Pneumonia can cause pain in the shoulder, but this is an indirect symptom rather than a problem with the shoulder joint itself. The discomfort arises from inflammation spreading to structures near the lungs. This unexpected connection is a form of referred pain, where the brain misinterprets signals originating in the chest or abdomen. Understanding this requires looking at the shared nerve pathways between the torso and the shoulder area.
How Lung Inflammation Causes Shoulder Discomfort
Pneumonia is an infection that inflames the air sacs in the lungs, which can lead to a complication called pleurisy, or inflammation of the pleura. The pleura consists of two layers of tissue surrounding the lungs and lining the inner chest wall. When these layers become inflamed, they rub against each other, causing sharp chest pain that intensifies with movement, coughing, or deep breaths.
This inflammation can spread to irritate the diaphragm, a dome-shaped muscle separating the chest cavity from the abdomen and functioning as the primary muscle for breathing. Irritation of the diaphragm, especially its central part, initiates the sensation of pain in the shoulder. When pneumonia affects the lower lobes of the lungs, it is more likely to cause this diaphragmatic irritation due to its proximity to the muscle. The diaphragm’s movement causes friction against the inflamed tissue, leading to persistent irritation that is then perceived elsewhere in the body.
The Mechanism of Referred Pain
Irritation in the chest is felt in the shoulder due to a neurological process known as referred pain. This concept describes discomfort that is perceived in one location, even though the actual cause lies in a different part of the body. The connection is made through the phrenic nerve, which controls and provides sensation to the diaphragm.
The phrenic nerve originates in the neck from the C3, C4, and C5 spinal nerve levels. These same spinal segments also supply sensory nerves to the skin and tissues around the shoulder and neck area. Because the phrenic nerve and the nerves supplying the shoulder share a common origin point in the spinal cord, the brain can become confused. It receives a strong signal of irritation traveling along the shared pathway and incorrectly projects the sensation to the shoulder. The resulting pain is typically felt on the same side as the lung infection, often around the shoulder blade or tip of the shoulder.
Identifying Pneumonia-Related Shoulder Pain
Distinguishing referred pain from a musculoskeletal injury is important for proper diagnosis. Shoulder pain caused by pneumonia, or pleurisy, has distinct characteristics that differ from a common strain or tendon issue. A defining feature is that the discomfort usually does not worsen when the shoulder joint itself is moved, such as raising or rotating the arm. In a muscular injury, movement of the joint would typically increase the pain.
The pain is specifically aggravated by actions that involve the diaphragm and lungs, such as taking a deep breath, coughing, or sneezing. This discomfort is often described as sharp or stabbing and can be localized to the shoulder blade area or the top of the shoulder. This referred shoulder pain is almost always accompanied by the common symptoms of pneumonia, including fever, a persistent cough, chills, and shortness of breath. The presence of these respiratory signs alongside shoulder pain strongly suggests an underlying lung process rather than a simple orthopedic problem.
When to Seek Medical Evaluation
Any unexplained shoulder pain that is not clearly related to an injury, or that is accompanied by respiratory symptoms, warrants prompt medical attention. If shoulder pain is sharp and increases when you take a deep breath or cough, it should not be dismissed as a simple muscle ache. Pneumonia is a serious infection that requires diagnosis, usually through a chest X-ray, and treatment, which typically involves antibiotics for bacterial cases.
Self-diagnosing is not recommended, as only a medical professional can determine if the pain is referred from the lungs or is musculoskeletal in origin. Seeking timely evaluation is important when symptoms include fever, difficulty breathing, or coughing up blood. These can indicate a rapidly worsening infection or other serious conditions like a pulmonary embolism.