What is Meningitis?
Meningitis occurs when inflammation from some type of infection affects the meninges, the tissue covering the brain and spinal cord. These infections may be bacterial, viral or fungal in origin. Rarely, meningitis may also occur in reaction to some medications or diseases (e.g., cancer). Anyone can develop meningitis, although it tends to occur most frequently in older adults, young children and individuals with a long-standing health condition (e.g., HIV/AIDS). However, cases of bacterial meningitis among adolescents and young adults may be becoming more common in the United States and United Kingdom.
The central nervous system includes the brain and spinal cord. Its neural tissues are protected by three membranous layers of connective tissue called meninges. The meninges also enable the vertebral column and spinal cord to flex and twist.
The outermost layer of the meninges is called the dura mater. It fuses with the lining of the skull. The middle layer of the meninges is called the arachnoid mater. This membrane is separated from the delicate, innermost membrane (pia mater) by a space that contains cerebrospinal fluid (CSF). This fluid carries nutrients, helps absorb impact and helps defend the brain from harmful microorganisms.
Bacteria, viruses or fungi reach the meninges through the bloodstream, from nearby infections (e.g., sinusitis) or by direct contact (e.g., penetrating injury, surgical procedure). While in the bloodstream, these microorganisms resist attack by white blood cells, causing receptors in the brain to allow penetration into the CSF. Once in the CSF, infection tends to progress rapidly due to the lack of disease-fighting substances (antibodies). The resulting inflammation causes oozing fluid called exudate to damage cranial nerves and pathways that carry signals to other parts of the body. It also causes swelling of the meninges, which disrupts the normal flow of blood and oxygen to the brain.
Types and differences of meningitis
Meningitis can be classified into three types:
Viral (aseptic) meningitisThe most common form of meningitis, it tends to be relatively mild. Each year, between 25,000 and 50,000 cases of viral meningitis require hospitalization, according to the U.S. Centers for Disease Control and Prevention (CDC). Most patients with viral meningitis have symptoms that go away without any special treatment. However, symptoms of viral meningitis may closely resemble those associated with bacterial meningitis, a much more serious form of the disease that requires immediate treatment. This similarity may complicate the process of diagnosing the source and severity of the infection. Viral meningitis may be caused by enteroviruses (viruses that infect the intestinal tract) or other viral conditions (e.g., herpes simplex virus, human immunodeficiency virus).
Bacterial meningitisUsually the most severe type of meningitis. Many different types of bacteria can cause bacterial meningitis if they travel through the bloodstream and enter the brain. The most common forms of bacterial meningitis include the bacteria that cause pneumonia (pneumococcus) and meningococcus bacteria (Neissaria meningitides).
According to the CDC, about 6,000 people develop pneumococcal meningitis and 2,600 people develop meningococcal meningitis in the United States each year. Vaccines are available that can prevent some types of bacterial meningitis from spreading to other people. The disease can also occur if bacteria invade the meninges directly (e.g., ear or sinus infections, skull fractures). Left untreated, bacterial meningitis may cause brain damage, deafness, cognitive impairment and even death.
Chronic meningitisInflammation of the meninges that is ongoing or recurrent. Patients with chronic meningitis may experience spontaneous episodes of severe headache and fever, often interrupted by extended periods without painful symptoms. Most cases of chronic meningitis have no known underlying cause, though it occurs relatively frequently in people with compromised immune systems (e.g., due to HIV/AIDS, cancer, chemotherapy use, long-term use of the corticosteroid prednisone). It also sometimes occurs in people with healthy immune systems who contract tuberculosis (TB), Lyme disease or other infections. Bacterial meningitis that has been only partially treated (but not eliminated from the body) may lead to chronic meningitis. Drugs such chemotherapy medications, organ-transplantation medications and nonsteroidal anti-inflammatory drugs have also been associated with chronic meningitis.
