An inflammation of the meninges, most often caused by infection.
Meningitis is a potentially fatal inflammation of the meninges, membranes which encase the brain and spinal cord. Meningitis is most commonly caused by an infection of bacteria, viruses, or fungi, although there can be other causes, including bleeding into the meninges, cancer, or diseases of the immune system. The inflammation causes swelling of the brain, whose fragile tissues are pressed against the skull. Brain cells in these areas can become damaged and eventually die.
The most classic symptoms of meningitis include fever, headache, vomiting, photophobia (extreme sensitivity to light), irritability, lethargy, and a stiff neck. The disease progresses with seizures, confusion, and eventually coma. Infants, however, may not show these signs. A baby's immune system is not yet developed enough to mount a fever in response to infection, so fever may be absent. Some infants with meningitis may have seizures as their only identifiable symptom.
The origin of an infection leading to meningitis varies according to an individual's age, habits, living environment, and health status. In newborns, the most common agents of meningitis are those contracted from the mother, including Group B streptococci, Escherichia coli, and Listeria mono cy to gene s. Older children are more frequently infected by Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae, while adults are infected by S. pneumoniae and N. meningitidis. N. meningitidis is the only organism that can cause epidemics of meningitis. Epidemics of meningitis can occur in crowded conditions, such as when a child in a day care falls ill with N. meningitidis meningitis and exposes other children and workers to the infection.
Viral causes of meningitis include herpes simplex, mumps and measles, chicken pox, rabies, a number
Meningitis can damage the brain in several ways. The agent of infection can damage the brain tissue directly or cause swelling of brain tissue, compressing it against the inner surface of the skull. Swelling of the meninges may interfere with the normal absorption of cerebrospinal fluid by blood vessels, causing accumulation of the fluid and resultant pressure on the brain. Inflammation may reduce the blood-brain barrier's effectiveness in preventing the passage of toxic substances into brain tissue.
The most frequent long-term effects of meningitis include deafness and blindness, due to compression of specific nerves and parts of the brain controlling hearing and sight. Patients can also develop seizures. In addition, scarring of the meninges may result in obstruction of the normal flow of cerebrospinal fluid, causing it to accumulate.
Diagnosis can be verified by certain manipulations of the patient's head; for example, lowering the head (chin toward chest) is very painful for a patient with meningitis. However, the most important diagnostic test is the lumbar puncture (LP), commonly known as the spinal tap. This procedure involves the insertion of a needle into a space between the vertebrae in the lower back, and the withdrawal of a small amount of cerebrospinal fluid. Abnormally low levels of glucose, a normal ingredient of the fluid, indicate bacterial meningitis. Another indicator of meningitis is the presence of white blood cells in the cerebrospinal fluid
Antibiotic medications (forms of penicillins and cephalosporins, for example) are the crucial element of treatment against bacterial meningitis. Because the blood-brain barrier prevents passage of most substances into the brain, medications must be delivered intravenously in very high doses. Antiviral medications are administered in the case of viral meningitis, and antifungal medications are available as well. Other treatments for meningitis involve decreasing inflammation with steroids, and monitoring the balance of fluids, glucose, sodium, potassium, oxygen, and carbon dioxide in the patient's system. Patients who develop seizures also need medications to halt the seizures and prevent their return.
Many cases of meningitis can be prevented. A series of vaccines against Haemophilus influenzae, started at the age of two months, has greatly reduced the incidence of that form of meningitis. Vaccines also exist against Neisseria meningitidis and Streptococcus pneumoniae, but these vaccines are recommended only for individuals who have particular susceptibility to those organisms, due to certain immune deficiencies, lack of a spleen, or sickle-cell anemia. Because N. meningitidis is known to cause epidemics, people who have close contact with a known carrier are treated with Rifampin, which generally stops the spread of the disease. Mothers with certain risk factors may be treated with antibiotics during labor, to prevent the passage of microorganisms (particularly Group B streptococcus) which may cause meningitis in the newborn.
Krugman, Saul, et al. Infectious Diseases of Children. St. Louis: Mosby Year Book, 1992.
Meningitis. Evanston, IL: Altschul Group Corporation, 1996. (One 13-1/2 minute videocassette.)