[Herpes simplex brainstem encephalitis presenting high intensity area on MRI--a case report].

A case of herpes simplex encephalitis with high signal intensity area in brainstem on MRI was presented. A 44 year-old woman suffered from oral aphthous ulcerations in the end of 1988, and then it improved naturally. Oral aphtha appeared again on February 1988 followed by resistant fever to antibiotics and right hemiparesis. She was admitted to our hospital on 25 February 1988. Neurological examination revealed mild consciousness disturbance, neck stiffness, right-side deviation of tongue with dysarthria and right hemiparesis with bilateral plantar extensor reflex. Right hemisensory deficit in all modalities and truncal ataxia was also detected. Some aphthous ulcerations were revealed in oral cavity, but there were no ulcers on genitalia nor uveitis. CSF showed 32 mononuclear cells/mm3, protein 52 mg/dl and glucose 97 mg/dl. CSF culture and india ink stain, and serum autoantibodies were all negative. EEG and CT scan with contrast enhancement showed no significant abnormalities. T2-weighted brain MRI revealed high intensity area in the center of the pons. Anti-herpes simplex virus (HSV) type I antibody titer (FA method) in both serum and CSF were highly positive. Neurological symptoms gradually improved on the therapy of aciclovir and adrenal cortico-steroid. High intensity area in the pons on MRI was also gradually reduced. In this case, complete diagnostic differentiation from neuro-Behçet disease was difficult, but this case did not meet its diagnostic criteria. From the change of anti-HSV antibody titer both in serum and CSF, we diagnosed this case HSV brainstem encephalitis presenting high intensity area in the pons on MRI which has never been reported.