There are two main types of seizures, and they are based on a clinical presentation and what we see on the EEG. The two big types are generalized seizures, where there's a big burst of electricity in the full brain all at once. Under this category, there are generalized tonic-clonic seizures, which is what everybody thinks of as a seizure, so jerking, stiff, and then jerking afterwards. There are also atonic seizures, which are drops, where the person just loses tone and drops to the floor. There are myoclonic seizures, which are little quick jerks, and there are the classic absence, or what was called petit mal seizures, where a person stares and zones out for a few seconds.
There's the seizures that come from one area of the brain, we call them focal seizures, or that other word, partial seizures. Partial and focal really mean the same thing, where they start in one area of the brain and spread. Then we use that word complex, so complex partial seizures, which means your consciousness is impaired, you're sort of not there, versus simple seizures, which means your consciousness is not impaired. So, a simple partial seizure, your arm could be just twitching a little bit. I could be having a conversation with you right now and I could be having a simple partial seizure. Or I could feel bugs or something weird in just one part of my body. That also can be a simple partial seizure. But if I look zoned out, spaced out, confused, then that's a complex seizure starting in one area of the brain. Just because they start in one area doesn't mean they can't spread to the rest of the brain and become what you were discussing, a generalized seizure, so it's important to differentiate where the EEG starts, what the symptoms look like, and how they spread.
The reason for differentiating between those also is because it helps with treatment. Certain medications can only be used for partial seizures and can worsen generalized seizures. So, generalized seizures, the whole brain lights up at once. Partial or focal seizures, the discharges start in one discrete area of the brain. They may or may not spread. Complex partial seizures are associated with a change in the level of consciousness, so they're usually not totally with it and talking during it. Simple partial seizures start in one place and there's no impairment of consciousness.