Meningitis is inflammation of the membranes (meninges) covering the brain and the spinal cord. Although the most common causes are infection (bacterial, viral, fungal or parasitic), chemical agents and even tumor cells may cause meningitis. Encephalitis and brain abscess can complicate infective meningitis.

Features

The classical symptoms of meningitis are headache, neck stiffness and photophobia (the trio are called "meningism"). Fever and chills are often present, along with myalgia. An altered state of consciousness or other neurological deficits may be present depending on the severity of the disease. In meningococcal meningitis or septicaemia, a petechial rash may appear. A lumbar puncture to obtain cerebrospinal fluid (CSF) is usually indicated to determine the cause and direct appropriate treatment.

Convulsions are a known complication of meningitis and are treated with appropriate anti-seizure drugs such as phenytoin.

Diagnosis

Most important in the diagnosis of meningitis is examination of the cerebrospinal fluid. A lumbar puncture should be performed promptly whenever the diagnosis of meningitis is suspected. The opening pressure is recorded and the cerebrospinal fluid sample is taken for microscopic examination (complete blood count with differential), chemical analysis (glucose and protein) and microbiology (gram staining and bacterial cultures).

In patients with focal neurological deficits or signs of increased intracranial pressure, a CT scan of the head should be obtained to help determine if there is a raised intracranial pressure that might cause a serious or fatal brain herniation during lumbar puncture. In the absence of these signs, a CT scan is unnecessary and should not delay lumbar puncture and initiation of antibiotic therapy.

Pathology

Purulent (suppurative) leptomeningitis is a diffuse purulent inflammation. The leptomeninges (arachnoida and piamater) contain purulent exudate (pus): leukocytes (neutrophils), fibrin, germs, proteins, necrotic debris. Blood vessels in the subarachnoidian space and those intracerebral are congested and neutrophil margination is present[1].

Causes

Viruses are the most common cause of meningitis.

Major bacteria that cause meningitis are Neisseria meningitidis (meningococcus), Streptococcus pneumoniae (pneumococcus), and Haemophilus influenzae. Less-common bacterial causes include Listeria monocytogenes, Staphylococcus and Escherichia coli. In developing countries, Mycobacterium tuberculosis is a common cause of bacterial meningitis.

Streptococcus agalactiae is an important cause of neonatal meningitis associated with a high mortality rate.

In immunocompromised patients, fungal meningitis may occur, typically caused by Cryptococcus neoformans.

Non-infectious causes include:

• Tumors
  • Leukemia
  • Lymphoma
  • Brain tumors
  • Cerebral metastasis
• Sarcoidosis
• Drugs
  • Intrathecal drugs
    • Methotrexate
• Lead poisoning

Treatment

Meningitis has a high mortality rate if it goes untreated and is thus a severe medical emergency. All suspected cases, however mild, need emergency medical attention. Broad spectrum antibiotics should be started even before the culture results are available, on the presumption that all cases are bacterial in nature, until otherwise proven. If lumbar puncture can not be performed because of raised intracranial pressure (likely due to edema or concomitant brain abscess), a broad spectrum intravenous antibiotic should be started immediately (this is often a third generation cephalosporin or, in less affluent countries, chloramphenicol). When cerebrospinal fluid gram stain, or blood or CSF culture and sensitivity results, are available and confirm the bacterial nature of the infection, then the empiric treatment can be refined by switching to more specific antibiotics. In children (but not in adults) the administration of steroids helps reduce the incidence of deafness following meningitis.

Infection of the meninges usually originates through spread from infection of the neighbouring structures (which include the sinuses and mastoid cells of the ear). These should be investigated when diagnosis of meningitis is confirmed or suspected.

If the patient is commonly in contact with many others (for example at school or in army barracks), people in the surroundings (and usually family members) may be started on prophylactic treatment; this is generally done with the antibiotic rifampicin, which is otherwise mainly used in tuberculosis. Alternative drugs used for prophylaxis include ciprofloxacin and ceftriaxone. Ceftriaxone is the preferred agent for prophylaxis in pregnant women. If there is a risk of neonatal meningitis caused by Streptococcus agalactiae (Group B Streptococcus), then ampicillin, penicillin G, or clindamycin may be used during childbirth.

Vaccination

Vaccinations against Haemophilus influenzae (Hib) have decreased early childhood meningitis significantly.

Vaccines against type A and C Neisseria meningitidis, the kind that causes most disease in preschool children and teenagers in the United States have also been around for a while. Type A also prevalent in sub-Sahara Africa and W135 outbreaks have affected those on Hajj pilgrimage to Mecca.

A vaccine called (MeNZB) for a specific strain of type B Neisseria meningitidis prevalent in New Zealand has completed trials and is being given to everyone in the country under the age of 20. There is also a vaccine, MenBVac, for the specific strain of type B meningoccocal disease prevalent in Norway, and another specific vaccine for the strain prevalent in Cuba.

Epidemiology

Western World

20,000 to 25,000 cases of bacterial meningitis are seen in the United States every year. In developing countries, the incidence is probably higher. Mostly adults are infected, where it can be community acquired or nosocomial. Vaccination against Haemophilus influenzae has reduced the incidence in children.

Meningitis may occur in outbreaks in communities who have close contact with each other, such as in dorms or military establishments. In the large majority of such outbreaks, neisseria meningitidis is the etiologic agent.

The African Meningitis Belt

The "Meningitis Belt" is an area in sub-Saharan Africa which stretches from Senegal in the west to Ethiopia in the east in which large epidemics of meningococcal meningitis occur. It contains an estimated total population of 300 million people. The largest epidemic outbreak was in 1996, when over 250,000 cases occurred and 25,000 people died as a consequence of the disease.

History

In the 19th Century meningitis was a scourge of the Japanese Imperial family, playing the largest role in the horrendous pre-maturity death rate the family endured. In the mid-1800s, only the Emperor Komei and two of his siblings reached maturity out of fifteen total children surviving birth. Komei's son, the Emperor Meiji, was one of two survivors out of Komei's six children, including an elder brother of Meiji who would have taken the throne had he lived to maturity. Five of Meiji's fifteen children survived, including only his third son, the Taisho Emperor, who was feeble-minded, perhaps as a result of having contracted meningitis himself. By Emperor Hirohito's generation the family was receiving modern medical attention. As the focal point of tradition in Japan, during the Tokugawa Shogunate the family was denied modern "Dutch" medical treatment then in use among the upper caste; despite extensive modernization during the Meiji Restoration the Emperor insisted on traditional medical care for his children. The inbreeding produced among the very few families considered worthy of marriage into the imperial line, most of whom were descendents from that same line and therefore none too distant cousins of one another, also played an important role.

See also

• Bacterial meningitis
• Aseptic meningitis
  • Fungal meningitis
  • Parasitic meningitis
  • Drug-induced aseptic meningitis

External links

• Merck Manual: Central nervous system infections
• WHO: Meningococcal meningitis
• CDC: Meningococcal diseaseda:Meningitis

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