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In spite of high rates of morbidity and mortality in herpes simplex virus (HSV) encephalitis, however, it is one of the exceptional viral infections with specific and effective therapy. In this report a HSV encephalitis case who was clinically unresponsive to acyclovir treatment, has been presented. An 11 months old girl patient has been brought to our clinic with the complaints of high fever and focal convulsions. Analysis of cerebrospinal fluid (CSF) revealed decreased glucose level and abundant red blood cells, despite it was not traumatic. The other CSF biochemical findings were found normal. Viral serology performed with CSF yielded negative result for HSV-1 IgG, positive result for HSV-2 IgG, and negative result for HSV-1/2 IgM, however, antibody index could not be estimated since it was not possible to obtain a simultaneous serum sample. Cranial magnetic resonance imaging (MRI) showed contrast material enhancement on bilateral temporal lobes. There was no growth in the CSF cultures. Acyclovir therapy (30mg/kg/day) was started with the prediagnosis of herpes encephalitis. In the third week of therapy CSF analysis was repeated because of the presence of partial paroxysmal attacts and absence of sufficient clinical improvement. In this CSF sample HSV-1 DNA was found positive by real-time polymerase chain reaction. Since CSF findings were still abnormal and the clinical picture worsened despite 21 days of therapy, the dose of acyclovir was increased to 60 mg/kg/day (3 weeks) with a possible drug resistance problem. Control brain MRI showed contrast enhancement on bilateral temporal lobes, with more intensivity in left, and encephalomalacia. Valproic acid and haloperidol were given to the patient for the treatment of permanent partial paroxysms and orofacial dyskinesis, developing in the follow-up period, respectively. After getting these complications under control, the patient was discharged and taken into follow-up. As a result, although it could not be possible to confirm the drug resistance by molecular methods, it was thought that this might be both a clinical and virological resistance phenomenon, because of the detection of HSV-DNA in the CSF sample during the period of severity of the illness.

In this report, characteristics of two cases of Herpes simplex virus (HSV) encephalitis with normal cerebrospinal fluid (CSF) findings at the time of admission have been discussed and the current literature has been reviewed. The diagnosis of the cases (one was 23 years old male, and the other was 75 years old female patient) was made on the magnetic resonance imaging (MRI) findings concordant with HSV encephalitis, together with HSV-1 DNA positivity by polymerase chain reaction (PCR). Both of the patients were treated with acyclovir (3 x 750 mg/day) lasting for 15 days and 21 days, respectively. The first male patient recovered with mild neurological defects, whereas the second female patient died because of nosocomial pneumonia and septicemia. In conclusion, even the CSF findings are normal, in cases considered to be HSV encephalitis, MRI should be the first radiological diagnostic step and the diagnosis should be confirmed by the detection of HSV DNA in CSF by PCR.