Metabolic disease, hypoxia, toxic processes, and infectious disease may cause focal or diffuse myoclonus. Myoclonus associated with epilepsy commonly is symmetric. Myoclonus is a component of several epilepsy syndromes and occurs before or as a part of both absence and generalized tonic-clonic seizures. One important syndrome to identify is juvenile myoclonic epilepsy because of the specificity of treatment with valproic acid. Atonic seizures cause a sudden loss of postural tone and may cause falling, with trauma to the head or body.
Convulsions are the most common type of generalized seizures.
These are characterized by loss of consciousness associated with apnea and violent contractions of the musculature of the trunk and extremities. Frequently, patients have mouth trauma and bladder incontinence. Salivation often increases, and both pulse rate and blood pressure rise during the seizure. Most generalized convulsions begin with a tonic phase, in which there is sustained contraction of all muscles with extended legs and either flexed or extended arms. Some patients may have only tonic seizures or only clonic seizures.