Infectious Diseases
Overview
An infection is an illness caused by the invasion of a virus or microorganism. The microorganisms are usually bacteria, but they also include animal parasites and fungi. Infections range from mild to very serious and can affect any part of the body, including the nervous system. When an infection invades the nervous system, it is referred to as a neurological infection. The most common neurological infections are meningitis, an inflammation of the membranes that cover the brain and spinal cord; encephalitis, an inflammation of the brain; and complications caused by the HIV virus which affects the nervous system, along with various other parts of the body.
The classical symptoms of infection (including neurological infections) are pain, swelling, redness, heat (either a fever or heat at the sight of the infection), and sometimes impaired function.
Encephalitis
Encephalitis is an infection in the brain itself. (Meningitis is an infection in the meninges that cover the brain.) Like meningitis, encephalitis can be caused by either bacteria or viruses, including viruses transmitted by mosquitoes or other arthropods (an arthropod is a group of animals including the insects and ticks). It can develop slowly or quickly, and it can be either very mild or quite severe, depending on the organism that is causing the infection.
Types & Causes
Arboviruses
An arbovirus (arthropod-borne virus) is a virus that is transmitted by an arthropod, including insects and ticks. There are many different types of arboviral encephalitis, which exist worldwide, including four in the United States: eastern equine encephalitis (EEE), western equine encephalitis (WEE), St. Louis encephalitis (SLE), and LaCross encephalitis (LAC), all of which are transmitted through mosquitoes. Most cases of arboviral encephalitis occur during the summer, when the mosquitoes are active.
Most people who are infected with an arbovirus show no signs of infection. Or, they may show only mild, flu-like symptoms such as fever and headache. Only a very small percentage of infections develop into full-blown encephalitis. Those that do, however, are quite serious and can cause death or permanent neurological damage.
Herpes Simplex Encephalitis (HSE)
HSE is the most fatal encephalitis. It tends to develop in both very young and very old people, although it can develop at any age. Most people are exposed to the virus at some point in their life, and often the virus lives inside of a person for many years before it begins to cause any problems. It is not clear why it causes encephalitis in some people but not others.
HSE often causes swelling in the brain and significant neurological dysfunction.
Rabies
Rabies is a virus that is transmitted by mammals, especially bats, skunks, foxes and raccoons. If a rabid animal bites a person, the person may develop a rabies infection, including severe encephalitis. The encephalitis symptoms of a rabies infection include agitation, hallucinations, and muscle spasms. If left untreated, a person can develop seizures and coma.
Diagnosis
Medical History
As with all neurological disorders, a complete medical history is the first step in diagnosing encephalitis. It is essential that your physician know where you have traveled recently, any contact you had with unusual animals or ill people, and a history of insect bites.
Neurological Examination
A complete neurological exam should be done to look for any abnormalities that serve as clues about which specific area of the brain is affected.
Imaging Studies
Imaging studies are tests that provide computer images of the inside of the brain and involve either a CT scan (computer axial tomography) or MRI (magnetic resonance imaging). An MRI can often show damage to a particular brain area and may be more useful for diagnosing encephalitis.
Spinal Tap (Lumbar Puncture)
A spinal tap, or lumbar puncture, involves inserting a needle into the lower back (the lumbar area of the spine) and collecting some cerebrospinal fluid. The fluid is then sent to a lab where it is examined under the microscope and the organism causing the infection can be identified. Specialized molecular techniques are used to determine which particular virus is causing the encephalitis pictures.
Treatment
The treatment for encephalitis depends on the cause.
Arboviral Encephalitis
There is no treatment for arboviral encephalitis, and there are no vaccines for the United States. In areas where arboviral encephalitis occurs, public health officials usually initiate insecticide spraying to kill the mosquitoes. In areas where mosquitoes known to be carrying an arbovirus live, people should do what they can to avoid being bitten (e.g., wearing insect repellant, avoiding going outside during times of the day when the mosquitoes are most active, etc.).
Herpes Simplex Encephalitis
This type of encephalitis can be treated with an antiviral drug called Acyclovir, which is given intravenously and is also used to treat genital and skin infections caused by a herpes simplex infection. Without treatment, herpes simplex encephalitis can (and probably will) be fatal, so treatment should be started immediately upon diagnosis.
Rabies Encephalitis
Rabies is a disease that is best treated through prevention. The animal that bit the person should be found. If it is wild, or if there is no proof that it has been vaccinated, it should be given to a pathologist who will kill the animal and examine its brain for the presence of the rabies virus. If the animal cannot be found, or if there is any question whatsoever about whether it is infected or not, the person should be treated immediately with human rabies immunoglobulin, an antibody that acts against the rabies virus.
