Aseptic meningitis is inflammation of the subarachnoid space (located within the layers of tissue covering the brain and spinal cord) that is diagnosed when standard testing does not detect bacteria.
In aseptic meningitis, the space between middle and inner layers of tissues covering the brain and spinal cord (meninges) is inflamed. This space, called the subarachnoid space, forms a channel for cerebrospinal fluid, which flows over the surface of the brain and spinal cord (see Biology of the Nervous System: Viewing the Brain).
Aseptic meningitis is usually caused by a virus but occasionally has another cause. Unless comprehensive testing is done, the cause is often unidentified.
Some viruses can directly infect the meninges and subarachnoid space around the brain and suddenly cause meningitis. Among the most common are
Infections caused by these viruses can occur in epidemics.
Other viruses directly cause infection that occurs as isolated cases (sporadically). They include the herpes simplex virus, Epstein-Barr virus, human immunodeficiency virus (HIV), varicella-zoster virus (that causes chickenpox), and mumps virus. Mumps is a common cause of meningitis worldwide, but it is uncommon in the United States because vaccination is widespread. In Mollaret's meningitis, aseptic meningitis occurs repeatedly. It is caused by herpes simplex virus type 2, which causes most cases of genital herpes. Viruses that cause encephalitis usually also cause some degree of meningitis.
Sometimes aseptic meningitis is diagnosed when meningitis is caused by bacteria that are hard to identify, such as the bacteria that cause Lyme disease, syphilis, or tuberculosis.
Aseptic meningitis may be caused by the following (see Meningitis: Some Noninfectious Causes of Meningitis):
Meningitis often develops after or at the same time as a flu-like illness or viral infection that causes mild symptoms. These symptoms are often general and may include fever, a general feeling of illness (malaise), cough, muscle aches, and headache.
Usually, aseptic meningitis causes symptoms that are similar to those of bacterial meningitis (fever, headache, vomiting, sluggishness, and a stiff neck). However, people do not become as ill. People may not have a fever, particularly when the cause is not an infection.
Most people recover in 1 to 2 weeks.
When meningitis is suspected, a spinal tap (lumbar puncture) is usually done to obtain a sample of cerebrospinal fluid, and standard tests are done on the fluid. They include determining the number and type of white blood cells in the fluid and growing (culturing) bacteria in the fluid so that they can be identified (see Meningitis: Diagnosis). Doctors diagnose aseptic meningitis when the cerebrospinal fluid contains excess white blood cells (indicating inflammation), but standard tests do not detect any bacteria that could be the cause.
Usually, standard tests do not include culturing viruses, which is technically difficult and may take many days. (An exception is enteroviruses, which can be cultured.) Instead, the polymerase chain reaction (PCR) technique is used to identify viruses (such as herpesviruses and HIV) and to measure levels of antibodies to the virus in cerebrospinal fluid and blood. Antibody levels are measured initially and 3 to 4 weeks later. Then the measurements are compared. If antibody levels increase much more in the cerebrospinal fluid than in the blood, the virus probably caused the meningitis. If the increase in cerebrospinal fluid and blood is about as same, the virus probably infected the body but did not cause the meningitis.
The cause, if identified, is treated. For example, if the bacteria that cause Lyme disease, syphilis, or tuberculosis are identified, antibiotics specific for those bacteria are used. Cancer is treated with surgery, radiation therapy, or chemotherapy, as appropriate. If a drug is the cause, it is stopped or the dose is reduced. Most viral infections are not treated with antiviral drugs and resolve on their own. However, Mollaret's meningitis is treated with acyclovir, and cytomegalovirus infection is treated with ganciclovir.
If doctors suspect aseptic meningitis but cannot rule out bacterial meningitis at the initial examination, several antibiotics are given as if bacterial meningitis were the diagnosis. Doctors do not wait for test results. If tests do not detect any bacteria in the cerebrospinal fluid and if the fluid contains levels of sugar, protein, and white blood cells that suggest aseptic meningitis, antibiotics are stopped.
Regardless of the cause, symptoms are treated. Acetaminophen, given by mouth, and fluids, given by mouth or intravenous injection, can relieve headache and fever.
Last full review/revision May 2008 by Michael Jacewicz, MD