrile seizures and has normal development. Conclusion Febrile myoclonus is infrequent and likely under-reported. Fewer than 20 cases have been described in the literature. Febrile myoclonus is thought to be a self-limiting benign condition which does not lead to epilepsy. There are reports of concurrent febrile seizures. There is a lack of literature describing ictal EEG findings as most of the reported EEGs were done interictally. Differential diagnosis includes early childhood myoclonic epilepsy, genetic myoclonic epilepsies, and severe myoclonic epilepsy of infancy (Dravet Syndrome). Fever can potentially lower the seizure threshold and febrile myoclonus could be their initial presentation. Our patient had febrile myoclonus with an ictal EEG correlate unlike patients in the literature. Despite these findings the myoclonus was self-limiting and resolved with the resolution of fever and the EEG abnormalities were transient. He appears to have a benign course despite prominent ictal correlate.