A 19-year-old man was transferred to our emergency department after the onset of convulsions and loss of consciousness in March 2016. The patient had a medical history of febrile seizures in childhood. He had not received influenza vaccination during the season. Initially, the patient's body temperature had risen to 38.5C at home, and he had presented with convulsions and loss of consciousness 7 hours following the onset of a fever. The patient did not have a cough, nasal discharge, sore throat, headache, arthralgia, or sore muscles. In the emergency room, he appeared to be a well-developed, well-nourished man. His body temperature was 39.1C, blood pressure was 139/68 mmHg, pulse was 96 beats/min, respiratory rate was 21 breaths/min, and oxygen saturation was 97% on room air. The Glasgow Coma Scale (GCS) score was 4 for eye opening (E), 4 for best verbal response (V), and 6 for best motor response (M). The physical examination was unremarkable, and his pupillary reflexes were normal. Neck rigidity and Kernig's sign were not apparent. He had a generalized convulsion lasting 1 minute in the emergency room.
The nasopharyngeal swab sample was analyzed using a rapid test kit (Quick Chaser Flu A, B; Mizuho Medy, Japan) and did not indicate the presence of either influenza A or B viral antigen. An initial laboratory examination showed a white blood cell count of 4,500 /muL (62% neutrophils), C-reactive protein level of 1.46 mg/dL, blood urea nitrogen level of 8.8 mg/dL, and creatinine level of 1.06 mg/dL. The serum interleukin (IL)-6 level was 9.06 pg/mL (normal range, <2.41 pg/mL). Lumbar puncture was performed, and a cerebrospinal fluid analysis revealed a normal cell count (<1 /muL), a protein level of 27.9 mg/dL, and a glucose level of 94 mg/dL. A computed tomography (CT) scan of the brain and chest radiograph showed normal findings. The anti-influenza virus treatment peramivir was started based on the information that there had been an outbreak of influenza A and B virus infections in the area during that time.
After admission, the patient's consciousness level worsened. He was somnolent with closed eyes. The GCS score was 12 (E2V4M6). Brain T2- and diffusion-weighted MRI on the same day showed multifocal high-signal lesions in the right parietal and frontal lobes, indicating acute encephalopathy (Fig. 1). On day 2 following admission, a repeated examination of a nasopharyngeal swab sample indicated the presence of influenza B virus antigen. The patient was treated with peramivir (300 mg/day) and methylprednisolone (1,000 mg/day) for 3 days. An EEG on day 5 showed diffuse slowing of the background activity consistent with encephalopathy (Fig. 2). The patient's physical condition gradually improved (Fig. 3). The serum IL-6 level was decreased to 0.673 pg/mL on day 8. The patient was discharged without any neurological impairment on day 10 and has been followed up at an outpatient clinic. An examination showed no evidence of underlying diseases or immunodeficiency. His serum levels of immunoglobulin G, A, and M were normal. Brain MRI and EEG on day 20 following the onset showed no abnormal findings. In addition, the serum antibody titers against influenza B virus, as measured using the complement fixation test, were 1:8 on admission and 1:64 on day 20. The serum antibody titer against influenza A virus was not found to be increased at admission or throughout the clinical course.