[Virological diagnostics in acute encephalitis. Experience with nucleic acid detection and ratio examination during the period 1991-94].

: In every single case of acute encephalitis it is important to confirm the clinical diagnosis by means of virological investigations. Previously, examination by brain biopsy was regarded as the gold standard for detecting the presence of virus or virus antigen in suspected cases of encephalitis caused by herpes simplex virus, but the extraction of the sample material requires experience, and is not without risk. In recent years, detection of herpes simplex DNA using the polymerase chain reaction is recommended as the method of choice during the acute state of the illness, followed by ratio determination, e.g. the relation between IgG antibodies in serum and cerebrospinal fluid during the reconvalescence period. Between 1991 and 1994, the clinical diagnosis of acute encephalitis was confirmed by laboratory investigations in 42 cases in our laboratory. Detection of viral DNA and subsequent ratio determination showed the encephalitis to have been caused by herpes simplex virus in 21 cases, and by varicella zoster virus in eight cases. Nucleic acid was detected in 21 cases, and 16 patients showed pathological ratio values. These results show that the polymerase chain reaction is a valuable diagnostic tool during the first two weeks of the illness, whereas ratio determination is a better way of investigating samples taken after this period.