Meningitis is an inflammation of the brain and spinal cord membranes (meninges). The meninges are the three membranes that cover the brain and spinal cord. It can occur when fluid surrounding the meninges becomes infected. The most common causes of meningitis are viral and bacterial infections, but can also be cancer, chemical irritation, fungi, and drug allergies. Viral and bacterial meningitis are contagious. They can be transmitted by coughing, sneezing, or close contact.
Viral and bacterial infections are the most common causes of meningitis. There are several other forms of it. Examples include cryptococcal, which is caused by a fungal infection, and carcinomatous, which is cancer-related. These types are rare.
Viral Meningitis: It is the most common type of meningitis. Viruses in the Enterovirus category cause 85 % of cases. Viruses in the Enterovirus category cause about 10 to 15 million infections per year, but only a small percentage of people who get infected will develop meningitis. These are more common during the summer and fall, and they include:
- Coxsackievirus A
- Coxsackievirus B
Other viruses can cause meningitis. These include:
- West Nile virus
- Coltivirus, which causes Colorado tick fever.
Bacterial Meningitis: It is contagious and caused by infection from certain bacteria. It is fatal if left untreated. Between 5 to 40 % of children and 20 to 50 % of adults with this condition die. This is true even with proper treatment. The most common types of bacteria that cause bacterial meningitis are:
- Streptococcus Pneumoniae: It is typically found in the respiratory tract, sinuses, and nasal cavity, and can cause meningitis called “pneumococcal meningitis”.
- Neisseria meningitides: It is spread through saliva and other respiratory fluids and causes meningitis called “meningococcal meningitis”.
- Haemophilus influenza: This can cause not only meningitis but infection of the blood, inflammation of the windpipe, cellulitis, and infectious arthritis.
- Listeria monocytogenes: It is a foodborne bacteria.
|Neonates (<3 month)><3 month)||Children||Adults||Elderly (>65)|
|Group B Streptococcus Escherichia coli Listeria monocytogenes||Streptococcus pneumonia Neisseria meningitides Haemophilus Influenzae type B||Streptococcus pneumonia Neisseria meningitides||Streptococcus pneumonia Neisseria meningitides Listeria monocytogenes|
Table: CSF findings in meningitis by etiologic agent
|Agent||Opening pressure (mm H2O)||WBC count (cells/µL)||Glucose (mg/dL)||Protein (mg/dL)||Microbiology|
|Bacterial meningitis||200-300||100-5000; >80% PMNs||< 40||>100||Specific pathogen demonstrated in 60% of gram stains and 80% of cultures.|
|Viral meningitis||90-200||10-300; lymphocytes||Normal, reduced in LCM and mumps||Normal but maybe slightly elevated||Viral isolation, PCR assays|
|Tuberculous meningitis||180-300||100-500; lymphocytes||Reduced, < 40||Elevated, >100||Acid-fast bacillus stain, culture, PCR|
|Cryptococcal meningitis||180-300||10-200; lymphocytes||Reduced||50-200||India ink, cryptococcal antigen, culture|
|Aseptic meningitis||90-200||10-300; lymphocytes||Normal||Normal but maybe slightly elevated||Negative findings on workup|
|Normal values||80-200||0-5; lymphocytes||50-75||15-40||Negative findings on workup|
LCM = lymphocytic choriomeningitis;
PMN = polymorphonuclear leukocyte;
PCR = polymerase chain reaction;
WBC = white blood cell.
Clinical Features and Pathophysiology:
Chills, Rigors or Fever (T>38°):
- Endogenous cytokines (released during the immune response to the invading pathogens) affect the thermoregulatory neurons of the hypothalamus, changing the central regulation of body temperature.
- Invading viruses or bacteria produce exogenous substances (pyrogens) that can also re-set the hypothalamic thermal set point.
Nuchal rigidity (neck stiffness):
- Flexion of the spine leads to stretching of the meninges.
- In meningitis, traction on the inflamed meninges is painful, resulting in a limited range of motion through the spine (especially in the cervical spine).
Altered mental status: ↑ ICP → brain herniation → damage to the reticular formation (structure in the brainstem that governs consciousness).
Focal neurological deficits:
- Cytotoxic edema and ↑ ICP lead to neuronal damage.
- Signs or symptoms depend on the affected area (cerebrum, cerebellum, brainstem, etc.)
Examples: Cranial nerve palsies, hemiparesis, hypertonia, nystagmus.
