What is meningitis?

Quick Answer
An inflammation of the meninges of the brain and spinal cord.
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Causes and Symptoms

The meninges is the three-layered covering of the spinal cord and brain. The layers are the outer dura mater, inner pia mater, and middle arachnoid. Meningitis is the inflammation or infection of the arachnoid and pia mater. It is characterized by severe headaches, vomiting, and pain and stiffness in the neck. These symptoms may be preceded by an upper respiratory infection. The age of the patient may affect which signs and symptoms are displayed. Newborns may exhibit either fever or hypothermia, along with lethargy or irritability, disinterest in feeding, and abdominal distension. In infants, examination may find bulging of the fontanelles (the soft areas between the bones of the skull found in newborns). The elderly may show lethargy, confusion, or disorientation. As pressure in the skull increases, nausea and vomiting may occur. With meningococcal meningitis, a rash of pinpoint-sized or larger dots appears.

Most cases of meningitis are the result of bacterial infection. These cases are sometimes referred to as septic meningitis. The bacteria invade the subarachnoid space and may have traveled from another site of infection, having caused pneumonia, cellulitis, or an ear infection. It is unclear if the bacteria make their way from the original area of infection to the meninges by the bloodstream or the lymphatic system. Once they have entered the subarachnoid space, they divide without inhibition since there is no impediment posed by defensive cells. In other words, the cerebrospinal fluid (CSF) contains very few white blood cells to inactivate the bacteria. More rarely, some bacteria may be introduced into the area by neurological damage or surgical invasion.

The most common cause of bacterial meningitis in adults and older children is meningococcus (Neisseria meningitidus). It is a diplococcus that typically does its damage inside the cell. The incidence of meningococcal meningitis is two to three cases per 100,000 people per year, and it most often affects schoolchildren and military recruits. Haemophilus influenzae is the most common culprit infecting babies between two months and one year of age. Complications or residual effects often follow bacterial meningitis. These may include deafness, delayed-onset epilepsy, hydrocephalus, cerebritis, and brain abscess. In addition, for several weeks after resolution of the disease the patient may experience headaches, dizziness, and lethargy.

Aseptic meningitis is meningitis attributable to causes other than bacteria. These causes include neurotropic viruses, such as those that cause poliomyelitis or encephalitis; other viruses such as those that cause mumps, herpes, mononucleosis, hepatitis, chickenpox, and measles; spirochetes; bacterial products from brain abscesses or previous cases of bacterial meningitis; and foreign bodies, such as those found in the air or chemicals, in the CSF. Most cases of aseptic meningitis are viral in origin. The signs and symptoms are similar to those of bacterial meningitis. Onset is usually gradual, with symptoms starting mildly. The slight headache becomes worse over the course of several days, the neck becomes characteristically stiff, and photophobia (dislike of bright light) occurs.

Tuberculous meningitis is different from most other forms of meningitis because it lasts longer, has a higher mortality rate, and affects the CSF less. It mostly strikes children and is usually the result of a bacillus infection from the respiratory tract or the lymphatic system that has relocated to the meninges. When the bacilli are translocated to the central nervous system, they form tubercles that release an exudate. If tuberculous meningitis is left untreated, death may occur within three weeks. Even with treatment, it may result in neurologic abnormalities.

Cryptococcal meningitis is a fungal infection most often caused by Cryptococcus neoformans, a strain of Cryptococcusfungus found in the soil worldwide. Although rare in the United States, it affects one million people around the world each year, causing 625,000 deaths annually. Patients with risk factors for this form of meningits include those with AIDS, cirrhosis, diabetes, leukemia, lymphoma, sarcoidosis, and those who have received organ transplants. Those with weakened immune systems are also more likely to be affected.

Treatment and Therapy

If meningitis is suspected, the first testing procedure is an examination of the CSF. To obtain CSF, a lumbar puncture, sometimes called a spinal tap, is made. Opening pressure, protein and glucose concentrations, total cell count, and cultures of microbes are determined. In cases of meningitis, the CSF is almost always cloudy and generally comes out under higher-than-normal pressure. An elevated white blood cell count in the CSF would be one indication that the patient has bacterial meningitis; another would be lowered serum glucose but slightly raised protein concentration, especially albumin. About 90 percent of bacterial meningitis cases show gram-positive staining. The examination of this slightly atypical fluid, along with presenting symptoms and signs, gives the diagnostician some confidence in diagnosing meningitis accurately. Further cultures and a repeat puncture are necessary to pinpoint the kind of meningitis and to check the effect of the treatment.

Bacterial meningitis should be treated promptly with antibiotics specific for the causative bacteria. The success of treatment is contingent on the magnitude of the bacterial count and the quickness with which the bacteria can be controlled. Virtually all bacterial cases are treated with ampicillin or penicillin. Cases aggressively treated with very large doses of antibiotics are the most successful. If antibiotics do not destroy the areas of infection, surgery should be considered. Surgery is especially effective if meningitis is recurrent or persistent. Viral meningitis may be treated with adenine arabinoside if the cause is herpes simplex. No medication will kill other viruses causing the infection. The condition usually resolves itself in a few days, even without treatment. When necessary, supportive therapy should be employed, including blood transfusions. Young children with open fontanelles often undergo subdural taps to relieve pressure caused by CSF buildup.

Mortality rates in meningitis vary with age and the pathogen responsible. Those suffering from meningococcal meningitis (without overwhelming bacterial numbers) have a fatality rate of only 3 percent. Newborns suffering from gram-negative meningitis, however, have a 70 percent mortality rate. In addition, the younger the patient, the more likely the incidence of lasting neurological damage.

There are two basic ways to prevent meningitis: chemoprophylaxis for likely candidates of the disease and active immunization. Those exposed to a known case are usually treated with rifampin for four days; rifampin is especially useful in inactivating H. influenzae. Active immunization is suggested for toddlers eighteen to twenty-four months of age, especially for those in situations where there is a high risk of exposure (such as day care centers).

A study published in the April 4, 2013, issue of the New England Journal of Medicine found that patients with cryptococcal meningitis who were treated with a combination of amphotericin B and flucytosine had a 40 percent reduced risk of death from the disease than those who were treated with amphotericin B alone.

Bibliography

American Medical Association. American Medical Association Family Medical Guide. 4th rev. ed. Hoboken, N.J.: John Wiley & Sons, 2004.

Bloom, Floyd E., M. Flint Beal, and David J. Kupfer, eds. The Dana Guide to Brain Health. New York: Dana Press, 2006.

Ferreiros, C. Emerging Strategies in the Fight Against Meningitis. New York: Garland Science, 2002.

HealthDay. "Combo Therapy Helps Knock Out Fungal Meningitis." MedlinePlus, April 3, 2013.

McCoy, Krisha. "Bacterial Meningitis (Spinal Meningitis)." Health Library, October 31, 2012.

MedlinePlus. "Meningitis." MedlinePlus, May 13, 2013.

Meningitis Research Foundation. Meningitis Research Foundation: Meningitis & Septicaemia, 2013.

Shmaefsky, Brian. Meningitis. 2d ed. Philadelphia: Chelsea House, 2010.

Tunkel, Allan R. Bacterial Meningitis. Philadelphia: Lippincott Williams & Wilkins, 2001.

Wilson, Michael, Brian Henderson, and Rod McNab. Bacterial Disease Mechanisms: An Introduction to Cellular Microbiology. New York: Cambridge University Press, 2002.

Zieve, David. "Meningitis—Cryptococcal." MedlinePlus, October 7, 2012.

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