Meningitis is a condition wherein the membrane layers that enclose the brain and the spinal cord, collectively known as the meninges, are inflamed. These membrane layers are the pia mater, the arachnoid mater, and the dura mater. Between the delicate pia mater and the loosely fitting arachnoid mater lies the subarachnoid space, a gap filled with cerebrospinal fluid that also serves to protect and cushion the brain and the spinal cord. In many cases of meningitis, the meninges are affected by inflammation because the cerebrospinal fluid has been contaminated by infectious agents. Failure to diagnose meningitis is considered a form of medical negligence.
There are five common classifications of meningitis: viral, bacterial, fungal, parasitic, and non-infectious. The most common type among the five is viral meningitis, which is caused by such viruses as herpes simplex virus, enterovirus, mumps virus, varicella zoster virus, and human immunodeficiency virus. It is a serious infection, but it is rarely fatal and usually far less severe than bacterial meningitis. Full recovery from viral meningitis is very likely for people with normal immune systems.
Bacterial meningitis, on the other hand, is far less common than viral meningitis but is considered a medical emergency as death can result if immediate intervention is not instituted. Bacterial types that can cause meningitis include meningococci, pneumococci, Group B streptococci, E. coli, Haemophilus influenzae, tubercle bacilli, and Listeria strains. Contamination of the cerebrospinal fluid by these infectious agents activates the immune system to launch a large-scale inflammatory response in an attempt to fight off the invasion. Fluid leaks from blood vessels, white blood cells accumulate, and blood vessel walls become inflamed, all leading to an increase in the pressure inside the skull cavity. Because of the increased pressure, blood flow to the brain is diminished and brain cells may suffer a deprivation of oxygen and nutrients, eventually leading to cell death.
Another type of meningitis is fungal, which is caused by agents such as Cryptococcus neoformans and Histoplasma capsulatum. They usually gain entry to the body through the inhalation of fungal spores, and the risk of contacting fungal meningitis increases with diminished immunity due to aging, HIV/AIDS, or use of immunosuppressing drugs.
Parasitic meningitis is very rare especially in developed countries, but is considered fatal. Parasites such as Angiostrongylus cantonensis and Schistosoma species can contaminate food and water, while the amoeba Naegleria fowleri can get inside the body through inhalation.
Non-infectious meningitis occurs not because of the invasion of infectious microorganisms, but of causes such as cancer spreading to the meninges, systemic lupus, certain medications, invasive brain surgery, and head injuries.
Common signs and symptoms that may indicate meningitis include a rapid onset of high fever, severe headache, and neck stiffness. Because of brain affectation, mental status changes may also be observed, such as irritability, lethargy, decreased consciousness, and seizures. The person with meningitis may also be unable to tolerate bright light because of heightened eye sensitivity, a condition known as photophobia. In infants and small children, these symptoms may not be evident, but will instead show general signs of irritability, poor feeding, and looking unwell.
Treatment of meningitis depends on its cause. As mentioned above, bacterial meningitis is a medical emergency and needs immediate intervention, usually involving intravenous antibiotics. Corticosteroids, medications that work to decrease inflammation, are also helpful in regulating the immune response in meningitis.
