Overview of Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy
Demyelinating neuropathies are conditions where the protective coating of nerve cells is damaged. These can be due to inherited disorders, exposure to toxic substances, or caused by the body’s immune system. Among these neuropathies, we have one that is caused by the body’s immune response called Guillain-Barre syndrome (GBS), which actually has different forms. In North America, the most common form is called acute inflammatory demyelinating polyneuropathy (AIDP).
This neuropathy happens when the body’s immune system mistakenly targets the nerves, as if they were harmful bacteria or viruses. This is believed to happen because certain microbes, like Campylobacter jejuni, HIV, Epstein-Barr (the virus that causes mononucleosis), and Zika virus, are similar to nerve structures, which confuses the immune system. This results in an inflammatory response, impacting nerve function. There was once a suspicion that vaccines could cause AIDP, but this has been disproven by scientific research.
The symptoms of AIDP usually include a sudden, weak and limp feeling that often starts in the legs and moves upward over time. During a medical examination, the doctor might find weakness in the facial muscles and certain cranial nerves, reduced reflexes, preserved muscle mass, altered sensations, pain, and loss of light and vibration sensations in the affected limbs. In this condition, the motor symptoms are typically more prominent than the sensory ones. In some cases, changes to regular body functions like blood pressure, heartbeat, and even breathing can occur, and in severe cases, the patient might need help with breathing.
AIDP follows a single course, which means it only happens once in a person’s life, but with various degrees of onset, progression, and recovery. Imaging tests may reveal changes in nerves, especially at the lower back.
To confirm AIDP, doctors may need to perform a lumbar puncture, often finding an abnormal level of protein in the fluid surrounding the spinal cord and brain without any signs of infection. In some patients, though, this may not become apparent until about 3 weeks into the condition. For others, this test may come back normal. So, the diagnosis of AIDP requires a detailed patient history, physical examination, investigation of risk factors, imaging of the lumbar spine, thorough studies of the cerebrospinal fluid (the fluid around the brain and spinal cord), and additional tests like electrodiagnostic studies.
These electrodiagnostic tests can help determine the extent of the disease and its cause, and they can provide information about nerve conduction, muscle-nerve connections, and the structural integrity of the nerve fibers. In severe cases, AIDP can affect the axons (the long extensions of nerve cells), which may lead to a worse prognosis. This brief summary mostly focuses on what is typically seen in acute demyelinating polyneuropathies.
Anatomy and Physiology of Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy
Neurons, or nerve cells, are responsible for processing and transmitting information from one cell to another. Essentially, they receive and fire off electrical signals as responses to various stimuli. Neurons have different components: dendrites, bodies, and axons. Dendrites collect information from other nerve cells and are key in the brain’s ability to adapt and change. In the neuron, we find structures that produce proteins and chemicals vital for the transfer of signals at the junction of two nerve cells, known as the synapse.
Axons essentially act as the wire that transmits information to other neurons, glands, and muscles. The ends of axon fibers connect with other cells at the synapse, triggering reactions through certain biological molecules that act on specific cell sites, these can vary depending on the target organ.
Now, let’s talk a bit about how nerve cells conduct signals. At rest, they maintain a resting electrical charge, kind of like a car’s battery when it’s idle. This state is kept through specific channels in the cells which control the concentration of sodium (Na+) and potassium (K+) ions within them. When a nerve cell gets excited or ‘depolarizes’, more sodium ions flood in through special channels in the cell. This causes a positive electric charge inside the cell, stimulating it to send a signal. To reset the charge, potassium channels open to allow potassium ions to exit the cell, causing a temporary over-correction that we call ‘hyperpolarization’. To bring the cell back to its resting state, a little pump in the neurons uses energy to expel 3 sodium ions out of the cell and take in 2 potassium ions. This whole process results in the movement of an electric signal through the nerve cell.
Speed of transmission differs between nerve fibers. Unmyelinated fibers (those not covered by a fatty substance) transmit at speeds from 1 to 5 meters per second. On the other hand, myelinated fibers (those coated with a fatty substance called myelin produced by Schwann cells) can transmit at speeds up to 150 meters per second. This is thanks to a mechanism known as saltatory conduction, where the signal hops from gap to gap in the myelin sheath, kind of like skipping stones across water.
A condition known as AIDP affects the myelinated nerve fibers leading to slowed transmission. In some cases, the nerve fibers themselves can be affected, which can decrease the strength of the nerve signals and lead to abnormal connections between nerves and muscles.
Why do People Need Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy
Electrodiagnostic tests can be crucial for diagnosing and understanding the future course of the disease known as Acute Inflammatory Demyelinating Polyradiculoneuropathy (AIDP). These tests can help doctors understand what’s happening in your nerves and muscles.
Nerve conduction studies are one example of these tests. They examine how well the large nerves in your body, which control your ability to feel and move, are working. However, smaller nerves that control things like pain and sweat need special examinations. The results of these studies can be affected by the room temperature, so it’s important that the room is at an ideal temperature. This test measures several things, including the speed at which nerves are sending signals, the number of healthy muscles that can be activated, and how quickly and synchronously these signals are being transmitted.
The electromyogram, or EMG, is another test that measures how well your nerves and muscles are working together when a small electrical charge stimulates them. This test mainly looks at the responses of a certain type of muscle fiber and may not detect any changes in another type. EMG looks at several features of your body’s electrical activity. This includes things like how vigorous the response is when an electrode is inserted into the muscle, whether the muscle produces abnormal electrical waves, and the nature of the muscle’s activity when you’re trying to use it.
For diagnosing AIDP, these tests are generally performed around three weeks after the symptoms start, to avoid any misleading results. They can also help to rule out other possible conditions that might be causing similar symptoms, such as diseases of the muscles or motor neurons, issues with the connections between nerves and muscles, diseases of the spinal cord or nerve cell bodies, or diseases related to nerve cell bodies, the nerve fiber, or the covering of the nerve fiber.
