Epilepsy with myoclonic absences: Electroclinical characteristics in a distinctive pediatric epilepsy phenotype

• Largest series from the Indian subcontinent on a rare electroclinical phenotype
• Focal semiology and atypical fast/slow ictal onset patterns noted in a minority
• Sleep activation of generalized spikes noted may contribute to cognitive deficits.
• Age of onset earlier than other idiopathic absences of childhood
• Response noted to valproate or in combination with lamotrigine in one-third

PurposeThe purpose of this article was to study the electroclinical characteristics and seizure outcome of children with epilepsy with myoclonic absences (EMA).MethodIn this descriptive cohort study, we reviewed clinical records of patients who met the criteria for EMA. Each patient's demographic data, birth/developmental history, seizure semiology/pattern, antiepileptic drugs (AED), clinical examination, video-electroencephalography (VEEG), and neuroimaging data were reviewed. Response to AED and change in seizure frequency/pattern on follow-up were noted. Responders were defined by seizure freedom/>50% reduction in seizure frequency on follow-up.ResultTwelve children were diagnosed with EMA between 2008 and 2013 [50% male; mean age of onset: 3.5 years]. Main seizure types were the characteristic myoclonic absences (100%) and generalized tonic–clonic seizures (42%). Ictal correlate on VEEG was 3- to 3.5-Hz spike-and-wave discharges (82%) and fast recruiting bifrontal rhythm (25%). One patient had specific MRI abnormalities. Mean duration of follow-up was 23.9 months. Seizure frequency had significantly improved on follow-up (p = 0.005), and at last follow-up, nine patients were in the responder group: four seizure-free for at least 1 year, two with > 90%, and three with > 50% reduction in seizure frequency. The number of AED reduced significantly between initial visit and last follow-up among responders. Two patients on follow-up developed different seizure patterns, with generalized tonic and complex partial seizures. One responder expired because of unprovoked generalized convulsive status epilepticus.ConclusionThis cohort, the largest from the Indian subcontinent on the rare syndrome of EMA, suggests mild heterogeneity in a seemingly homogenous electroclinical phenotype. Clinical semiology while unique may demonstrate focality and variable ictal patterns. Most patients respond to either valproate monotherapy or valproate–lamotrigine combination; however, the prognosis remains guarded. The seizures of a minority of patients remain drug-refractory and may evolve into tonic or complex partial seizures.