Meningitis overview

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Meningitis is the inflammation of the protective membranes covering the central nervous system, known collectively as the meninges (the leptomeninges and underlying subarachnoid cerebrospinal fluid).^[1] Meningitis may develop in response to a number of causes, including infectious agents (bacteria, viruses, fungi, or other organisms), physical injury, cancer, or certain drugs. While some forms of meningitis are mild and resolve on their own, meningitis is a potentially serious condition owing to the proximity of the inflammation to the brain and spinal cord. The potential for serious neurologic damage or even death necessitates prompt medical attention and evaluation. Infectious meningitis, the most common form, is typically treated with antibiotics and close observation. ^{[2] [3] [4] [5] [6] [7]}

Most cases of meningitis are caused by microorganisms, such as viruses, bacteria, fungi, or parasites, that spread into the blood and into the cerebrospinal fluid (CSF).^[8] Non-infectious causes include cancers, systemic lupus erythematosus and certain drugs. The most common cause of meningitis is viral, and often runs its course within a few days. Bacterial meningitis is the second most frequent type and can be serious and life-threatening. Numerous microorganisms may cause bacterial meningitis, but Neisseria meningitidis ("meningococcus") and Streptococcus pneumoniae ("pneumococcus") are the most common pathogens in patients without immune deficiency, with meningococcal disease being more common in children. Staphylococcus aureus may complicate neurosurgical operations, and Listeria monocytogenes is associated with poor nutritional state and alcoholicism. Haemophilus influenzae (type B) incidence has been much reduced by immunization in many countries. Mycobacterium tuberculosis (the causative agent of tuberculosis) rarely causes meningitis in Western countries but is common and feared in countries where tuberculosis is endemic.

From its recognition in 1805 until the early 20th century, bacterial meningitis was virtually uniformly fatal. Until recent years, up to 50% of patients who survived the acute infection would be left with permanent sequelae such as mental retardation and hearing loss. Over the past several years, there has been a striking shift in the demography of meningitis.

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