What is Phrenic Nerve Injury?
The phrenic nerve is one of the most critical nerves in our body because it plays a major part in breathing. It provides the main muscle control to the diaphragm, which is the muscle that we primarily use for breathing. An injury to the phrenic nerve, such as from chest and heart surgery, can lead to diaphragm paralysis or malfunction. The symptoms of a phrenic nerve injury are not specific, meaning it can be hard to diagnose. However, there are several ways to identify a phrenic nerve injury, including ultrasound, electromyography (a test that measures muscle response), and fluoroscopy (a type of imaging that shows moving body structures).
Ultrasound is becoming a preferred way to diagnose this condition because it’s easy to use, doesn’t expose the patient to radiation, is low cost, can be done right at the patient’s bedside, and can be done again easily if needed. This makes it particularly useful for severe cases. It’s becoming more popular to use ultrasound to check for phrenic nerve injuries because it can assess the diaphragm’s function and structure. Diaphragm ultrasound can help doctors identify diseases caused by phrenic nerve injury, including diaphragmatic paralysis and dysfunction. It can sometimes even find the cause behind the disease and give information needed to determine the patient’s prognosis (expected outcome). This test is also helpful in evaluating prolonged use of mechanical ventilation and difficulty weaning off mechanical ventilation. It can also help identify patients who may benefit from early surgical treatment (called plication) which can reduce hospital stays and risks of ventilator-associated pneumonia (lung infection).
What Causes Phrenic Nerve Injury?
The phrenic nerve can be harmed in several ways. Surgery, particularly around the chest and heart, is a frequent cause. The left phrenic nerve is located just in front of the pericardium (the sac that holds your heart) and the mediastinal pleura (part of the inner lining of your chest). So, it’s at risk when operating near a blood vessel in your chest called the internal thoracic artery. One major risk during heart operations is the very cold slurry used to keep the heart safe.
The phrenic nerve can also be damaged from blunt or sharp injuries, diseases like diabetes, infections including Lyme disease and shingles, direct invasion by tumors, and nervous system disorders such as cervical spondylosis (degeneration of the spine in your neck) and multiple sclerosis. Other causes include muscular dystrophy (a group of diseases that makes your muscles weaker) and Guillain-Barre syndrome, which is a condition where your immune system attacks your nerves.
If the phrenic nerve is damaged, it can cause issues with your diaphragm, the muscle that helps you breathe. This can come as diaphragm dysfunction or paralysis on one or both sides. Paralysis on one side often happens because of treatment-related complications. When both sides are paralyzed, it’s mostly due to motor neuron disease, which includes conditions like amyotrophic lateral sclerosis (a type of motor neuron disease that affects nerve cells in the brain and spinal cord) and post-polio syndrome, a condition that affects polio survivors years after recovery from an initial acute attack of the poliomyelitis virus.
Risk Factors and Frequency for Phrenic Nerve Injury
Research has indicated that diaphragmatic paralysis, a condition affecting the muscle that helps in breathing, is more common in males. One of these studies found that between 1% and 7% of people with severe blunt force trauma have a diaphragmatic injury. Additionally, up to 3% of abdominal injuries also affect the diaphragm.
Signs and Symptoms of Phrenic Nerve Injury
A phrenic nerve injury is a condition that can be challenging to diagnose because the symptoms can be pretty general. Such symptoms may include hard-to-explain shortness of breath, recurrent pneumonia, anxiety, insomnia, fatigue, headaches when you wake up, excessive sleepiness during the day, and difficulty getting off artificial breathing support in hospital settings. Often, an individual with one-sided paralysis of the diaphragm, can still feel okay when at rest, only experiencing breathing difficulties with physical activities. This type of paralysis is usually stumbled upon in a chest X-ray. In contrast, people with paralysis in both sides of the diaphragm always experience shortness of breath.
A physical examination might reveal quieter breath sounds on the affected side, a dull sound when the affected side of the chest is tapped, and the unusual inward movement of the upper abdomen when drawing breath.
