Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 89. Infections of the Brain and Spinal Cord

Topics: Introduction | Acute Bacterial Meningitis | Chronic Meningitis | Viral Infections | Brain Abscess | Subdural Empyema | Parasitic Infections

Acute Bacterial Meningitis

Acute bacterial meningitis is rapidly developing inflammation of the meninges caused by bacteria.

Acute bacterial meningitis is most common among children aged 1 month to 2 years (see Section 23, Chapter 272). It is much less common among adults. However, small epidemics of meningitis may occur among self-contained groups of people, such as those in military barracks or in college dormitories.

Causes

Two species of bacteria account for most cases of acute bacterial meningitis: Neisseria meningitidis and Streptococcus pneumoniae. Both are normally present in the external environment and may even reside in a person's nose and upper respiratory system without causing harm. Occasionally, these organisms infect the brain without an identifiable reason. In other cases, infection develops because the immune system is impaired--as it is in people who have an HIV (human immunodeficiency virus) infection. Or, infection may result from a head injury. For example, a skull fracture may create an opening between the nasal sinuses and the space around the meninges (which contains cerebrospinal fluid). Bacteria can travel from the sinuses through the opening and infect the meninges. People most at risk of developing meningitis due to Neisseria meningitidis and Streptococcus pneumoniae are those who abuse alcohol; those who have had a splenectomy (removal of the spleen); those who have chronic infections of the middle ear, nose, or sinuses; and those who have pneumococcal pneumonia or sickle cell disease.

Listeria monocytogenes causes about 10% of cases of bacterial meningitis. People who have kidney failure or who are taking corticosteroids (which suppress the immune system) have a higher-than-average risk of developing meningitis due to Listeria bacteria.

Other types of bacteria can also cause meningitis. Meningitis due to Escherichia coli (found normally in the colon and in feces) or Klebsiella bacteria usually develops after a head injury, brain or spinal cord surgery, a widespread infection of the blood (sepsis), or an infection acquired in a hospital. These infections are more common among people with an impaired immune system. Newborns, whose immune system is not completely formed, are at increased risk of developing infections due to Escherichia coli or group B streptococci.

Symptoms

Early symptoms of acute bacterial meningitis are a fever, headache, stiff neck, sore throat, and vomiting. These symptoms are sometimes preceded by a cough and other symptoms suggesting a respiratory illness. The stiff neck is more than just soreness: Trying to lower the chin to the chest causes pain and may be impossible. A skin rash (usually red and purple spots) may develop because of inflammation and bleeding in small blood vessels throughout the body, including those under the skin.

In children up to 2 years old, acute bacterial meningitis usually causes a fever, feeding problems, vomiting, irritability, seizures, and high-pitched crying. The skin over the fontanelles (soft spots between the skull bones) becomes taut, and the fontanelles may bulge. The flow of cerebrospinal fluid around the brain may become blocked, causing the fluid to accumulate and the skull to enlarge (a condition called hydrocephalus). Unlike older children or adults, infants younger than 1 year may not develop a stiff neck (see Section 23, Chapter 272).

Adults may become desperately ill within 24 hours, and children even sooner. Older children and adults can become irritable, confused, then increasingly drowsy. Drowsiness can progress to stupor, coma, and death. The infection causes swelling of brain tissue, increasing pressure inside the skull, and hampers blood flow, causing stroke symptoms and paralysis. Some people have seizures.

Bacterial meningitis can spread from the meninges to the brain. In such cases, the disorder is technically called meningoencephalitis, but most doctors still refer to it as meningitis.

Infection with Neisseria meningitidis affects many organs. When it becomes very severe, it produces severe diarrhea, vomiting, internal bleeding, low blood pressure, shock, and death. These effects can develop rapidly and are called the Waterhouse-Friderichsen syndrome.

Diagnosis

If a child 2 years old or younger has an unexplained fever and the parent senses that the child is ill, the parent should call a doctor immediately. A child who becomes increasingly irritable or unusually sleepy, refuses to eat, vomits, has seizures, or develops a stiff neck requires immediate medical evaluation. In adults, fever, headache, skin rash, confusion, unresponsiveness (stupor), seizures, and a stiff neck also require immediate evaluation.

During the physical examination, doctors look for telltale signs of meningitis, such as a stiff neck and the characteristic skin rash. One way doctors test for meningitis is to bend the person's neck forward while the person is lying on the back. This maneuver causes a person with meningitis to involuntarily flex the knees. Doctors may then try to straighten the person's flexed knees; such straightening is difficult if the person has meningitis. The person with meningitis is thought to respond in these ways because the maneuvers stretch and therefore further irritate the inflamed meninges.

