Meningitis

Definition

Meningitis is an infection or inflammation of the membranes (ie, the meninges ) surrounding the brain and spinal cord.

Etiology

Meningitis is most often caused by a bacterial or viral infection. It also may be caused by a fungal infection, a reaction to certain medications or medical treatments, an inflammatory disease such as systemic lupus erythematosus, some types of cancer, or a traumatic injury to the head or spine.

Bacterial Meningitis

Bacterial meningitis is a rare but potentially fatal disease. It can be caused by several types of bacteria that first cause an upper respiratory tract infection and then travel through the bloodstream to the brain. The disease can also occur when certain bacteria invade the meninges directly. The disease can obstruct blood vessels in the brain, causing stroke and permanent brain damage.

Pneumococcal meningitis is the most common form of meningitis and is the most serious form of bacterial meningitis, with about 6,000 cases reported in the United States each year. The disease is caused by the bacterium S pneumoniae. Pneumococcal meningitis may result in neurologic damage ranging from deafness to severe brain damage.

Meningococcal meningitis, which is caused by the bacterium N meningitides, is common in children aged 2 to 18 years, with about 2,600 persons affected annually in the United States. High-risk groups include infants, persons with suppressed immune systems, travelers to foreign countries where the disease is endemic, and college students (freshmen in particular) who reside in dormitories. Between 10% and 15% of cases are fatal, with another 10% to 15% of cases resulting in brain damage and other serious adverse effects.

Haemophilus meningitis was at one time the most common form of bacterial meningitis, but the number of cases in the United States has been greatly reduced since the introduction of the Haemophilus influenzae b vaccine (Hib). In patients who do have this form of meningitis, 3% to 6% of cases are fatal and up to 20% of surviving patients have permanent hearing loss or other long-term sequelae.

Other forms of bacterial meningitis include Listeria monocytogenes meningitis, which can cross the placental barrier and cause stillbirth or early infant demise; Escherichia coli meningitis, which is most common in older adults and newborns and may be transmitted to an infant through the birth canal; and Mycobacterium tuberculosis meningitis, a rare disease that occurs when the bacterium that causes tuberculosis infects the meninges.

Viral Meningitis

Viral meningitis, also known as aseptic meningitis, is the most common form of meningitis in the United States. Usually, the symptoms of viral meningitis last from 7 to 10 days, and complete recovery is likely. This typically mild disease is usually caused by enteroviruses, such as coxsackieviruses and echoviruses.

Fungal Meningitis

Many fungal infections can affect the brain. The most common form of fungal meningitis is caused by Cryptococcus neoformans, a fungus mainly found in dirt and bird droppings. Cryptococcal meningitis is common in patients with human immunodeficiency virus (HIV) infection. Although treatable, fungal meningitis often recurs in nearly half of affected persons.

Neoplastic Meningitis

Neoplastic meningitis is a condition in which cancer cells spread into the meninges. The condition is often a result of a metastatic process.

Risk Factors

Persons with compromised immune systems, including those persons with HIV infection or those receiving immunosuppressant drugs, are at the highest risk of contracting meningitis. Younger children and children who do not have access to childhood vaccines are also be at increased risk of meningitis.