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Meningitis is inflammation of the membranes (meninges) covering the brain and the spinal cord. Although the most common causes are infection (either bacterial or viral), chemical agents and even tumor cells may cause meningitis. Encephalitis and brain abscess can complicate infective meningitis.
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.
Non-infectious causes include: -
- Intrathecal drugs
- Lead poisoning
20,000 to 25,000 cases of bacterial meningitis are seen in the United States every year. 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.
Histopathology: 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. Photo at: Atlas of Pathology
The classical symptoms of meningitis are headache, neck stiffness and photophobia (the trio are called "meningism"). An altered level of consciousness or other neurological deficits may be present depending on the severity of the disease. A lumbar puncture to obtain cerebrospinal fluid (CSF) is usually indicated to determine the cause and direct appropriate treatment.
Meningitis is a medical emergency, being a condition with a high mortality rate if untreated. Patients with suspected meningitis should optimally initially have a CT scan to help determine if there is a raised intracranial pressure that might cause a serious or fatal brain herniation during lumbar puncture. If there are no signs of elevated central nervous system pressure demonstrated on the CT scan, a lumbar puncture procedure is performed to obtain cerebrospinal fluid for microscopic examination, chemical analysis, and bacterial cultures. Broad spectrum antibiotics should be urgently started before the culture results are available. 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). When cerebrospinal fluid gram stain, or blood or CSF culture and sensitivity results, are available, 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 ear). These should be investigated when diagnosis of meningitis is confirmed or suspected.
If the patient is commonly in contact with many others (e.g. at school or army barracks), people in the surroundings (and usually family members) may be commenced on prophylactic treatment; this is generally done with the antibiotic rifampicin, which is otherwise mainly used in tuberculosis.
Vaccinations against Haemophilus influenzae (Hib) have decreased neonatal 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.
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