HIV and the Nervous System
HIV (human immunodeficiency virus) is the virus that causes AIDS-acquired immunodeficiency syndrome. It invades and impairs the body's immune system, that is, all the parts and processes of the body that fight disease and infection. As a result, HIV-infected patients lose their ability to protect the body from various infections, including neurological infections. HIV can live for a long time inside of a person's body before any signs of a suppressed immune system begin to show.
HIV can cause damage to both the central nervous system, the brain and spinal cord, and the peripheral nervous system, all the nerves leading to and from the central nervous system. The damage varies from person to person. It is caused by either the HIV virus itself, AIDS-related cancers, or other infections that an otherwise healthy immune system would be able to prevent.
The most common HIV neurological infection is cerebral toxoplasmosis, a protazoa (type of parasite) that causes tissue damage leading to speech difficulties, seizures, confusion and lethargy. HIV infection can lead to encephalitis, a swelling of the brain, or meningitis, a swelling of the membranes that surround the brain. It can cause problems with thinking (AIDS dementia complex), and it can cause changes in behavior.
Progressive multifocal leukoencephalopathy (PML) is another HIV-related disorder associated with several neurological problems such facial weakness, loss of vision, and memory loss. HIV can also lead to neuropathy (a nerve disorder) and myopathy (a muscle disorder).
Signs and Symptoms
Central Nervous System
If the central nervous system is affected, patients may develop weakness, seizures, a change in their mental status, headaches, and language problems. If they have PML in particular, they may suffer from dementia (a broad range of cognitive problems, including memory loss, poor judgment, etc.), facial weakness, visual problems, and a loss of coordination. Generally, the symptoms reflect what particular part of the brain is affected. The most common central nervous system disorder in HIV patients is the infection toxoplasmosis, followed by HIV-related brain cancer.
Peripheral Nervous System
If the HIV infection affects the peripheral nervous system, then the nerves and muscles show various signs of dysfunction. Patients with a peripheral neuropathy (disease in the nerves that lead from the spinal cord to all the various parts of the body) may feel strange burning and tingling sensations, may experience numbness, or their arms and legs may ache. If the motor neurons in particular are involved (the nerves that lead to the skeletal muscles), a patient's muscles may weaken. Patients may develop breathing or heart problems.
Types & Causes of Central Nervous System Disorders
Cerebral Toxoplasmosis
Cerebral toxoplasmosis, also known simply as toxoplasmosis, is the most common central nervous system infection in HIV patients. It is caused by a protozoa, Toxoplasma gondii, which lives in the soil and in animal feces. Most people in the United States are exposed to it at some point in their life but don't suffer any of the signs of infection. In HIV patients and other people with suppressed immune systems, however, the bacteria can cause brain abscesses (tissue damage and the accumulation of pus), the symptoms of which vary depending on where in the brain the infection is located. The usual symptoms of toxoplasmosis include speech difficulties, seizures, confusion and lethargy. Symptoms usually develop over the course of days to weeks.
Cryptococcal Meningitis
Cryptococcal meningitis is a type of meningitis that is caused by a fungus. The course of the illness is usually slow and may develop over days or months. See meningitis for details of symptoms, diagnosis and treatment.
Progressive Multifocal Leukencephaly (PML)
PML is an infection caused by a rare virus. A patient with PML may suffer from dementia (a broad range of cognitive problems, including memory loss, poor judgement, etc.), facial weakness, visual problems, and a loss of coordination. The symptoms vary from person to person and generally reflect what particular part of the brain is affected.
HIV-Related Cancer
Central nervous system lymphoma is the second most common nervous system abnormality in HIV patients after toxoplasmosis. Primary lymphoma generally develops in the central nervous system only in people, like HIV patients, who have suppressed immune systems. Primary lymphoma, as opposed to metastatic lymphoma, is cancer that actually originates in the lymphatic system and has not spread from some other part of the body.
Peripheral Nervous System Disorders
Neuropathy
Neuropathy, also known as peripheral neuropathy, is disease in the peripheral nerves-the nerves that lead to and from the spinal cord and connect with all the various parts of the body. It is very common in HIV patients, usually in the later stages of HIV disease. It can manifest itself in several different ways.
Distal symmetric neuropathy. The most common form of HIV-related neuropathy affects the feet first and then the hands, and it affects both sides of the body equally. Patients often feel a strange tingling and painful burning sensation that can spread up the legs and arms. Some patients feel numbness or weakening in the arms and legs.
