Viral meningitis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Ahmed Elsaiey, MBBCH [2]
Overview
Aseptic meningitis is a condition in which the layers lining of the brain, or meninges, become inflamed and a pyogenic bacterial source is not to blame. Meningitis is diagnosed on a history of characteristic symptoms and certain examination findings (e.g. Kernig's sign). Investigations should show an increase in the number of leukocytes present in the cerebrospinal fluid (CSF), obtained via lumbar puncture, (normal being fewer than five visible per microscopic high power field).
The term aseptic is frequently a misnomer, implying a lack of infection. On the contrary, many cases of aseptic meningitis represent infection with viruses or mycobacteria that cannot be detected with routine methods. While the advent of polymerase chain reaction has increased the ability of clinicians to detect viruses such as enterovirus, cytomegalovirus, and herpes virus in the CSF, many viruses can still escape detection. Additionally, mycobacteria frequently require special stains and culture methods that make their detection difficult. When CSF findings are consistent with meningitis, and microbiologic testing is unrevealing, clinicians typically assign the diagnosis of aseptic meningitis—making it a relative diagnosis of exclusion.
Aseptic meningitis can result from non-infectious causes; it is a relatively infrequent side effect of medications, and can be an early finding in autoimmune disease.
Historical Perspective
Wallgren coined the term aseptic meningitis in 1925 and defined it as a disease with acute onset that had typical systematic symptoms of meningeal involvement, in association with a cerebrospinal fluid (CSF) typical of meningitis (typically with a mononuclear cell predominance). Additionally, there was absence of bacteria on stain and culture and there was no identifiable parameningeal infection.
Classification
There is no formal classification system. It is usually by the causative organism if identified.
Causes
The causes of aseptic meningitis may be infectious or non-infectious.
Risk Factors
The viruses that cause viral meningitis are contagious. Enteroviruses, for example, are very common during the summer and early fall, and many people are exposed to them. However, most infected persons either have no symptoms or develop only a cold or rash with low-grade fever. Only a small proportion of infected persons actually develop meningitis. Therefore, if you are around someone who has viral meningitis, you have a moderate chance of becoming infected, but a very small chance of developing meningitis.
Natural History, Complications and Prognosis
Patients typically had a relatively short and benign course. Other terms sometimes included in the umbrella ‘aseptic meningitis’ (AM) are lymphocytic, viral, chemical, non-bacterial and sterile. Currently, the term AM is used to describe patients with no detectable bacterial cause after initial CSF evaluation. Unfortunately, it is often difficult to predict who will have a life-threatening disease from those who will rapidly recover without specific treatment.
Medical Therapy
Treatment is needed for fungal or mycobacterial causes of aseptic meningitis. Herpesvirus or varicella (chickenpox) virus may be treated with antiviral medicines. Treatment for noninfectious causes consists of pain medications and managing complications, if they occur. No specific treatment is available for enteroviral or most other viral forms of aseptic meningitis.