What are they like?

Seizures of this kind start as a partial seizure—that is, they start in one limited area of the brain. The forms they take vary as much as other partial seizures. But then (sometimes so quickly that the partial seizure is hardly noticed) the seizure spreads throughout the brain, becoming "generalized." Here's how a couple of people with epilepsy described their secondarily generalized seizures:

• The seizures start with a tingling in my right thumb. In seconds, my thumb starts jerking. Soon, my whole right hand is jerking. I have learned that by rubbing and scratching my forearm I can sometimes stop the seizure. Other times the jerking spreads up my arm. When it reaches my shoulder, I pass out and people tell me that my whole body starts to jerk.
• I see this colored ball on my right side. It seems to grow until it fills up my whole view. Everything becomes like a dream and I don't feel real. It is the strangest feeling. Sometimes the seizure stops then, and sometimes it goes all the way and I fall to the floor and have a grand mal [tonic-clonic seizure].

How long do they last?

The generalized, convulsive phase of these seizures usually lasts no more than a few minutes, the same as primary generalized seizures. The preceding partial seizure is usually not very long. Sometimes this part is so brief that it is hard to detect.

Tell me more

These seizures are called "secondarily generalized" because they only become generalized (spread to both sides of the brain) after the initial or "primary" event, a partial seizure, has already begun. They happen when a burst of electrical activity in a limited area (the partial seizure) spreads throughout the brain. Sometimes the person does not recall the first part of the seizure. These seizures occur in more than 30% of people with partial epilepsy.

Who gets them?

They can affect people of all ages who have partial seizures.

What's the outlook?

Many seizures of this kind can be controlled with medication. If a person has tonic-clonic seizures that are not well controlled with medication, the doctor should investigate to see whether they might be secondarily generalized seizures that begin in a limited area of the brain. If they are, surgery could be an option.

What else could it be?

It may be difficult to distinguish these seizures from primary generalized tonic-clonic seizures, especially if they occur during sleep or are not witnessed by anyone else. Most convulsive seizures during sleep are secondarily generalized seizures that do begin as partial seizures.

How is the diagnosis made?

The EEG and MRI are often helpful in telling the difference between these seizures and primary generalized tonic-clonic seizures.

Topic Editor: Orrin Devinsky, M.D.
Last Reviewed:2/11/04