[A mild form of brain stem encephalitis due to herpes simplex virus].

A 10-year-old boy had gait and speech disturbances 17 days after the initial symptoms of a fever, headache and cough. Four days later he was admitted to a hospital with mild disturbances of gait, speech, writing, visual acuity, left facial nerve, nystagmus and consciousness. Impairments of cranial nerves (II, III and VII), pyramidal sign and cerebellar sign were noticed. EEG showed generalized slow waves. Auditory brain stem response showed prolongation of the interval between I and V waves and poor differentiation between them. Brain CT could not find any abnormalities. Brain stem encephalitis was diagnosed. Clinical signs and symptoms continued for two weeks when steroid therapy was started and it was effective to improve the disease. He was discharged from the hospital without sequelae. Herpes simplex virus (HSV) type 1 was detected from cells in CSF on admission by fluorescence antibody method. HSV antibody titers in sera changed from 1/8 to 1/64 during three months by complement fixation test. Specific IgG and IgA by enzyme linked immunosorbent assay (ELISA) was high in CSF. Specific antibody in CSF/total antibody in CSF: specific antibody in serum/total antibody in serum for IgG and IgA classes were more than 1. Reports of mild type of HSV brain stem encephalitis seemed to be rare. Our case which was followed for several months carefully would be important to discuss.