False-positive results obtained for immunoglobulin M antibody tests of cerebrospinal fluid for herpes simplex virus in a patient with varicella zoster virus encephalitis.

A 66-year-old man presented with a disturbed consciousness and seizure-like movements, followed by the initial symptoms of herpes zoster. Immunoglobulin (Ig) M antibodies to varicella zoster virus (VZV) as well as herpes simplex virus (HSV) were positive in the cerebrospinal fluid (CSF), whereas polymerase chain reaction of the CSF was positive for VZV-DNA but negative for HSV-DNA. The serum/CSF IgM ratio for VZV and HSV increased in association with a clinical improvement. This is a case report of a rare case of VZV encephalitis demonstrating false-positive results for IgM to HSV in the CSF. The increase in the serum/CSF IgM ratio possibly reflects a recovery from blood-brain barrier breakdown.