Focal seizures originate within cortical or subcortical structures of one hemisphere of the brain – either discretely localised or distributed more widely. They may be accompanied by awareness or impaired awareness. Generalized seizures start at a point within, and rapidly engage, bilaterally distributed networks.

They can include cortical and subcortical structures but not the whole cortex. They may be clonic, myoclonic, tonic-clonic, etc, or absence seizures.⁵ Unknown seizures can be focal or generalised.⁴ Seizures are also termed unknown if they have not been seen by anyone. These may happen to people living alone or at night, for example.⁶

Epilepsy may be diagnosed as combined generalised and focal where a clinician is unable to determine the epilepsy syndrome or cause. Examples include temporal lobe epilepsy, generalised tonic-clonic seizures in a 5-year-old with generalised spike wave, focal impaired awareness seizures and absence seizures in the same patient or not being able to determine whether tonic-clonic seizure is focal or generalised. Dravet Syndrome is an example of a focal and generalised epilepsy.⁶  

Accurate identification of seizures is fundamental to the correct treatment of epilepsy. For example, sodium channel blockers are effective in the treatment of focal seizures but can make generalised seizures worse.⁴