When a Person Should Avoid Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy
If your doctor thinks you might have Acute Inflammatory Demyelinating Polyneuropathy (AIDP), they might want to do a type of test called electrodiagnostic studies. However, some people should not have these tests.
If you have severe bleeding disorders – which make it harder for your body to control bleeding – you should not have a part of the test called a needle EMG. This test uses needles, which can be dangerous for someone with a bleeding issue.
Also, you should not have the needle EMG test if you have an active infection in the soft tissues, which are the tissues that connect, support, or surround other structures and organs of the body, like muscles, tendons, and fat.
There are also rules for a part of the test called nerve conduction studies. If you have a device in your body to control your heartbeat, an external defibrillator, you should not have nerve conduction studies because they use electricity and could interfere with these devices.
Likewise, if you have a pacemaker, another type of heart device, your doctor needs to know. They should not use electrical stimulation directly on or near the pacemaker. This means, they need to be careful about where they put the electricity for the test.
Equipment used for Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy
To carry out diagnostic tests for a condition called Acute Inflammatory Demyelinating Polyneuropathy (AIDP), your doctor will need certain tools and materials. AIDP is a disorder that involves your immune system attacking your body’s own nerves. The tests for this condition include Electromyography (EMG) and Nerve Conduction Studies (NCS).
The EMG is a test that measures the electrical activity of your muscles, and NCS checks how well your nerves are sending signals. To do these tests, your doctor will use a computer equipment along with special software for these tests.
Additionally, they will use a conduction gel which helps the electrical signals travel better, making it easier for your doctor to get accurate readings. A measuring tape will be used to precisely place the electrodes which are used to pick up the electrical signals from your nerves and muscles.
These electrodes come in different forms. There are surface electrodes that stick to your skin, needle electrodes that are gently inserted into your muscle, and ring electrodes that can slide onto fingers or toes.
Finally, alcohol pads are used to clean your skin before placing the electrodes. This is done to prevent any infections.
Who is needed to perform Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy?
Having well-trained personnel specialising in brain and nerve studies is very important for a proper check-up. These professionals need to know how to use certain equipment known as EMG (Electromyogram – a test that checks the health of the muscles and the nerves controlling the muscles) and NCS (Nerve Conduction Studies – a type of test that measures the speed of conduction of an electrical impulse through a nerve) and understand the information these tests provide.
For these tests to give the best information, it’s important to have a team working together. This team includes technicians who operate the equipment, nurses who take care of the patient’s overall needs, and doctors who are directly involved in patient care. This team works together to make sure the tests are done correctly and the information gathered is correct and detailed.
Preparing for Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy
Just like all nerve tests, it’s important that the temperature is just right, ideally between 32 and 33 degrees Celsius (or around 89.6 to 91.4 Fahrenheit). This is to make sure the test results are accurate. A warming lamp can be used to make sure the limb being tested is at the appropriate temperature. If it’s colder than this, the test might show incorrect results, like mistakenly increased signals, delayed response times, or slower nerve signal speeds.
How is Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy performed
Before any tests are done, the doctor will deeply review your medical history, examine your current health and do a thorough physical checkup. This is to help the medical experts understand the condition better, you are currently facing, referred to as AIDP (Acute Inflammatory Demyelinating Polyneuropathy), and to decide the right tests needed for a proper diagnosis.
The doctor, who is conducting the tests, will have a talk with you to explain why the tests are needed. They will clearly lay out the risks and advantages of going through the exam. It’s important that you understand and agree (give consent) to the tests for them to proceed.
The tests generally involve checking at least 3 of your limbs (legs or arms), and involve checking both how your nerves sense different stimuli (sensory nerve conduction studies) and how your muscles function (motor nerve conduction studies and EMG needle testing). These tests cover both the muscles closer to the center of your body (proximal) and further away (distal).
To make sure the recordings from these tests are clear, the doctor will try to minimize any electrical disturbances that can happen during bedside testing using a device called a notch filter. Removing any unnecessary source of noise, like turning off machines not needed for the test or even unplugging the bed if possible, is also part of the process.
Possible Complications of Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy
Just like all tests which involve electrical diagnosis for any medical situation, the chances of experiencing complications are pretty low. However, it’s important to note that there’s always a tiny chance of bleeding, getting an infection, or suffering from nerve damage due to the use of needles in these tests.
What Else Should I Know About Electrodiagnostic Evaluation of Acute Inflammatory Demyelinating Polyneuropathy?
AIDP, or acute inflammatory demyelinating polyradiculoneuropathy, is a condition where your immune system attacks the protective covering of your nerves, known as myelin. Doctors use a variety of tests, including nerve conduction studies, to diagnose this condition.
In nerve conduction studies, small electric shocks are given to the nerve to see how well and fast the nerves can send electrical signals. If AIDP is present, the test might show delays in the time it takes for the nerves to respond to these shocks. This delay is because the nerve’s protective layer, the myelin, is damaged, slowing down the signals.
In addition, the nerves might have a poor ability to send signals along their length, demonstrated by measuring the area of signal response (CMAP). A ratio of less than 0.70 in the area of signal response may indicate the presence of AIDP.
Moreover, some nerves may show increased duration of response indicating possible damage. F-wave studies are particularly informative for AIDP, as these tests can detect inflammation at the nerve roots, which are the parts of the nerve close to the spinal cord.
Finally, a different kind of test, known as needle electromyography, might not show remarkable changes in AIDP unless the nerve’s body, the axon, is involved. Only then would there be signs of active harm to the nerves, such as abnormal spontaneous activity or changes in nerve cell regeneration.