Testing for Phrenic Nerve Injury
Testing for damage to the phrenic nerve, which controls the diaphragm, can be done through several methods, such as measuring pressure in your esophagus and stomach, studying the electrical activity in your diaphragm, or an ultrasound, which uses sound waves to create images of the body. The ultrasound of your diaphragm, the muscle that helps you breathe, is generally done with a low-frequency probe.
For viewing in between your ribs, a high-frequency probe is better because it’s smaller and can fit into those tight spaces.
These tests usually require patients to lie flat on their back (the supine position) while breathing normally. This position is important because it prevents the muscles in the front part of your abdomen from helping you to exhale, which might hide paralysis.
In the ultrasound results, your diaphragm will appear as a thick, bright line. The left part of your diaphragm can be studied through a view that includes the spleen while the right part is observed through a view that includes the liver. Interestingly, if you have conditions like a large mass in the upper left part of your abdomen, an enlarged spleen or liver, it could actually make your diaphragm easier to evaluate. One sign of diaphragm paralysis is when it doesn’t move as it should or moves in the opposite direction.
Another way doctors assess your diaphragm is by measuring its thickness during breathing. This is typically done using the high-frequency ultrasound probe, placed along your side between your lower ribs. This area is also referred to as the Zone of Apposition (ZOA). Measuring the thickness of the diaphragm helps to check for muscle wasting, particularly in patients on ventilators.
At the end of breathing out, diaphragm thickness less than 0.2 cm is considered indicative of muscle wasting. Usually, the average thickness of a healthy diaphragm is between 0.22 to 0.28 cm. However, in a paralyzed diaphragm, the thickness is often less, between 0.13 to 0.19 cm. The proportion of the diaphragm thickness change (Thickening Fraction) can also help predict the patient’s ability to breathe on their own after being taken off a ventilator.
Treatment Options for Phrenic Nerve Injury
If you’re diagnosed with diaphragmatic paralysis but aren’t experiencing any symptoms, you probably won’t need treatment. If a specific cause can be identified, such as an underlying disease, the best course of action is to treat that directly. However, sometimes, simply treating the root cause is not enough and some people continue to have symptoms. This is also the case for people who have diaphragmatic paralysis on both sides of their diaphragm.
In these situations, there are several surgical treatments to consider. One method is called plication, a surgery where the affected area of the diaphragm is folded and sewn together to reduce its size and help you breathe more easily. This method is particularly helpful for patients who have been relying on help from a ventilator to breathe. Plication is most effective for individuals who have a one-sided diaphragmatic paralysis and are not severely overweight.
An alternative treatment is phrenic nerve stimulation. This is a procedure that stimulates the phrenic nerve, which controls the diaphragm, improving its function. This procedure is an option for people with paralysis of both sides of the diaphragm caused by injuries to the cervical spine -the upper part of the spine that supports the neck. But it can only be done if the phrenic nerve is still intact and the muscles it corresponds to are not suffering from a disease that weakens them (myopathy).
What else can Phrenic Nerve Injury be?
If you are experiencing symptoms of a phrenic nerve injury, such as shortness of breath, doctors will need to consider a variety of potential causes. These could be related to your lungs (pulmonary), heart (cardiac), the chemical reactions in your body (metabolic), or your blood (hematologic). If you have a specific condition known as bilateral diaphragmatic paralysis, physicians will need to look into a few more possibilities:
- Diseases affecting the cells at the front of your spinal cord (anterior horn cells)
- Diseases affecting the connection points between your nerves and muscles (neuromuscular junction diseases)
Another tricky condition to differentiate is hypoventilation caused by a cervical spine disease, which can appear very similar to a problem with your phrenic nerve.
What to expect with Phrenic Nerve Injury
The seriousness and outcome of a phrenic nerve injury, which can result in diaphragmatic paralysis, depends on the root cause and overall lung health of the patient. As a general rule, if only one side of the diaphragm is paralyzed, the prognosis, or likely outcome, is quite good unless the patient is suffering from severe shortness of breath. Patients who experience a bilateral diaphragmatic paralysis, meaning paralysis on both sides, can recover, but it usually takes more than a year for partial or complete recovery.
