Overview of Electrodiagnostic Evaluation of Critical Illness Neuropathy
As healthcare improves, more people who are very sick are living longer after they go to the hospital, specifically to the intensive care units (ICUs). Certain people, such as those with infection throughout the body (sepsis), multiple failing organs, severe burns, who are on breathing machines for a long time, or those taking multiple medications, can develop severe muscle weakness during their hospital stay, even if they’re getting the right treatments. This is usually known as “ICU-acquired weakness” (ICUAW). This condition usually happens because of a combination of two conditions: critical illness polyneuropathy (CIP) and/ or critical illness myopathy (CIM). CIP affects the nerves and CIM affects the muscles.
Often, both of these conditions can be overlooked. However, studies suggest that between 25% to 83% of people on a breathing machine for a week or longer may get ICUAW.
Critical Illness Neuropathy (CIN), another name for CIP, can be seen as a patient having a hard time coming off the breathing machine or if the patient has extreme weakness or numbness in their arms and legs when sedation wears off. A physical exam might also show weaker natural muscle reflexes, potential muscle shrinking, or problems with balance when the patient leaves the ICU. The muscles that regulate swallowing and eye movement are often not affected in CIP.
Tests such as a liquid test from the brain and spinal cord can help differentiate it from other similar conditions, such as Guillain-Barre Syndrome. The level of a protein called Creatine phosphokinase, which can show if muscles are damaged, is usually normal in CIP but can increase in CIM. The most common cause of CIP is systemic inflammatory response syndrome (SIRS) or sepsis – this is different from CIM where the use of muscle paralyzing agents and steroids are more prevalent.
To confirm a diagnosis of CIP, nerve conduction studies and needle electromyography (tests that study electrical activity of nerves and muscles) are often used, but it can be hard to perform them in ICU conditions due to things like electrical interference or the patient’s condition. It’s still an essential tool to evaluate severe weaknesses in ICU settings and helps in making treatment plans.
The causes of both CIP and CIM are not fully understood, but they are believed to be complex and multifactorial, meaning they involve a variety of factors. The conditions cause nerve damage, reduced blood flow to the nerves, and nerve breakdown, necessitating treatment of underlying medical causes and physical neuro-rehabilitation.
The cause is believed to involve changes to blood flow, metabolism (chemical reactions in the body), and electrical activity in the nerve cells leading to problems with the motor or sensory nerve cells. These changes can be increased blood flow into the tissues causing swelling, low oxygen in the tissues, invasion of inflammation causing cells, blockage within the units containing muscles and nerves; production of harmful particles from oxygen and nitric oxide, damage to the energy producing part of cells, damage to nerves because of high sugar in the body, and protein deficiency; disruption of sodium and calcium channels and loss of cell excitability.
Patients can exhibit a range of symptoms due to CIP including muscle weakness or paralysis (more in the lower limbs compared to the upper limbs), marked decrease in muscle bulk or mild wasting, early loss of deep tendon reflexes, and difficulty weaning off mechanical ventilation with exclusive cause of heart or lung problems.
On the other hand, CIM can be seen in patients who’ve had exposure to muscle paralyzing agents, severe asthma, pneumonia, prolonged period of low pH in the body, lung injury leading to respiratory distress, prolonged use of steroids, long term use of aminoglycosides, sepsis, multiorgan failure, and organ transplantation. Muscle weakness or paralysis (more in the upper limbs compared to lower limbs), delayed loss of deep tendon reflexes, and difficulty weaning off ventilation with exclusive cause of heart or lung problems are generally noticed.
In both cases, to further aid the diagnosis, a biopsy of the muscle tissues may be performed.
Why do People Need Electrodiagnostic Evaluation of Critical Illness Neuropathy
People with either critical illness neuropathy (a condition affecting the nerves) or myopathy (a disease of the muscles) may struggle to get off a ventilator, a machine that helps them breathe. After removing the ventilator, they might experience severe weakness and their arms or legs may feel very limp.
People with critical illness neuropathy might also have trouble sensing things. They may feel numb or experience strange sensations (known as paresthesias), especially in their hands and feet, which are located furthest away from the center of the body.
The problems with coming off the ventilator are due to the fact that critical illness neuropathy and myopathy can affect the phrenic nerve. This nerve controls the diaphragm, a muscle that helps you breathe, and other muscles that help with breathing can be affected too.
