Fitting the general perception of what happens during a seizure episode, clonic seizures involve convulsions of the torso, arms and legs, as the muscles in these parts of the body undergo rapid cycles of contraction and relaxation. The repeated movements--called jerking--rarely manifest by themselves and often occur in conjunction with tonus, a state defined by significant increases in muscle tone and rigidity. The type of clonic seizure a person has depends on its duration and whether the seizure happens with or without tonus. According to epilepsy.com, various epilepsy syndromes and neurological conditions can present with one particular kind of clonic seizure or another.
Myoclonic Seizures
Myoclonic seizures involve brief one to two second jerks of the extremities (i.e., "lightning" or "shock-like" jerks), usually on both sides of the body. The movements created during the event can look awkward and sometimes be mistaken for clumsiness. Several epilepsy syndromes exhibit myoclonus, including juvenile myoclonic epilepsy (JME) and Unverricht-Lundborg disease. People with JME experience these seizures upon awakening or in response to flickering light. Patients with Unverricht-Lundborg disease experience them upon strenuous mental or physical activity, and as a result of sudden unexpected noises or psychological stress. Irrespective of condition, the anticonvulsant valproic acid (Depakote) manages myoclonus well.
Clonic Seizures
Clonic seizures also involve rhythmic spasm of the arms and legs, but unlike myoclonus will lateralize to one side of the body and last for a sustained period beyond the initial burst. While these seizures can occur in infants (e.g., manifesting differently than simple jitteriness), they usually disappear during development. Besides possible epileptic disorder, clonic seizures might indicate other neurological problems such as serotonin syndrome. Serotonin, a chemical messenger in the brain, plays roles in mood, appetite and sleep. Antidepressant drugs like selective serotonin reuptake inhibitors (SSRIs) or supplements like tryptophan raise serotonin levels. In a review published in the "New England Journal of Medicine," Drs. Edward Boyer and Michael Shannon state that serotonin overdose can lead to toxicity, signaled by mental confusion, sweating, elevated heart rate and hyperactive reflexes from clonic episodes.
Tonic-Clonic and Clonic-Tonic-Clonic Seizures
As its name indicates, tonic-clonic seizure designates an episode with both tonic (i.e., muscle locking) and clonic (i.e., involuntary convulsion) phases. Early in the tonic phase, the airways constrict forcing out breath and producing audible gasps. The individuals will then collapse and experience clonus, during which time they might bite their tongues or lose bladder control. Emerging from a tonic-clonic seizure, people will often feel confused and exhausted. It might take hours to recover. The Epilepsy Foundation states that tonic-clonic seizures represent the most common type of generalized seizure, although seizures following a clonic-tonic-clonic pattern can also occur.
References
- Epilepsy.com: All About Epilepsy & Seizures (A comprehensive guide on myoclonic, clonic and tonic-clonic seizures)
- National Institute of Neurological Disorders and Stroke: Myoclonus Fact Sheet
- The New England Journal of Medicine; The Serotonin Syndrome; E.W. Boyer and M. Shannon; July 2005.
- Epilepsy Foundation, Generalized Tonic Clonic Seizures Information Page
