Brain stem encephalitis is a cardinal presentation of central nervous system involvement in enterovirus 71 infection, and manifests as myoclonus, ataxia, tremor, and autonomic dysfunction. A 2-month-old infant with enterovirus 71 brain stem encephalitis demonstrated continuous myocloni and tonic spasms. On admission, the patient's myoclonus, which mainly involved the shoulders and the arms, was considerably worse during wakefulness and occurred once or twice a minute. Several hours after admission, the myoclonic jerks steadily worsened, appeared ceaselessly every 1 to 2 seconds, and were intermixed with tonic spasms of all four extremities accompanied by crying. Video electroencephalography revealed a normal background without epileptiform discharges and no ictal electroencephalographic changes during the myoclonic jerks and tonic spasms. Complete remission was achieved without complications after completion of a 3-day immunoglobulin therapy. This case suggests that the brain stem may be a major origin site for not only myoclonus but also tonic spasm.
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