The phrenic nerve is an internal structure that controls the diaphragm, the primary muscle responsible for breathing. There are two nerves, one on the right and one on the left, each controlling one side of the dome-shaped diaphragm. Its main function is to send a continuous signal that causes the diaphragm to contract and flatten, creating the negative pressure needed to draw air into the lungs. Beyond its motor function, the nerve also carries sensory fibers from the diaphragm and the surrounding linings of the lungs and heart. When this nerve becomes irritated, it can cause pain that is often confusingly located far from the actual source.
The Specific Sensation of Phrenic Nerve Pain
Phrenic nerve irritation often manifests as a sharp, stabbing sensation that can feel deeply internal. The pain may also be described as a deep, persistent ache or a burning discomfort, often fluctuating in intensity from mild to severe. It is typically intermittent, sometimes presenting as sudden, involuntary spasms or jolts of discomfort in the chest or upper abdomen.
The sensation frequently intensifies with movements that cause the diaphragm to stretch or contract forcefully. A deep breath, for instance, can sharply increase the pain as the inflamed nerve is pulled or compressed. Simple actions like coughing, sneezing, laughing, or bending and twisting the torso can trigger a painful response because they engage the diaphragm.
The pain can sometimes mimic other, more common conditions, making it difficult to pinpoint the source. Because the diaphragm is active with every breath, the discomfort can feel like it is linked to the lungs or heart, even when the underlying issue is solely nerve irritation. This quality of pain is tied to the sensory fibers of the nerve that detect discomfort in the diaphragm and the membranes surrounding nearby organs.
Understanding Referred Pain Pathways
A defining characteristic of phrenic nerve pain is its tendency to be felt in a location far removed from the diaphragm. This phenomenon, known as referred pain, occurs because the phrenic nerve originates high in the neck from the cervical spinal nerves C3, C4, and C5. These same nerve roots also supply sensory input to the skin and muscles of the neck and shoulder region.
When the phrenic nerve is irritated near the diaphragm, the signal travels up to the spinal cord and converges with signals from the neck and shoulder. The brain misinterprets the origin of this incoming pain signal, perceiving the discomfort as coming from the more familiar neck or shoulder area, rather than the internal diaphragm. The most common location for this referred pain is the tip of the shoulder, a symptom sometimes called Kehr’s sign when related to irritation below the diaphragm.
The pain may also be felt along the upper trapezius muscle or at the base of the neck, corresponding to the C3-C5 dermatome areas. For example, irritation of the diaphragm on the right side, perhaps from a liver issue, may cause pain in the right shoulder tip. This anatomical overlap means a problem deep within the chest or abdomen can present as seemingly unrelated shoulder or neck pain.
Common Causes of Phrenic Nerve Irritation
Irritation of the phrenic nerve can stem from a variety of sources, many involving direct pressure or inflammation in the chest or abdominal cavity. A frequent cause is trauma or irritation following abdominal or thoracic surgery. Laparoscopic procedures, such as gallbladder removal, often require the inflation of the abdominal cavity with carbon dioxide gas. This insufflation can stretch or chemically irritate the diaphragm and the nerve endings, leading to temporary referred shoulder pain post-operation.
Physical compression is another common trigger, which can happen due to tumors growing in the chest cavity or from enlarged lymph nodes. Structural issues like a diaphragmatic hernia, where an organ pushes through the diaphragm, can also place sustained pressure on the nerve. Inflammation of nearby structures can also cause irritation, including:
- Pleurisy (inflammation of the lung lining).
- Pericarditis (inflammation of the sac around the heart).
- Neuralgic amyotrophy, an inflammatory process that targets nerves.
- Infections, such as certain viruses.
In all these scenarios, the underlying mechanism involves either direct mechanical pressure or chemical inflammation affecting the nerve.
Next Steps and When to Consult a Doctor
Any persistent or severe pain located in the shoulder or neck, especially if accompanied by breathing difficulties, warrants a medical evaluation. While mild discomfort from temporary irritation may resolve on its own, a doctor needs to rule out more serious underlying causes. Prompt medical attention is important if the pain is accompanied by certain “red flag” symptoms.
These concerning signs include:
- Shortness of breath or an inability to take a deep breath.
- Breathlessness that worsens when lying down (orthopnea).
- Unexplained chronic fatigue.
- Recurrent pneumonia or signs of sleep-disordered breathing like new or severe snoring.
A medical professional will perform a physical exam and may order imaging, such as a chest X-ray or CT scan, to evaluate the diaphragm’s position and movement. Specialized tests like nerve conduction studies or electromyography may also be used to assess the nerve’s function and confirm a diagnosis.