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The most common symptoms of meningitis are headache and neck stiffness associated with fever, confusion or altered consciousness, and an inability to tolerate bright light (photophobia) or loud noises (phonophobia). Sometimes, especially in small children, only nonspecific symptoms may be present, such as irritability and drowsiness. If a rash is present, it may indicate a particular cause of meningitis; for instance, meningitis caused by meningococcus bacteria may be accompanied by a characteristic rash.
Meningitis is diagnosed using a technique called lumbar puncture, which involves inserting a needle into the spinal column to extract a sample of cerebrospinal fluid, the fluid that envelops the brain and spinal cord. Meningitis must be treated promptly with antibiotics and sometimes antiviral drugs. In some situations, corticosteroid drugs can also be used to prevent complications from overactive inflammation. Meningitis can lead to serious long-term consequences such as deafness, epilepsy, hydrocephalus and cognitive deficit, especially if not treated quickly. Some forms of meningitis (such as those associated with meningococcus, Haemophilus influenzae type B, pneumococcus or mumps virus infections) may be prevented by immunization.
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It is almost always caused by an infection, usually by a bacteria (bacterial meningitis) or a virus (viral meningitis). In rare cases it can be triggered by a fungus or parasite.
Meningitis occurs most commonly in young children under 5, those aged 17-25 (who often live in close quarters like dormitories and barracks), and people over age 55. People with compromised immune systems, such as people with HIV or AIDS, are also at increased risk.
The meninges are composed of three layers of membranes enclosing the brain and spinal cord.
- Pia mater is the in nermost layer. It is akin to a tissue paper that closely adheres to the brain and spinal cord, dipping into the various folds and crevices.
- Arachnoid mater is the middle layer. It is a filmy membrane that is joined to the pia mater by fine threads resembling a cobweb.
- The dura mater, a parchment-like membrane, lies on the outermost part of the meninges and adheres to the skull and spinal canal.
- The
cerebral spinal fluid (CSF) is the fluid that circulates in the spaces in and around the brain and spinal cord.
The most frequent cause of meningitis is the entry of a microorganism-such as a bacterium or a virus-from an infection elsewhere in the body. The microorganisms travel through the blood and into the meninges and cerebral spinal fluid.
In the bloodstream, infe
ction-causing microorganisms are fought off by white blood cells, an important part of the immune system. However, there are no white blood cells in the cerebral spinal fluid to fight infectious agents.
Once infectious organisms have entered the cerebrospinal fluid, the body's defenses cannot control their rapid growth and the disease races through the delicate surfaces and fluids of the central nervous system.
As the immune system gears up to fight off the microorganisms, it sends out chemical signals that produce inflammation and interfere with the normal functioning of the central nervous system. That, in turn, causes swelling and increased pressure inside the skull, and disrupts the brain's normal functioning.
Facts about meningitis
- The incidence of bacterial meningitis is down 55 percent from 10 years ago.
- There were approximately 13,000 cases of meningitis reported to the U.S. Centers for Disease Control and Prevention in 1994. This is considered a low figure since mild cases of viral meningitis are unlikely to be reported. It is estimated that about 6,000 cases of bacterial meningitis occur in the U.S. each year.
- Approximately 70 percent of meningitis cases occur in the first 5 years of life.
- The vaccine against haemophilus influenze (Hib) has reduced Hib meningitis cases by 95 percent since 1985.