What is an UNKNOWN ONSET seizure? 

Seizure types are classified by describing the place a seizure begins. The brain is divided into two halves called hemispheres. If a seizure is described as having a focal onset, this means that the seizure begins in one specific area of the brain in one hemisphere. If a seizure is described as having a generalized onset, this means that when the seizure begins, both sides of the brain (both hemispheres) are involved.  

Doctors and nurses will classify a seizure as a focal onset seizure (partial seizure) or generalized onset (primary generalized) seizure if there is a high confidence level about the type of onset. Often it is hard to know if a seizure has a focal or generalized onset, and in these cases the seizure type is described as unknown onset. Unknown onset seizures may be described further by your doctor as being MOTOR (symptoms include involvement of muscles) or NON-MOTOR (symptoms do not involve muscles).  

Your care providers will order the tests they think may be helpful to try to determine if your seizures are focal or generalized onset. Tests which are requested frequently to help to determine the onset of seizures include EEG MRI and video EEG testing.