Twenty-four-hour ambulatory EEG monitoring in infantile spasms.

Twenty-four-hour ambulatory EEG (AEEG) recordings were performed in 74 infants with West Syndrome (WS) who had not received corticosteroids before the recording. EEG analysis was performed visually for interictal background activity as well as for ictal events: spasms (isolated or in clusters) and other seizures either generalized or partial. Six hundred fifty-four seizures were recorded in 67 patients. Partial seizures (PS) were noted in 31 infants (51% of symptomatic WS cases, 33% of cryptogenic WS cases). In 14 patients, PS were immediately followed by a cluster of spasms consisting of a single ictal event. Patients with PS had an asymmetrical interictal background activity in 85% of cases, with no return to hypsarrhythmia between spasms in a given cluster. AEEG is a reliable method to detect and analyze ictal events in infants with WS. In this population, patients with unfavorable outcome of both epilepsy and psychomotor development have PS. Therefore, the existence of PS may contribute to etiologic diagnosis and prognostic evaluation.