Atypical absence seizures are similar to absence seizures but, as the name suggests, they are unusual or not typical. The child will stare, as with an absence seizure, but during an event, he/she will be somewhat responsive. Atypical absence seizures are similar to absence seizures but may have more pronounced motor symptoms such as tonic (stiffening) or clonic (jerking) spells or may have automatisms (involuntary behaviors) as seen in complex partial seizures. The EEG does not have the classic three-per-second spike and wave pattern seen in simple absence seizures. Like absence seizures, it can appear to observers as though the child is daydreaming or switching off so it may be hard to distinguish from the child’s usual behavior and therefore difficult to detect. They can occur many times a day and are often mistaken for daydreaming or look as though the child is zoning out or “not with it”.
In Doose syndrome, atypical absence seizures may be just one manifestation of this mixed seizure disorder. Atypical absence seizures often accompany clusters of myoclonic and/or myoclonic-atonic seizures. If these seizures occur frequently throughout the day, they can interrupt the child’s ability to function properly because his/her awareness (and the brain’s processing) is being constantly interrupted.
Like all of the generalized seizures, an atypical absence seizure starts suddenly and without warning but the shift in consciousness may be so subtle that it may be very difficult for an observer to detect when the seizure starts or finishes. Similar to an absence seizure, the child displays a glazed look and stares. However, unlike a simple absence seizure, the child may be somewhat responsive and also have more pronounced motor symptoms such as twitching of the mouth, eye blinking, mild head bobbing which may give the observer a clue that seizure activity is occurring. As is the case with all generalized seizures, the child is momentarily unconscious during the event so he/she doesn’t know what is happening, cannot recall anything, but in the case of an atypical absence seizure, he/she may be somewhat responsive to and aware of his/her surroundings.
These events may be so brief that they are observable only on the EEG which will show a spike and wave pattern that distinguishes it from a simple absence seizure. Sometimes the events may last 15-30 seconds or perhaps longer and, to the observer, there may be an obvious change in the child’s state of consciousness. Being somewhat responsive during a longer event, the child may have delayed reactions, seem out of character, be easily confused or agitated. The “somewhat responsive” feature of an atypical absence seizure may lead an observer to mistake the event for a complex partial seizure. Sometimes the seizures may go completely unnoticed because the event is indistinguishable from the child’s usual behavior. When the seizure ends, the child is usually alert afterward however he/she will have missed some of what is happening around him/her.