Seizures: Inflammation in the brain alters membrane permeability, lowering the seizure threshold. The exact seizure pathophysiology is unknown.
Headache: Bacterial exotoxins, cytokines, and ↑ ICP stimulate nociceptors in the meninges (cerebral tissue itself lacks nerve endings that generate pain sensation).
Photophobia: Due to meningeal irritation. Mechanisms unclear; pathways are thought to involve the trigeminal nerve.
Nausea and vomiting: ↑ ICP stimulates the area Postrema (vomiting center), causing nausea and vomiting.
Petechial rash: Meningococcemia (due to N. meningitidis)
In the pediatric population, all of the above signs and symptoms are applicable. Additional signs and symptoms in children include:
- Bulging fontanelles,
- Bones of the skull do not join fully (form sutures) until age 2,
- ↑ ICP → meninges protrude through gaps in skull bones,
- Impaired bilirubin excretion,
- Exact mechanism unclear, associated with sepsis,
- Reduced feeds, irritability, lethargy, and toxic appearance,
- Fever, shock, and cerebral edema can lead to such manifestations in children.
The longer the cause of the disease without treatment, the greater the risk of seizures and permanent neurological damage. The following complications are typically associated with meningitis:
- Hearing loss
- Gait problems
- Memory difficulty
- Learning disabilities
- Brain damage
- A subdural effusion, or a buildup of fluid between the brain and the skull
- Kidney failure
|Viral meningitis||Bacterial meningitis|
|In infants |
• Decreased appetite
• A fever
• A fever
• Stiff neck
• Sensitivity to bright light
• Decreased appetite
|• Altered mental status |
• A sensitivity to light
• Irritability • A headache
• A fever
• A stiff neck
The following are some of the risk factors for meningitis:
Compromised Immunity: An immune deficiency is more vulnerable to cause meningitis infections. Certain disorders and treatments can weaken the immune system. These include:
- Autoimmune disorders
- Organ or bone marrow transplants
Cryptococcal meningitis, which is caused by a fungus, is the most common form of meningitis in people with HIV or AIDS.
Community Living: It is easily spread when people live in close quarters. Being in small spaces increases the chance of exposure. Examples of these locations include:
- College dormitories
- Boarding schools
- Day care centers
Pregnancy: Pregnant women have an increased risk of listeriosis, which is an infection caused by the Listeria bacteria. Infection can spread to the unborn child.
Age: All ages are at risk for meningitis. Children under the age of 5 are at increased risk of viral meningitis. Infants are at higher risk of bacterial meningitis.
Working with Animals: Farmworkers and others who work with animals have an increased risk of infection with Listeria.
- Physical exam: Physical exams like monitoring of fever, an increased heart rate, neck stiffness, and reduced consciousness can be important clues for the diagnosis of meningitis in the early stage.
- Lumbar puncture: This test is also called a spinal tap. It allows looking for increased pressure in the central nervous system. It can also find inflammation or bacteria in the spinal fluid. This test can also help to determine the best antibiotic for treatment.
- Blood cultures: Identification of bacteria in the blood. Bacteria can travel from the blood to the brain. N. meningitides and S. pneumonia can cause both sepsis and meningitis.
- Complete blood count: A complete blood count with differential is a general index of health. It checks the number of red and white blood cells in the blood. White blood cells fight infection. The count is usually elevated in meningitis.
- Chest X-rays: Chest X-rays can reveal the presence of pneumonia, tuberculosis, or fungal infections. Meningitis can occur after pneumonia.
- CT scan: A CT scan of the head may show problems like a brain abscess or sinusitis. Bacteria can spread from the sinuses to the meninges.
Bacterial or severe viral meningitis may require treatment in a hospital, including:
- Medicines such as antibiotics, corticosteroids, and medicines to reduce fever.
- Oxygen therapy, for patients who have trouble breathing.
- Supportive care. In the hospital, watch the person closely and provide care if needed. For example, if the patient may need to drink extra liquids or get fluids in a vein (IV).
- Maintaining a healthy lifestyle,
- Getting adequate amounts of rest,
- Not smoking,
- Avoiding contact with sick people,
- Vaccinations can also protect against certain types of meningitis. Vaccines that can prevent meningitis include the following:
- Haemophilus Influenzae type B (Hib) vaccine
- Pneumococcal conjugate vaccine
- Meningococcal vaccine
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