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Pathology => Human Diseases => Meningitis
Meningitis
INTRODUCTION
Meningitis, inflammation of the meninges, the membranes that surround the brain and spinal cord. Meningitis may be caused by a physical injury, a reaction to certain drugs, or more commonly, infection by certain viruses, bacteria, fungi, or parasites. This article focuses on meningitis caused by viral or bacterial infection. Viral meningitis, the most common form of the disease, affects at least 9,000 people in the United States each year. The actual number of cases is probably much higher, since the condition often goes undiagnosed. An estimated 6,500 cases of bacterial meningitis, the most serious form of the disease, occur in the United States each year. Most cases of infectious meningitis occur in the first five years of life.
CAUSE
The most common causes of viral meningitis are coxsackie viruses and echoviruses, although herpes viruses, the mumps virus, and many other viruses can also cause the disease. Viral meningitis is rarely fatal, and most patients recover from the disease completely.
Most cases of bacterial meningitis are caused by one of three species of bacteria-Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis. Many other bacteria, including Escherichia coli and the bacteria that are responsible for tuberculosis and syphilis, can also cause the disease. Bacterial meningitis can be fatal if not treated promptly. Some children who survive the infection are left with permanent neurological impairments, such as hearing loss or learning disabilities.
Many of the microorganisms that cause meningitis are quite common in the environment and are usually harmless. The microorganisms typically enter the body through the respiratory system or, sometimes, through the middle ear or nasal sinuses. Many people carry these bacteria or viruses without having any symptoms at all, while others experience minor, coldlike symptoms. Meningitis only develops if these microorganisms enter a patient's bloodstream and then the cerebrospinal fluid (CSF), which surrounds the brain and spinal cord. The CSF contains no protective white blood cells to fight infection, so once the microorganisms enter the CSF, they multiply rapidly and make a person sick.
Although the viruses and bacteria that cause meningitis are contagious, not everyone who comes in contact with someone with meningitis will develop the disease. In fact, meningitis typically occurs in isolated cases. Occasionally outbreaks of meningitis caused by Neisseria meningitidis, also known as meningococcal meningitis, occur in group living situations, such as day-care centers, college dormitories, or military barracks. A child whose immune system is weakened-due to a disease or genetic disorder, for instance-is at increased risk for developing meningitis. In general, however, scientists do not know why microorganisms that are usually harmless are able to cross into the CSF and cause meningitis in some people but not others.
SYMPTOMS AND DIAGNOSIS
No matter what the cause, the symptoms of meningitis are always similar and usually develop rapidly, often over the course of a few hours. Nearly all patients with meningitis experience vomiting, high fever, and a stiff neck. Meningitis may also cause severe headache, back pain, muscle aches, sensitivity of the eyes to light, drowsiness, confusion, and even loss of consciousness. Some children have convulsions. In infants, the symptoms of meningitis are often more difficult to detect and may include irritability, lethargy, and loss of appetite. Most patients with meningococcal meningitis develop a rash of red, pinprick spots on the skin. The spots do not turn white when pressed, and they quickly grow to look like purple bruises.
Meningitis is diagnosed by a lumbar puncture, or spinal tap, in which a doctor inserts a needle into the lower back to obtain a sample of CSF. The fluid is then tested for the presence of bacteria and other cells, as well as certain chemical changes that are characteristic of meningitis.
TREATMENT AND PREVENTION
It is imperative to seek immediate medical attention if the symptoms of meningitis develop in order to determine whether the meningitis is viral or bacterial. Any delays in treating bacterial meningitis can lead to stroke, severe brain damage, and even death. Patients with bacterial meningitis are usually hospitalized and given large doses of intravenous antibiotics. The specific antibiotic used depends on the bacterium responsible for the infection. Antibiotic therapy is very effective, and if treatment begins in time, the risk of dying from bacterial meningitis today is less than 15 percent.
No specific treatment is available for viral meningitis. With bed rest,
plenty of fluids, and medicine to reduce fever and control headache, most patients recover from viral meningitis within a week or two and suffer no lasting effects.
Good hygiene to prevent the spread of viruses is the only method of preventing viral meningitis. To help prevent the spread of bacterial meningitis, antibiotics are sometimes given to family members and other people who have had close contact with patients who develop the disease. Vaccines are also available against some of the bacteria that can cause meningitis. A vaccine against one strain of Haemophilus influenzae, once the most common cause of bacterial meningitis, was introduced during the 1980s and has been a part of routine childhood immunization in the United States since 1990. This vaccine has dramatically reduced the number of cases of bacterial meningitis. Vaccines also exist for certain strains of Neisseria meningitidis and Streptococcus pneumoniae but are not a part of routine immunization. The Neisseria meningitidis vaccine is given to military recruits and people who are planning travel to areas of the world where outbreaks of meningococcal meningitis are common. The Streptococcus pneumoniae vaccine is recommended for people over age 65.
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