meningitis

—meningitic /men'in jit"ik/, adj.

/men'in juy"tis/, n. Pathol.

inflammation of the meninges, esp. of the pia mater and arachnoid, caused by a bacterial or viral infection and characterized by high fever, severe headache, and stiff neck or back muscles.

[1820-30; < NL; see MENINGES, -ITIS]

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Inflammation of the meninges.

Bacteria (including meningococcus, among others), often from infection elsewhere, produce the most dangerous forms. Symptoms develop rapidly: vomiting, then severe bursting headache, then stiff neck. Young children may have convulsions. The patient may die within hours. Pus in cerebrospinal fluid can block brain passages and spinal spaces, leading to life-threatening hydrocephalus. Speedy diagnosis (by lumbar puncture) and treatment (with antibiotics) can prevent brain damage and death. Viral meningitis usually has a short course and requires no therapy.

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▪ pathology

      inflammation of the meninges, the membranes covering the brain and spinal cord. Meningitis can be caused by various infectious agents, including viruses, fungi, and protozoa, but bacteria produce the most life-threatening forms. The patient usually experiences fever, headache, vomiting, irritability, anorexia, and stiffness in the neck.

      Among the bacteria that can cause meningitis are the meningococcus (Neisseria meningitidis), Haemophilus influenzae, and various strains of pneumococci (pneumococcus), streptococci (Streptococcus), or staphylococci (staphylococcus). A bacterial infection elsewhere in the body may be carried to the meninges through the bloodstream itself or from an adjacent infected organ, such as the middle ear or the nasal sinuses. The infectious agents multiply in the meninges, where they produce a pus that thickens the cerebrospinal fluid, thereby causing various symptoms and complications such as seizures, deafness, blindness, paralysis, and various degrees of impairment of the intellect.

      Bacterial meningitis usually has three main stages. At first, the bacteria multiply in the nasal passages and throat, often causing no painful symptoms. Next, they invade the blood, introducing toxic substances into the circulation and causing fever; if the infection is caused by N. meningitidis, a rash may appear and develop into hemorrhagic spots (petechiae and purpura) in severe cases. In the third stage, the bacteria multiply in the meninges, where they produce intense inflammatory changes and an exudate of pus.

      A characteristic of meningitis is the rapid onset of symptoms, which may result in death within only a few hours. The first symptom of meningitis is usually vomiting. A severe bursting headache develops when the meninges have become inflamed and the pressure of the cerebrospinal fluid has increased. Stiffness of the neck then develops, due to irritation of the spinal nerves supplying those muscles. Deep tendon reflexes are exaggerated, and convulsions may occur in infants and small children. In more severe cases, the cerebrospinal fluid becomes so thickened by pus that the passages between the ventricles (cavities) of the brain and the spaces in the spinal meninges become blocked, causing fluid to accumulate. The accumulation of fluid in the ventricles may in turn result in hydrocephalus, which causes coma and death unless relieved.

      The term meningitis is often applied to meningococcal meningitis, which is caused by N. meningitidis. Epidemics (epidemic) of this disease occurred at irregular intervals, with death occurring in 40–50 percent of cases, until the use of antibiotic drugs greatly reduced both mortality rates and the incidence of the disease; however, severe epidemics are still seen in parts of Africa. Meningococcal meningitis is worldwide in distribution and more likely to occur in cold weather. It is primarily a disease of youth and especially of children (childhood disease and disorder) under age 10, though all ages may be affected. The disease is usually acquired by nasal droplet transmission. vaccines against some types of N. meningitidis are available. Another serious cause of meningitis is H. influenzae; it occurs in infants and young children but only rarely in older persons, and its course and symptoms resemble those of N. meningitidis. The bacterium Streptococcus pneumoniae (pneumococcus) is a common cause of meningitis in adults. In many developing countries, tuberculous meningitis is common.

      Diagnosis of meningitis is made by examination and confirmed by the performance of a test called a spinal tap (or lumbar puncture). In this test a needle is inserted into the lower part of the patient's back between two vertebrae (bones of the spinal column) and a small sample of cerebrospinal fluid is removed. If a bacterial, tuberculous, or fungal infection is found, patients will need intensive medical care; appropriate antibiotics must be administered as soon as meningitis is suspected. The mortality and morbidity of the bacterial disease are substantial, even with the prompt use of appropriate antibiotic therapy.

      The early diagnosis and prompt treatment of meningitis is particularly important in preventing possible permanent damage to the brain, especially in affected children. Meningococcal meningitis is best treated with penicillin. Cases caused by H. influenzae are treated with ampicillin or chloramphenicol. These drugs have reduced mortality rates from bacterial meningitis to less than 5 percent in some areas. A vaccine that gives protection against the type b strain of H. influenzae became commercially available in the 1980s and has proved effective in safeguarding infants and children from the disease. To control the spread of meningitis caused by H. influenzae or N. meningitis, the antibiotic derivative rifampin should be administered to any who have come in contact with the disease.

      Various other forms of meningitis are caused by viruses and ordinarily have a short, uncomplicated, self-limited course that does not require specific therapy. Patients usually recover in three to five days, typically without any serious result.

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