RESUMO
Mycoplasma pneumoniae is a respiratory pathogen responsible for various upper and lower respiratory tract diseases. This also induces extra-pulmonary manifestations, with encephalitis being the most frequent and critical manifestation in pediatric populations. This report describes an 8-year-old boy who presented with repetitive motions in both hands, agitation, muttering and increased appetite after seizure. He had started treatment with antibiotics for M. pneumoniae infection 14 days prior to this event. Electroencephalography (EEG) showed slow and disorganized background rhythms and polymorphic slowing on both frontal areas, whereas brain magnetic resonance imaging was normal. He was diagnosed with M. pneumoniae-related encephalitis and treated with intravenous immunoglobulin (500 mg/kg/day for 4 days). After 3 days, his impulsive behaviors disappeared and, after 4 days, his EEG became normal. Abrupt hyperactive behavior in children may be a sign of M. pneumoniae-related encephalitis.