[A case of brainstem encephalitis caused by herpes simplex virus type 1 with possible infection via trigeminal nerve].

A 24-year-old man was admitted to our hospital because of consciousness disturbance, a stiff neck and various brainstem symptoms including a right one-and-a-half syndrome and right peripheral facial palsy a week after an episode of pharyngitis and right facial herpes simplex. Magnetic resonance imaging of the brain on admission showed high-signal intensities in the right pontine tegmentum, right cerebellar peduncle and vermis on fluid-attenuated inversion recovery imaging. Examination of cerebrospinal fluid yielded mononuclear pleocytosis, elevated protein and increased IgM antibodies to herpes simplex virus (HSV) by enzyme immunoassay. HSV-1 specific antibodies also were detected in serum by neutralization test. We gave a diagnosis of brainstem encephalitis caused by HSV-1. The patient was successfully treated with high dose of acyclovir, steroid and intravenous immunoglobulin. He was discharged without any neurologic sequelae. We herein presented a case of atypical encephalitis due to HSV-1 involving mainly the brainstem with possible infection via right trigeminal nerve and summarized recent 35 cases with herpetic brainstem encephalitis since 1990.