The first symptom of Dravet syndrome is usually a long-lasting seizure (longer than 15 minutes) that occurs during an acute illness with fever or after vaccination, before the age of 12 months.
However, the diagnosis cannot be made on this single manifestation. This long-lasting seizure leads doctors to perform further investigations in order to understand the possible causes of this unusual event. Indeed, other neurological disorders can result in long-lasting seizures in infants, such as febrile seizures, or a malformation of a small part of the brain, or even brain injury taking place around birth.
Investigations include cerebral imaging (magnetic resonance imaging, MRI) and electroencephalographic (EEG) recording. Sometimes, in an emergency context, a lumbar puncture is performed to rule out a cerebral infection by examining the cerebro-spinal fluid. The results of these investigations are usually normal in children with Dravet syndrome.
Later on, seizures of other type and of shorter duration appear. It is with the appearance of these seizures and with the results of all the previous investigations that the diagnosis can be made.