Phrenic nerve damage is most commonly caused by surgical injury, particularly during heart and chest procedures, but it can also result from trauma, infections, nerve inflammation, spinal cord injuries, and tumors pressing on the nerve. The phrenic nerve originates from the C3 through C5 spinal nerve roots in the neck and travels a long path through the chest to reach the diaphragm, making it vulnerable to injury at multiple points along the way. Because this nerve is the sole motor supply to the diaphragm, damage to it can partially or fully paralyze the body’s primary breathing muscle.
What the Phrenic Nerve Does
The phrenic nerve carries motor, sensory, and sympathetic fibers from the neck down through the chest, passing near the heart and lungs before reaching the diaphragm. Its main job is telling the diaphragm to contract during each breath. When it fires, the diaphragm flattens downward, expanding the chest cavity and pulling air into the lungs. It also carries pain and touch signals from the lining around the heart (the pericardium) and the tissue lining the inner chest wall. This is why some people with phrenic nerve irritation feel pain referred to the shoulder, since the nerve shares spinal roots with nerves that supply the shoulder area.
Cardiac and Thoracic Surgery
Heart surgery is one of the most well-documented causes of phrenic nerve damage. The nerve runs right alongside the heart, so it can be stretched, compressed, or cut during procedures like bypass grafting and valve replacements. A prospective clinical study found that left phrenic nerve conduction was completely absent three weeks after surgery in 8% of bypass patients and 18% of valve replacement patients.
Cold injury plays a major role. Surgeons often use ice slush packed around the heart to protect it during surgery, and this direct cold exposure can damage the nearby phrenic nerve. The same study concluded that hypothermic cardiopulmonary bypass combined with ice slush application around the heart was responsible for phrenic nerve injury in these cases. Lung surgery, esophageal procedures, and surgeries on structures in the central chest also carry risk, since the nerve passes through that corridor.
Nerve Blocks and Anesthesia Procedures
A surprisingly common cause of temporary phrenic nerve paralysis is the interscalene nerve block, a type of regional anesthesia used for shoulder surgery. Because the phrenic nerve originates from the same spinal roots targeted by this block (C3 to C5), the anesthetic frequently spreads to the phrenic nerve as well. Temporary paralysis of the diaphragm on the injected side has been reported in up to 100% of patients receiving this block. For most people, this wears off as the anesthetic fades. In rare cases, however, the paralysis persists, as documented in reports of permanent diaphragm paralysis after total shoulder replacement.
Ultrasound-guided injection techniques have improved precision, allowing smaller medication volumes and more targeted delivery, which may reduce the risk. Still, anyone with existing lung disease or compromised breathing on the opposite side faces higher risk from even temporary diaphragm paralysis on one side.
Trauma and Spinal Cord Injuries
Because the phrenic nerve roots emerge from the C3 through C5 levels of the spinal cord, injuries to the cervical spine can knock out phrenic nerve function. A spinal cord injury above C3 can eliminate signals to both phrenic nerves, making the person unable to breathe without a ventilator. Injuries at C3, C4, or C5 can damage the nerve roots directly, leading to progressive wasting of the diaphragm muscle on the affected side.
Blunt trauma to the neck or chest, such as from car accidents, falls, or stab wounds, can also stretch or sever the phrenic nerve along its path. Birth injuries during difficult deliveries occasionally damage the nerve in newborns, particularly when excessive traction is applied to the neck. Case reports show that even traumatic phrenic nerve injuries can sometimes recover spontaneously, though the timeline can be long. One documented case of traumatic phrenic nerve palsy took 31 months to fully resolve with conservative management alone.
Infections
Several infections can target the phrenic nerve. Lyme disease, caused by the bacterium Borrelia burgdorferi, can invade both the central and peripheral nervous systems, causing a wide range of neurological problems including cranial nerve palsies, meningitis, and nerve root inflammation. Phrenic nerve involvement is rare but real: only 16 cases have been reported in the medical literature, presenting as unexplained shortness of breath from diaphragm paralysis. Lyme-related phrenic nerve palsy can affect one or both sides and may appear without a predictable timeline after the initial infection.