Acute Inflammatory Demyelinating Neuropathy
This is very similar to Guillain-Barre syndrome. It involves the nerve root (where the root connects with the spinal cord) and the myelin sheath that surrounds and protects the nerves. The onset of this kind of neuropathy is usually very rapid, sometimes developing within hours to days.
Myopathy: Polymyositis
Myopathies are neurological disorders that involve the skeletal muscles-muscles that are connected to bones, like the biceps in the upper arm and quadriceps in the thigh.
There are many different types of myopathies (including, for example, the muscular dystrophies), but the most common type that affects HIV patients is polymyositis, or PM. Most people with PM don't feel the intense muscular pain that other myopathies cause, but they do suffer muscular aches, cramping and tenderness. The muscle weakness, on the other hand, is quite intense. It is often worse in the neck, arms and upper portion of the legs, making it difficult to stand up from a sitting position. Many patients also experience fever, malaise (general bodily discomfort) and loss of appetite.
Diagnosis of HIV-Related Neurological Disorders
Central Nervous System Disorders
Usually, diagnoses of central nervous disorders are based on CT scan or MRI imaging studies, tests that provide computer pictures of the inside of the brain. Often, a dye is injected into the body that provides better tissue contrast, making it easier to detect abnormalities and lesions in the brain.
If an infection is suspected, a spinal tap, also known as a lumbar puncture, is done, which involves collecting cerebrospinal fluid so that it can be examined microscopically for the presence of bacteria or viruses. A spinal tap also provides information about the white blood cells, and glucose and protein concentrations, all of which can provide clues about what is causing the problems.
Sometimes, if the various other tests do not provide a clear diagnosis, a brain biopsy may be performed. This involves surgically removing a small sample of brain tissue which is then sent to a lab for microscopic evaluation. A biopsy is sometimes necessary to confirm a cancer diagnosis, for example.
Peripheral Nervous System Disorders
A complete neurological exam should be done to look for any noticeable abnormalities, such as irregular muscle and eye movements, that reflect a neurological disorder.
Usually, neurophysiological tests are done to look for abnormal nerve and muscular activity. These include the electromyography (EMG) and nerve conduction velocity study (NCV). An EMG involves placing very tiny electrode needles into the muscles, and if there are any abnormalities evident, it is likely that the nerve supplying the muscle is somehow damaged. The NCV involves placing electrodes on different places on the skin where particular nerves are known to be located. Very small electrical shocks are given, and using an oscilloscope (a TV screen monitor), the nerve function can be monitored and the speed at which an impulse travels along the nerve can be determined. One of the functions of the myelin sheath is to speed up transmission of the nervous system signals, so if the speed is slower than normal it suggests that the myelin sheath may be damaged, which indicates that the disorder may be acute inflammatory demyelinating neuropathy.
Nerve and muscle biopsies are sometimes done if the various other tests do not provide a clear diagnosis.
Treatment
Central Nervous System Disorders
Some neurological problems can be treated with medication or antibiotics. Antidementia drugs can be prescribed to relieve confusion and slow the progression of mental decline. Neurological infections can be treated with antibiotics. There is no known treatment for PML at this time. If there is an AIDS-related tumor in the brain or spinal cord, radiation therapy or steroid use may be helpful, although the prognosis is poor.
Peripheral Nervous System Disorders
Treatment of the various peripheral nervous system disorders usually focuses on relieving the pain and other symptoms. Drug therapy is often used to treat neuropathic pain. Typical medications include the tricyclic antidepressants such as amitriptyline (Elavil), anticonvulsants such as gabapentin (Neurontin), and analgesics such as tramadol (Ultram).
Acute inflammatory demyelinating syndrome is caused by abnormal immune system proteins attacking the myelin sheath, just as in Guillain-Barre syndrome. It often requires immunotherapy or plasmaphoresis as part of its treatment. Immunotherapy involves injecting a specific protein into the blood that plays an important role in protecting the body from infection. The protein stops the abnormal immune response that is causing the neuropathy. Plasmaphoresis involves removing some of the blood, separating the cells from the plasma, and then reinjecting the cells back into the body.
Meningitis
Meningitis (or spinal meningitis as it commonly known) is an infection in the meninges and cerebrospinal fluid. The meninges are three thin layers of membrane that cover the brain and spinal cord. The cerebrospinal fluid is watery layer of cushion just beneath the meninges that bathes and protects the brain and spinal cord from physical impact.