It can take 10 to 14 days for Wallerian degeneration (the sequence of events when a nerve fiber is cut or crushed) to show up on an electrodiagnostic test, a procedure to test the health of muscles and nerves. Therefore, doctors should be careful about who they order these tests for. They usually do it only for patients who really need it, and generally about two weeks after symptoms first appear.
When a Person Should Avoid Electrodiagnostic Evaluation of Critical Illness Neuropathy
Some tests, such as electrodiagnostic studies, may not be suitable for seriously ill patients in certain circumstances. Electrodiagnostic studies look at how well the nerves and muscles in the body work.
One of these tests, called needle electromyography (EMG), involves inserting small needles into the muscles. This isn’t safe if a person has severe bleeding disorders. The needles should also not be put into parts of the body where there is an active infection.
Another type of electrodiagnostic study is a nerve conduction study. This test is not safe for people with implanted heart defibrillators (devices that help control irregular heartbeats) or those connected to external defibrillators. For safety reasons, anyone having this test should be asked if they have a pacemaker, and no electrical stimulation should be applied around the area where the pacemaker is placed.
How is Electrodiagnostic Evaluation of Critical Illness Neuropathy performed
Before any tests are carried out, the medical team needs to understand the patient’s medical history, current health status, and carry out a thorough physical examination. It’s crucial that the doctor explains the purpose and process of these tests to the patient and their family. To accurately diagnose CIN, which is a condition that affects the nerves, the medical team carries out tests on at least three different parts of the body, including both upper and lower body parts for comparison.
During these tests, it is important that the patient’s body – particularly their limbs – is warm. This is because cold can affect the results of the tests, increasing some readings and slowing down nerve responses. To reduce any electrical interference in the room, which can affect the equipment, a special filter should be used. Unnecessary electrical devices, including the hospital bed, should also be turned off if possible.
Possible Complications of Electrodiagnostic Evaluation of Critical Illness Neuropathy
When undergoing electrodiagnostic studies, which are tests used to evaluate the electrical activity of the muscles and nerves, there is generally a very low chance of facing complications. However, like with most medical procedures involving needles, there is a small risk that the area where the needle was inserted could bleed or get infected.
What Else Should I Know About Electrodiagnostic Evaluation of Critical Illness Neuropathy?
Critical illness neuropathy is a condition affecting the peripheral nerves, which are the ones outside your brain and spinal cord. It affects your senses and motor skills – the ways your body moves. It’s particularly noticeable in tests that measure nerve and muscle function (electrodiagnostic studies). Your nerves and muscles farthest from your center (distal) are more impacted than those closer (proximal).
Two forms of neuropathy, CIP and CIM, are tough to tell apart. Patients who are awake and can stand an electromyography test (EMG) – a way to evaluate muscle and nerve function – may have their muscle activity measured. Occasionally, only the senses are affected, which can help identify the condition. A muscle biopsy is another way to tell the symptoms apart by looking for signs of muscle damage in a sample.
A nerve conduction study is one type of electrodiagnostic test that examines the speed and intensity of electrical signals through your nerves. Two main types of these studies, sensory and motor, are usually performed.
In a sensory nerve conduction study, the strength of the signal (conduction amplitude) is reduced, and there’s often no response to the stimulus (absence of sensory nerve conduction studies, or SNAPs). At first, signals often travel at near-normal speeds and experience little delay, but the strength of the signals can decrease significantly.
Motor nerve conduction studies, which examine the nerves that control your muscles, show similar results: lower signal strength and sometimes an absence of muscle responses (compound muscle action potentials, or CMAPs). Signal speed and delay don’t change much, but the signal strength reduces significantly, typically by twice the standard deviation – a measure of variation.
Another form of testing, needle electromyography, measures the electrical activity in your muscles using a thin needle. It can identify any abnormal muscle responses, such as “positive sharp waves” or “fibrillation potentials”. These terms describe different patterns of electrical activity that suggest muscle damage. This test can also measure how the motor units – the nerves and the muscles they control – are working. It can also be used to test the diaphragm, the muscle that controls breathing.
A doctor can diagnose CIP and CIM based on the results of these tests. Each condition has a pattern of results that can help distinguish one from the other.
