Unusual course of herpes simplex virus encephalitis after acyclovir therapy

This is a report on a case of herpes simplex encephalitis (HSE) taking an unusual course after initially successful acyclovir therapy. The etiology of HSE was proven serologically, by repeated detection of herpes simplex virus (HSV)-specific DNA sequences in cerebrospinal fluid (CSF) with polymerase chain reaction (PCR) and was supported by cerebral imaging. After both the neurological symptoms and laboratory findings had improved initially under acyclovir therapy, the patient's clinical condition deteriorated accompanied by a renewed increase in CSF pleocytosis and protein content. Nuclear magnetic resonance (NMR) imaging confirmed the finding of bilateral, mainly temporal lesions compatible with a diagnosis of relapsing HSE. The patient responded well to a second cycle of antiviral therapy but required a third treatment cycle due to renewed deterioration later on. HSV-specific DNA sequences could not be demonstrated in several consecutive CSF samples taken after the first week of illness but increased inflammatory changes typical of HSE were seen on NMR during phases of deterioration. IgM-class antibodies against HSV were detected in CSF 4 weeks after onset of symptoms and stayed positive for at least 7 weeks. Reasons for the repeated deterioration and possible explanations for the absence of HSV DNA in spite of what could be seen as relapses are discussed.