Meningitis is usually caused by either a bacteria or virus. Viral meningitis is generally mild and self-limiting, meaning that it disappears on its own without any treatment. Bacterial meningitis, on the other hand, can be quite severe and can lead to permanent hearing loss, learning disability, or other types of brain damage.
There are several different bacterial strains that can cause meningitis, some of which can be readily treated with antibiotics. HIV (human immunodeficiency virus) can cause meningitis at some point during the course of a person' s illness, but the meningitis is actually caused by a fungus and not HIV itself.
Most people who are infected with a bacteria or virus that could potentially cause meningitis never actually get sick. For example, according to the Meningitis Research Foundation, for every 1000 people who are infected with a meningitis virus, only one person will actually become ill. The same is true of bacterial meningitis. It is not clear these few people actually develop meningitis from microorganisms and viruses that are apparently harmless to the rest of us. It is likely due to a weakness in the immune system.
Types & Causes
Viral Meningitis
Viral meningitis, also known as aseptic meningitis, is the most common type of meningitis and is caused by an infection of one of several different types of viruses. Viral meningitis is serious but rarely fatal.
The symptoms usually last no more than about 10 days, and then the person recovers fully without any treatment. The viruses that cause viral meningitis are contagious and are very common in the summer and early fall, but most people who have one of the viruses show no symptoms of any kind.
Sometimes a person may develop a cold or a rash, but full-blown meningitis develops in fewer than 1 in 1000 people who are infected with a meningitis virus. Consequently, if you are around somebody who has viral meningitis, you have a very small chance of developing it yourself, even if you get infected. About 90% of all viral meningitis cases involve a type of virus known as an enterovirus. The mumps and herpes virus can also cause meningitis.
Bacterial Meningitis
There are several different types of bacteria that can cause bacterial meningitis. It is important to identify the bacteria so that an appropriate antibiotic can be prescribed. Bacterial meningitis can progress quickly and can lead to death, so it is essential that it be diagnosed and treated as soon as possible.
Some forms of bacterial meningitis are contagious and are spread through secretions from the mouth or nose, although they are not nearly as contagious as the common cold or flu. They are not spread by casual contact. However, people living in crowded households or chronic care facilities are at greater risk for developing bacterial meningitis.
There are vaccines for some types of bacterial meningitis. Infants in the United States are routinely vaccinated for the Hib strain, which used to be the most common cause of bacterial meningitis in the country. Outbreaks of meningitis epidemics do occur throughout the world, though not in the United States.
Cryptococcal Meningitis
Cryptoccal meningitis is a type of meningitis that develops in HIV patients and is caused by a fungus. The course of the illness is often a slow one, with symptoms that may progress over days to weeks to even months.
Symptoms
No matter what causes meningitis, the symptoms are the same. The most common symptoms include headache, a stiff neck, and fever. In infants, these symptoms may be difficult to detect. Other symptoms include vomiting, nausea, photophobia (looking into a light is disturbing), confusion, sleepiness, and seizures. Some people may develop a skin rash or joint pains. Some may have an upper respiratory infection or other illness before the symptoms of meningitis start to show.
The symptoms may develop over the course of a few hours or a few days. They usually develop much more quickly in bacterial meningitis and, if untreated, can lead to unconsciousness.
Diagnosis
A clinical & neurological examination can be used to diagnose meningitis. One of the most telling clinical symptoms of meningitis is a stiff neck. It is extremely painful for a person with meningitis to move their neck forward. The neck may be so stiff that if they try to move it, their whole body moves instead. Other clinical signs include a skin rash and a swelling of the nerves in the eye, which indicates an increased pressure in the brain.
Imaging Studies (e.g., CT scan) may be done to view the brain and rule out other possible neurological disorders.
Both viral and bacterial meningitis are usually positively diagnosed by doing a spinal tap, or lumbar puncture, which involves inserting a needle into the lower back (the lumbar area of the spine) and collecting some cerebrospinal fluid. The fluid is then sent to a lab where it is examined under the microscope and whatever is causing the infection can be identified.
Treatment
Most forms of viral meningitis are self-limiting, that is they disappear their own without any treatment. Bacterial meningitis, on the other hand, and should be treated with antibiotics as soon as possible. If bacterial meningitis is suspected, antibiotics should be administered even before the spinal fluid is collected to confirm the diagnosis. Bacterial meningitis should be considered a potentially life-threatening emergency. Patients may also experience secondary symptoms, like changes in their blood pressure, that need to be treated as well.