Clonic seizures are similar to generalized tonic-clonic seizures but consist only of rhythmic or semi-rhythmic contractions of a group of muscles. (That is, there is no tonic phase.) These jerks can involve any muscle group. The arms, neck, and facial muscles are most commonly involved.

Clonic seizures are much more common in children than adults.

Adapted from: Holmes GL. Classification of seizures and the epilepsies. In: Schachter SC, Schomer DL, eds. The comprehensive evaluation and treatment of epilepsy. San Diego, CA: Academic Press; 1997. p. 1-36.
With permission from Elsevier (www.elsevier.com)
Reviewed and revised January 2004 by Gregory L. Holmes, MD, Dartmouth Medical School