Differential diagnosis

Conditions from which viral meningitis must be differentiated are: the early stages of (or partially treated) bacterial meningitis; some cases of subarachnoid haemorrhage; other causes of aseptic meningitis caused by fastidious bacteria, fungi, and parasites that do not grow readily in routine culture; parameningeal infection, inflammation, or neoplasia; and collagen/vasculitic disease. To confirm the diagnosis, CSF examination is mandatory. If there are neurological signs suggestive of raised ICP then appropriate imaging (see below) should be undertaken first. CSF pressure is normal or slightly raised and the fluid is clear to the naked eye. White cell counts are in the range of up to 500-1000/mm3, mainly lymphocytes although, in some, polymorphs may predominate. In such cases it is prudent to re-examine the CSF 12 hours later to identify a developing lymphocytosis and exclude a bacterial cause.5 CSF protein may be slightly raised, glucose is normal or only slightly reduced. Numerous laboratory tests have been applied to CSF with the claim that they differentiate a bacterial from a viral aetiology, but none has sufficient discrimination to be useful. A similar lack of specificity attaches to the occasional abnormalities, which may be seen in blood counts, blood biochemistry, and the EEG.

In most cases it is not necessary to establish an exact aetiology for treatment purposes, as the disease is benign and self-limiting. To establish the aetiology, the virus may be isolated from CSF or by serological studies of acute and convalescent serum samples, identification of IgM antibody, or viral antigen in CSF. The use of PCR for amplification of viral nucleic acid within CSF has revolutionised the diagnosis of viral infections of the central nervous system.6,7

Provided other similar treatable disorders have been excluded, symptomatic treatment with analgesics and antiemetics is all that is required. Antibiotics should not be given. Pleconaril is a novel antiviral agent that integrates into the "pocket" on the surface of the enteroviral capsid into which the cellular receptor normally fits and thus inhibits viral attachment to host cells and uncoating.8 It has been shown in randomised, placebo controlled trials to be safe and effective in the treatment of enteroviral meningitis in children, adolescents, and adults. It will probably also be useful in the treatment of life threatening and chronic enteroviral meningoencephalitis.9

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