Purpose-To determine the characteristics that permit diagnosis of the type of epilepsy beginning in the 1st year of life, and to determine from what age such characteristics are recognisable. Patients-From 430 non-selected patients who began having seizures in the 1st year of life and were referred to the neuropaediatric department of Saint Vincent de Paul Hospital, those with epileptic spasms as the first seizure type, those with recognisable aetiology, and those for whom early history was not reliable were excluded. Methods-For the remaining 140 patients, the age at which clinical and electroencephalogram (EEG) characteristics met those of recognisable epilepsy syndromes according to the ILAE classification was studied. Results-In most epilepsy syndromes, the diagnosis could be made within three months of onset of the disorder. The most diYcult was to distinguish cryptogenic localisation related epilepsy from severe myoclonic epilepsy in infancy. Repeat focal seizures and persisting spike focus were the earliest and most reliable signs of localisation related epilepsy, whereas alternating focal seizures, generalised myoclonus, and/or spike waves appeared before the end of the 1st year in most infants with severe myoclonic epilepsy. However, for 39 patients it was not possible to reach the diagnosis of a precise syndrome. Conclusion-For over three quarters of infants with cryptogenic/idiopathic epilepsy, it is possible to reach a syndromic diagnosis within the first months of the disease, based on clinical and EEG characteristics. However, for one quarter, no diagnosis is possible based on the currently available classification. (Arch Dis Child 2000;82:226-230)

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