APH 1999, 57, 263-274:

Role of the virology laboratory in the diagnosis of central nervous system infections.

C. Liesnard

Keywords: aseptic meningitis, meningoencephalitis, enterovirus, PCR

Viral infections of the central nervous system (CNS) have two major clinical presentations: `aseptic' meningitis and meningoencephalitis. Other manifestations like cerebellar ataxia, myelitis, cranial and peripheral nerve palsies, post-infectious syndromes are far less frequent. Enteroviruses are the leading cause of viral CNS infections, with mumps, herpesviruses, HIV, measles, rubella, ... being responsible for a minor part of these infections. As antiviral therapy is available and efficient on some of these infections, rapid diagnosis of viral CNS involvement has become an important goal of the virology laboratory. Conventional techniques have been disappointing, lacking sensitivity and/or rapidity. The most promising recent development in rapid detection of viruses in the CNS has been the application of molecular amplification methods on cerebrospinal fluid (CSF). Among these, polymerase chain reaction (PCR) is the most popular assay. Experience with PCR in the diagnosis of viral CNS is now growing. Various studies have demonstrated the good performances of PCR in terms of sensitivity and specificity and its superiority compared to conventional techniques in the diagnosis of herpes simplex encephalitis, enterovirus meningitis, cytomegalovirus-related neurological diseases in immunosuppressed patients, ... Application of PCR in CNS syndrome without clear etiology like Mollaret's meningitis or in pathology usually diagnosed by brain biopsy like progressive multifocal leucoencephalitis has allowed the detection of implicated viruses (H.S.V and J.C. virus) directly in CSF samples.  Although application of PCR in the diagnosis of viral infections of the CNS appears very promising, some important problems remain unresolved. Assessment of the accuracy of PCR in CSF should compare PCR results with a gold-standard test. However, standard techniques are insensitive (culture), late (intrathecal specific antibody production) or invasive (brain biopsy). Clinical criteria alone are not able to discriminate between CNS infections of various etiologies. Accuracy of PCR in the diagnosis of viral CNS infections must be established by comparison with a body of clinical, neurological, biological investigations. The virology laboratory can play an important role not only in the diagnosis but also in the management of CNS infections, provided that information exchanges and communication between physicians and the laboratory are established.