Meningitis signs and symptoms
Symptoms of meningitis vary depending on the nature of the infection. In the case of viral meningitis, symptoms may be very mild and resemble those of a cold, sometimes accompanied by low-grade fever and a rash. In some cases, no symptoms appear at all.
However, all cases of meningitis require emergency medical attention because some forms of meningitis are potentially serious and even fatal. Any symptoms that appear should be treated seriously.
Symptoms of meningitis infection may appear in as little as 24 hours, and in severe cases they may rapidly progress. Such symptoms may include:
- Confusion or disorientation
- Stiff or painful neck (resulting in difficulty or inability to touch chin to chest)
- Muscle aches or weakness
- Sensitivity to light
- Skin rash
How is it diagnosed?
To diagnose meningitis, a physician will review a medical history and perform a physical examination. One method of diagnosing meningitis is to bend the neck of a patient forward while the person lies flat on his or her back. A person with meningitis will involuntarily flex the knees in response. This is believed to be a reaction to irritation of the inflamed meninges.
Certain medical tests may also be performed that can help determine the nature of the meningitis (e.g., viral or bacterial). If the meningitis is bacterial, these tests can help identify the specific type of bacterium responsible, which can help the physician to devise a more effective treatment plan. It may take a few days before the results of these tests are available.
These tests include:
- Spinal tap. The insertion of a long needle into the spinal canal to collect cerebrospinal fluid (CSF) for laboratory testing. Analysis of CSF is the only definitive diagnosis method of meningitis. CSF is checked for indicators of an infection (e.g., the number of white blood cells, glucose and protein levels) and then interpreted by a physician to determine if meningitis is present. CSF may also help identify if the source of infection is bacterial or viral. A spinal tap is nearly always performed if meningitis infection is suspected.
- Throat culture. The back of the throat is swabbed and examined under a microscope. A throat culture can determine if the presence of microorganisms that can cause meningitis or a disease with similar symptoms (e.g., encephalitis) are present. In addition, it may also be helpful in determining the appropriate course of treatment.
- Imaging tests. Tests that produce images of internal body organs, tissues, structures and pathways (e.g., x-ray, CAT scan, MRI). Imaging tests of certain parts of the body (e.g., chest, skull) may show swelling or inflammation consistent with meningitis and the severity of the infection.
- Urine tests. Urine may be tested to check for the cause of painful symptoms associated with meningitis.
- Blood tests. Blood may be analyzed to check counts of white and red blood cells and biochemistry (hormone levels). Cultures of blood can be developed that can be examined for the presence of bacteria or viruses.
- Polymerase chain reaction (PCR). A DNA test that checks blood for the presence of viruses or parasites. A PCR may be performed if a patient is suspected of having meningitis.
- Biopsy. Rarely, a sample of tissue from a rash thought to be caused by meningitis may be removed for laboratory analysis.
How is Meningitis treated?
If the diagnosis is acute bacterial meningitis, antibiotic drug therapy is started immediately. Choice of antibiotics depends on the type of bacteria causing the infection. In some cases, treatment for brain swelling, shock, convulsions, or dehydration may also be needed. Treatment of aseptic meningitis is directed at pain relief (analgesics) and fever reduction. Treatment of subacute meningitis varies depending on the cause of the disease (fungus, tuberculosis, syphilis). In recurrent meningitis, drainage of infected sinuses or mastoids may be necessary.
Noroxin (Norfloxacin), Myambutol (Ethambutol)
Prognosis depends on the causative organism and the severity of the illness. In most cases, recovery is possible with prompt and appropriate treatment. However, in some cases, brain damage may occur. Underlying conditions such as being on immunosuppressant medications, cancer (malignancy), HIV infection, and alcoholism worsen the prognosis.
Differential diagnoses include subarachnoid hemorrhage, bacterial endocarditis, malignant hypertension, lead poisoning, porphyria, migraine, viral encephalitis, cerebral abscesses, cerebral tumor, and subdural hematoma.
Neurologist and infectious disease specialist.
Last updated 11 July 2015