We described a 58-year-old woman with herpes simplex encephalitis (HSE), who initially had fever and developed impaired consciousness. The most striking finding was high signal intensity in the temporal lobe(s) with the typical configuration known from CT. Five consecutive patients diagnosed with HSE (type 1) between June 2005 and June 2006 (three males, two females, mean age 44 [range 16-68] years) were included in this retrospective study. This study aimed to evaluate a possible beneficial effect of a therapy of acyclovir and corticosteroids versus acyclovir only. Anti-herpes simplex virus (HSV) 1 IgG and IgM antibodies elevated in both blood and cerebrospinal fluid. From these results, HSV1 infection was thought to be the preceding infection of ADEM. Although the clinical symptoms had improved significantly over three months, the high signal intense lesions on T1-weighted MR images were also detected in the left medial temporal lobe, the right insula, and the straight gyrus.
In addition, administration of acyclovir was also continued, considering the complication of HSV encephalitis. MRI T2-weighted scan performed at 2 months later after the onset of ADEM revealed disappearance of the lesions. Viral load did not differ significantly between acyclovir and acyclovir/corticosteroid-treated groups, suggesting that the use of corticosteroids in addition to acyclovir does not increase viral burden. It is difficult to distinguish between ADEM and HSV encephalitis because both of these diseases show various neurological symptoms. In our case, MRI was the most useful method for correct diagnosis of ADEM. The increased level of myelin basic protein, the elevated IgG index and the continuous positive oligoclonal IgG indicated continuous immunologic response against HSV in these lesions.