When doctors suspect meningitis, they must quickly decide whether to treat it immediately or to first perform procedures to determine the specific cause. If the person appears ill, one or more antibiotics are given immediately, before results of diagnostic procedures are known. If the person does not appear ill, treatment may be delayed until procedures are performed to determine whether meningitis is due to bacteria, a virus, another organism, or a noninfectious condition (such as an autoimmune reaction or use of certain drugs).

Usually, a spinal tap (lumbar puncture (see Section 6, Chapter 77)) is performed to diagnose meningitis and determine its cause. A thin needle is inserted between two vertebrae in the lower spine to withdraw a sample of cerebrospinal fluid. Sugar and protein levels and the number and type of white blood cells in the fluid are determined; this information helps doctors distinguish between bacterial and viral infections. Doctors examine the fluid under a microscope to check for and identify bacteria. If they do not see any bacteria, doctors perform other tests that can rapidly identify certain bacteria, such as Neisseria meningitidis and Streptococcus pneumoniae. These tests include analysis of the cerebrospinal fluid for evidence of antibodies against the bacteria and polymerase chain reaction (PCR) techniques, which cause DNA to make copies of itself.

A sample of the cerebrospinal fluid is sent to a laboratory, where the bacteria can be grown (cultured) and identified. The bacteria can be tested for susceptibility to treatment with different antibiotics, so that the antibiotic therapy that was started immediately can be adjusted if necessary.

Doctors may also consider a different cause of the symptoms, such as infection by a virus or fungus. The cerebrospinal fluid may be analyzed further to identify viruses, such as herpes simplex, and other organisms that routine procedures do not identify.

Doctors may also culture samples of blood, urine, mucus from the nose and throat, and pus from skin infections to help make the diagnosis.

Treatment and Prognosis

Because acute bacterial meningitis, especially when caused by Neisseria meningitidis, can lead to death within hours or days, treatment is usually started immediately, without waiting for the results of diagnostic procedures. One or more antibiotics (see Section 17, Chapter 192) are given intravenously. For people who are very ill, antibiotics are started even before a spinal tap is performed. Doctors base their choice of initial antibiotic therapy on the information available, including that from a quick examination of the cerebrospinal fluid. They choose antibiotics that are effective against the bacteria most likely to be causing the infection. Once the species of bacteria is identified (1 or 2 days later), the antibiotics may need to be changed to ones that are most effective against the species identified.

In children, corticosteroids, such as dexamethasone, are also given. After treatment with antibiotics, inflammation develops because the antibiotics break bacteria into fragments. Corticosteroids can suppress the inflammation and reduce the resulting swelling in the brain and increased pressure within the skull. Their use is beneficial in children, but their benefit is less clear in adults. Corticosteroids are not usually given to people who have a serious infection (because these drugs suppress the immune system), but bacterial meningitis is an exception. A corticosteroid is best started before or with the first dose of antibiotics and continued for only one or two days. Corticosteroids are especially dangerous when the cause of meningitis and thus the adequacy of antibiotic therapy are uncertain.

Treatment also includes replacing fluids lost because of fever, sweating, vomiting, and poor appetite.

Complications of acute bacterial meningitis may require specific treatment. If seizures occur, anticonvulsants are given (see Section 6, Chapter 85). If shock (see Section 3, Chapter 24) develops (as can occur in the Waterhouse-Friderichsen syndrome), additional fluids and certain drugs (given intravenously) may be given to increase blood pressure.

If pressure within the skull is dangerously increased, the person is put on a ventilator to increase the breathing rate. Increasing the breathing rate reduces the carbon dioxide level in the blood, which controls the volume of blood in blood vessels within the skull. Thus, blood volume and pressure within the skull decrease. Mannitol may be given intravenously. It causes water in the brain to move into the bloodstream and thus reduces pressure within the skull. Corticosteroids are useful because they help the inflamed blood vessels repair themselves. The blood vessels can then actively move excess water in the brain into the bloodstream. Pressure within the skull may be monitored with a small tube (catheter) inserted through a tiny opening drilled through the skull. The tube is connected to a gauge, which registers the pressure.

If treated immediately, most people who have acute bacterial meningitis recover fully. But when diagnosis or treatment is delayed, permanent brain damage or death becomes more likely, especially in very young children and older people. Some people develop seizures that require lifelong treatment. Neurologic problems, such as permanent mental impairment and paralysis, may also result.

Prevention

A vaccine can help prevent meningitis caused by Neisseria meningitidis. The vaccine is used mainly when an epidemic occurs, when there is a threat of an epidemic in a self-contained group of people (such as those in military barracks), or when people may be repeatedly exposed to the bacteria. Family members, medical personnel, and others in close contact with people who have meningitis due to Neisseria meningitidis should be given an antibiotic (such as rifampin or minocycline) as a preventive measure. Children are now routinely immunized with Haemophilus influenzae type b vaccine, which has eliminated what once was the most common cause of meningitis in children.