A clinical study of febrile myoclonus in children.

Fever is sometimes associated with chill, myoclonus, delirium and convulsion. We previously reported EEG findings of febrile delirium, when we found that 18% of patients showed febrile myoclonus simultaneously with febrile delirium. The purpose of this study is to clarify the clinical features of febrile myoclonus and to investigate the relation to febrile convulsion. Myoclonic episodes were studied in 11 patients, aged 8 months to 11 years. EEG was recorded in eight patients. In the past history, febrile convulsion was noted in two patients and one of them also had febrile delirium. The age range of patients with febrile myoclonus was similar to those developing febrile convulsion except for one case. The duration of febrile myoclonus was usually from several to 30 min, but was longer than 2 h in four patients. Seventy-three percent of patients showed fear, surprise and shouting. EEG was abnormal in four patients and spike components were found in two patients. Myoclonic jerks were seen during the EEG recording in two patients and EEG findings were not concordant with epileptic myoclonic attack. Ten patients were followed for 1-2 years, and none had afebrile seizures. Febrile myoclonus is a benign symptom associated with fever. Mood change, fear or surprise and shouting with myoclonic jerks may suggest action of cytokine on the hypothalamus induced by infection. Febrile myoclonus, delirium and convulsion were seen in one patient in his first 3 years of life. These three symptoms seem to appear in children depending on their predisposition.