Myoclonic-astatic epilepsy of early childhood - clinical and EEG analysis of myoclonic-astatic seizures, and discussions on the nosology of the syndrome

Purpose: The aim of this study is to elucidate the clinical and neurophysio logical characteristics of the myoclonic, myoclonic-astatic, or astatic sei zures in patients with myoclonic-astatic epilepsy (MAE) of early childhood, and to discuss on the nosology of this unique epileptic syndrome. Subjects : The subjects included 30 patients, who fulfilled the following modified I nternational League Against Epilepsy (ILAE) criteria for MAE, and whose mai n seizures were captured by video-electroencephalographs (EEG) or polygraph s. The modified ILAE criteria includes: (1) normal development before onset of epilepsy and absence of organic cerebral abnormalities; (2) onset of my oclonic, myoclonic-astatic or astatic seizures between 7 months and 6 years of age; (3) presence of generalized spike- or poly spike-wave EEG discharg es at 2-3 Hz, without focal spike discharges; and (4) exclusion of severe a nd benign myoclonic epilepsy (SME, BME) in infants and cryptogenic Lennox-G astaut syndrome based on the ILAE definitions. Results: The seizures were investigated precisely by video-EEG (n = 5), pol ygraph (n = 2), and video-polygraph (n = 23), which identified myoclonic se izures in 16 cases (myoclonic group), atonic seizures, with or without prec eding minor myoclonus, in 11 cases (atonic group), and myoclonic-atonic sei zures in three cases. All patients had a history of drop attacks, apart fro m ten patients with rnyoclonic seizures. Myoclonic seizures, involving main ly the axial muscles were classified into those with mild intensity not suf ficient to cause the patients to fall (n = 10) and those that are stronger and sufficient to cause astatic falling due to flexion of the waist or exte nsion of the trunk (n = 6). Patients in the atonic group fell straight down ward, landed on their buttocks, and recovered immediately. Analysis of the ictal EEGs showed that all attacks corresponded to the generalized spike or poly spikes - and-wave complexes. In the atonic form, the spikeand-wave mo rphology was characterized by a positive-negative-deep-positive wave follow ed by a large negative slow wave. In two patients, the intensity of the ato nia appeared to correspond to the depth of the positive component of the sp ike-and-wave complexes. We did not detect any significant differences in th e clinical and EEG features and prognosis, between the atonic and myoclonic groups. Conclusions: Although the determination of exact seizure type is a prerequi site for diagnosing an epileptic syndrome, the strict differentiation of se izure type into either a rnyoclonic or atonic form, does not appear to have a significant impact on the outcome or in delineating this unique epilepti c syndrome. At present, we consider it better to follow the current Interna tional Classification of Epileptic Syndromes and Epilepsies until a more ap propriate system than the clinico-electrical approach for classifying patie nts with MAE is available. (C) 2001 Elsevier Science B.V. All rights reserv ed.