Central Nervous System (CNS) Disease

Viruses are the most common infectious agents of encephalitis (inflammation of the brain) in humans and more than 100 causative viruses are known followed by bacterial, parasitic, fungal and prion agents. Non-infectious causes of encephalitis include autoimmune, neoplastic, metabolic and other disorders. Still, in more than half of all cases of encephalitis the aetiology remains unknown. Encephalitis is not a
common disease, but because early start of specific therapy may prevent serious and lasting damage to the brain, early and correct identification of the infectious agent may make a dramatic difference to each patient.
Amplification of nucleic acids from cerebrospinal fluid (CSF) obtained by lumbar puncture represents a diagnostic breakthrough. It may be difficult to distinguish early symptoms of encephalitis from meningitis and meningoencephalitis most commonly caused by enteroviruses.When only an enterovirus is present in the CSF, the prognosis is usually good without specific treatment. In contrast, when a member of the herpes virus family infects the brain, early antiviral (acyclovir or gancyclovir) treatment is very important to avoid lasting damage to the brain or even death. In particular HSV-1, but also HSV-2 and VZV, accounts for a large proportion of cases with infectious encephalitis and may occur in young and otherwise healthy people. Cytomegalovirus (CMV) infection of the CNS is more commonly associated with immune suppression, immune deficiency such as AIDS or congenital CMV infection. Human herpes virus 6 (HHV-6) is associated with febrile convulsions in small children and may also cause encephalitis. EBV is associated with both encephalitis and lymphomas in the brain. The very high sensitivity and specificity of real-time qPCR assays for the detection of these agents are well documented as soon as symptoms and clinical signs are apparent.For therapeutic reasons, it is initially important to distinguish cases of Mycobacterium tuberculosis, Mycoplasma pneumoniae and Borrelia burgdorferi (the cause of Lyme’s disease) and pyogenic bacteria. A combination of biochemical and microscopic examination of the CSF, together with cultivation and PCR, are useful in these cases. Immunocompromised patients, newborn and recent stays in tropical or endemic areas suggest specific diagnostic procedures in connection with CNS disease.