Overview of Electrodiagnostic Evaluation of Critical Illness Myopathy
As medical advancements improve the survival rates of critically ill patients, a complication known as “Intensive Care Unit Acquired Weakness” or ICUAW, is becoming more prevalent. This condition, which often goes undetected, is a range of issues that include critical illness neuropathy (CIN, where nerve damage occurs) and critical illness myopathy (CIM, which involves muscle damage). While pure nerve damage is rare, patients often have a mix of CIN and CIM, or only CIM. Recognizing these conditions and understanding their key features and test results early on is essential to avoid further disabilities and improve patient outcomes. Generally, patients with nerve damage often face long-term impairments, while those with only muscle damage can recover relatively quickly with little lasting effects.
ICUAW is quite common, especially among patients who have been on a mechanical ventilator for more than seven days – studies suggest the occurrence can range from 25% to 83%. Certain risk factors increase the likelihood of developing CIM, including the use of high-dose steroids, neuromuscular blocking agents, experiencing a severe chronic obstructive pulmonary disease (COPD) or asthma episode, and high blood sugar levels.
The causes of CIM are thought to be a mix of microscopic blood vessel changes, metabolic alterations, and electrical disruptions, leading to inflammation. This inflammation, coupled with an increase in muscle breakdown and a decrease in muscle protein synthesis, can result in muscle loss, muscle fiber necrosis, and visible muscle wasting, which could be identified in a muscle biopsy. The level of a muscle protein called creatine kinase could be normal or only temporarily elevated in a patient with CIM.
Worth noting is that steroid myopathy, a muscle weakness condition caused by prolonged steroid use, can mimic CIM symptoms by affecting the same muscles around the hips and shoulders. But steroid myopathies affect a specific type of muscle fiber, known as 2B, so electromyogram (EMG) test results, which measure muscle response, would usually be normal, unlike in CIM.
Why do People Need Electrodiagnostic Evaluation of Critical Illness Myopathy
If a person is seriously ill, they might experience conditions known as critical illness neuropathy and critical illness myopathy. These conditions commonly show up in the form of difficulty getting away from a ventilator, which is a machine that helps with breathing. If a person is taken off the ventilator, they might feel very weak, their arms and legs may feel limp, and their natural reflex response to stimuli might be weaker.
Critical illness myopathy often shows up as weakness closer to the center of the body. This can be observed during a manual muscle strength test, which could reveal weak shoulder and hip muscles. Despite this weakness, sensory reflexes aren’t typically affected, meaning their sense of touch would remain unaltered. The muscles controlling the eyes, face and most worryingly, the diaphragm, which is essential for breathing, can be affected. However, it’s noteworthy that the muscles in the throat area (bulbar muscles) and automatic physical responses (autonomic instability) aren’t typically impacted. These findings can help exclude certain other conditions that affect the link between nerves and muscles, and muscle diseases from the list of potential diagnoses.
Complications in weaning away from a ventilator often arise due to the involvement of the diaphragm or other muscles that assist in breathing. It’s important to note that changes caused by nerve damage, termed Wallerian degeneration, might only become apparent after at least 14 days following injury. So, any tests to assess such changes should ideally be conducted about two weeks after symptoms first show up, and mainly in patients who are more likely to have such issues.
When a Person Should Avoid Electrodiagnostic Evaluation of Critical Illness Myopathy
Doing electric-based tests on very ill patients does not have many complete restrictions. However, a test called needle EMG should not be done on people with serious blood disorders that cause a lot of bleeding. The needles used for this test should also never be used on areas of the body with an active infection. Another type of test, nerve conduction studies, should not be performed on people with implanted heart rhythm control devices, or connected to external ones. It’s important for patients to be checked for pacemakers – electrical devices that control the heart rate – and the electric stimulation during the testing should not be done directly on or too close to the device.
How is Electrodiagnostic Evaluation of Critical Illness Myopathy performed
Before any tests are done, your doctor needs to do a complete check-up and understand your past medical history. They will also talk with you and your family about the tests, what they’re for, and how they will be done. One specific test used to diagnose CIM, a type of muscle weakness, involves checking at least three limbs. This test looks at both sensation (how you feel) and motor skills (how you move), and uses a needle EMG test in various muscles for comparison.
It’s important for your limbs to be warm during the test because cold can influence the results, making them appear abnormal. The testing environment matters a lot too – to reduce any electrical interference that could skew results, some equipment in the ICU might need to be turned off, including the hospital bed, while the test is going on.
Possible Complications of Electrodiagnostic Evaluation of Critical Illness Myopathy
Like all tests that use electricity to diagnose health conditions, the chance of having complications is small. There’s always a small possibility of bleeding or getting an infection from the needles used during these tests.
What Else Should I Know About Electrodiagnostic Evaluation of Critical Illness Myopathy?
There are two illnesses that can happen when you’re very sick: condition known as Critical Illness Neuropathy (CIN) and Critical Illness Myopathy (CIM). Both of these illnesses affect your muscles and nerves, but they do so differently.
CIN mainly affects the protective covering (axonal) of the nerve cells that carry messages (sensorimotor peripheral neuropathy) between the brain and the body. CIM generally leaves the nerves alone but directly impacts the muscles.
There’s a type of checkup called an Electromyography (needle EMG) that helps doctors to tell these two diseases apart. If you have CIM and not CIN, this test will show some unusual results, much like those seen in other diseases that primarily affect the muscles.
Since CIM doesn’t usually affect the sensory fibers (that help us feel things), the tests that measure how well these sensory fibers are working (sensory nerve conduction studies) will indicate normal results. However, if these tests don’t show normal results, it might suggest that you have CIN in addition to CIM.
Also, CIM doesn’t usually affect the function of motor nerves which control our muscles movement, so tests that measure how these nerves are working (motor nerve conduction studies) should also come out generally normal. In severe CIM cases, where you might experience significant wasting of the muscles, these test results might show a slight decrease.
By conducting an EMG using a needle, doctors can find unusual patterns in muscles when they’re resting. Specifically in the muscles that are closer to the center of the body (proximal muscles) rather than those farther from it (distal muscles). These abnormalities can also be found in the diaphragm muscle, the main muscle responsible for breathing.