Herpes zoster (shingles) can also damage the phrenic nerve when the virus reactivates along the C3 to C5 nerve roots. Other viral infections, including those caused by certain respiratory viruses, have been linked to phrenic nerve inflammation in isolated reports.
Neuralgic Amyotrophy
Neuralgic amyotrophy, also called Parsonage-Turner syndrome, is an inflammatory condition that attacks peripheral nerves, most often in the shoulder and upper arm. It typically begins with severe pain in the neck and shoulder, followed days to weeks later by muscle weakness. While it primarily hits the brachial plexus (the nerve network supplying the arm), it can also involve the phrenic nerve. When it does, the diaphragm weakens on the affected side, and patients develop shortness of breath that may not be immediately connected to the earlier shoulder pain. The condition is poorly understood and likely involves an immune-mediated attack on the nerve.
Tumors and Compression
Tumors in the chest, neck, or mediastinum (the central compartment between the lungs) can compress or invade the phrenic nerve. Lung cancer is one of the more common culprits, particularly tumors near the hilum where the nerve passes close to major airways and blood vessels. Lymphomas, thyroid tumors extending into the chest, and metastatic cancers can all affect the nerve. In some cases, phrenic nerve paralysis is the first sign that leads to a cancer diagnosis, discovered when a chest X-ray shows an elevated diaphragm on one side.
Symptoms of Phrenic Nerve Damage
When one phrenic nerve is damaged, you may notice shortness of breath during exertion, difficulty taking deep breaths, or trouble sleeping flat on your back. Many people with unilateral (one-sided) damage can compensate reasonably well using their other breathing muscles and the healthy side of their diaphragm, so symptoms can be subtle at first.
Bilateral damage is far more serious. When both phrenic nerves stop working, the diaphragm is essentially paralyzed, and breathing becomes critically dependent on the smaller accessory muscles in the neck and between the ribs. Lying flat becomes especially difficult because gravity pushes the abdominal organs upward against the non-functioning diaphragm, further reducing lung volume. One clinical case documented a patient’s vital capacity dropping from 2.13 liters while sitting to just 0.9 liters when lying down. This dramatic worsening of breathlessness in the supine position, called orthopnea, is a hallmark of diaphragm paralysis.
How It’s Diagnosed
Phrenic nerve damage is often first suspected on a chest X-ray that shows one side of the diaphragm sitting higher than expected. Ultrasound has become an important diagnostic tool because it can visualize the diaphragm in real time. By measuring how much the diaphragm thickens during a breath, clinicians can assess whether the muscle is actively contracting. A healthy diaphragm thickens substantially during inhalation. A paralyzed diaphragm stays thin and may even move upward (paradoxically) when you breathe in. Nerve conduction studies, which send a small electrical signal along the phrenic nerve and measure the diaphragm’s response, can confirm whether the nerve itself is conducting signals properly or has been damaged.
Treatment and Recovery
Treatment depends on the cause, severity, and whether one or both nerves are affected. When the underlying cause is reversible, such as inflammation from an infection or a nerve block that hasn’t worn off, the approach is often watchful waiting while the nerve heals. Recovery timelines vary widely. Some people regain function within weeks, while others take months or even years. Extended conservative management can work even in traumatic cases, though there’s no guarantee.
Inspiratory muscle training is an effective conservative option for people with one-sided diaphragm dysfunction. A randomized trial found that six months of twice-daily breathing exercises against resistance significantly improved breathlessness during activity, exercise tolerance, and inspiratory muscle strength compared to a sham training group. The benefits came not from restoring the paralyzed diaphragm itself but from strengthening the other breathing muscles to compensate more effectively.
For people with high spinal cord injuries or permanent bilateral phrenic nerve damage, diaphragm pacing systems can provide an alternative to full-time mechanical ventilation. These surgically implanted devices stimulate the phrenic nerve or diaphragm directly, triggering regular contractions that mimic natural breathing. The FDA has approved one such system for adults with ALS who still have a stimulatable diaphragm and haven’t lost too much lung function. Nerve grafting and surgical reconstruction are options in select cases where the nerve has been severed or severely damaged, though outcomes depend on how quickly surgery is performed and how much the diaphragm muscle has atrophied in the meantime.