What are the signs and symptoms of the clonic phase of generalized tonic-clonic seizures?

Updated: Nov 27, 2017
  • Author: David Y Ko, MD; Chief Editor: Selim R Benbadis, MD  more...
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The tonic stage gives way to clonic convulsive movements, in which the tonic muscles relax intermittently for a variable period of time.

During the clonic stage, a generalized movement occurs at a rate of about 4-8 Hz. This is because phases of atonia alternate with repeated violent flexor spasms. Each spasm is accompanied by pupillary contraction and dilation. Some patients may bite their tongue or cheek.

The atonic periods gradually become longer until the last spasm. Voiding may occur at the end of the clonic phase as sphincter muscles relax. The atonic period lasts about 30 seconds. The patient continues to be apneic during this phase.

The convulsion, including tonic and clonic phases, lasts around 1-2 minutes.

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