Pain felt in the left shoulder does not always indicate a problem with the shoulder joint or its surrounding muscles. Sometimes, discomfort experienced in one area of the body can actually originate from a completely different location. This phenomenon is known as “referred pain,” where pain signals from an internal organ or distant body part are perceived in a more superficial region, such as the left shoulder.
The Mechanism of Referred Pain
Referred pain occurs because sensory nerves from different body parts connect within the spinal cord. Nerves from internal organs and superficial areas like the shoulder often converge on the same spinal cord segments. This shared pathway can lead the brain to misinterpret the pain signal’s origin. For example, signals from an affected internal organ might travel along a nerve pathway that also carries signals from the left shoulder. The brain, more accustomed to signals from superficial areas, attributes the internal pain to the shoulder.
Cardiac Causes
Heart conditions are a common cause of referred left shoulder pain, as nerves from the heart and left arm are closely linked. A heart attack occurs when blood flow to heart muscle is blocked. This can cause pain or discomfort radiating to the left shoulder, arm, neck, jaw, or back, often with chest pressure, shortness of breath, nausea, and sweating. The pain may feel like tightness, pressure, or squeezing, and typically does not change with position.
Angina, another heart-related condition, also causes referred pain in the left shoulder or arm. It is chest pain or discomfort when the heart muscle doesn’t receive enough oxygen-rich blood, usually due to narrowed coronary arteries. This discomfort can spread to the shoulders, arms, neck, jaw, or back. Angina pain is often triggered by physical exertion or stress and usually subsides with rest or medication within 10 to 20 minutes.
Other Internal Organ Causes
Beyond cardiac issues, various other internal organ problems can cause referred pain in the left shoulder. Irritation of the diaphragm, the muscular wall separating the chest and abdomen, can refer pain to the left shoulder. This happens because the diaphragm’s nerve pathways connect to the same spinal segments that supply sensation to the shoulder. Conditions like gas, inflammation, or abscesses below the diaphragm can trigger this pain.
Problems with the spleen, located in the upper-left abdomen, are another source of referred left shoulder pain. Conditions like splenic rupture, enlargement, or abscess can cause pain in the left upper abdomen that radiates to the left shoulder. This occurs when splenic issues irritate the diaphragm. The pain often worsens when lying flat with elevated legs.
Inflammation of the pancreas, known as pancreatitis, can also lead to referred left shoulder pain. The pain often begins in the upper abdomen and can radiate to the back. This pain may intensify after eating, particularly fatty foods, and can become more severe when lying flat.
Conditions affecting the left lung or pleura, such as pleurisy or pneumonia, may also cause referred pain in the shoulder. Pleurisy, an inflammation of the pleura, presents as sharp chest pain that worsens with deep breathing, coughing, or sneezing, and can spread to the shoulder or back. Esophageal issues like spasms or gastroesophageal reflux disease (GERD) can also cause chest pain that radiates to the left shoulder or arm.
Nerve-Related Causes
Pain perceived in the left shoulder can also stem from issues involving nerves originating from the neck or upper spine. Cervical radiculopathy, commonly termed a “pinched nerve” in the neck, occurs when a nerve root in the cervical spine is compressed or irritated. This compression can cause pain, numbness, or tingling that radiates from the neck down the arm to the shoulder and hand. The pain may be described as burning or sharp and can worsen with certain neck movements.
Injury or compression of the brachial plexus, a network of nerves transmitting signals from the spinal cord to the shoulder, arm, and hand, can also cause referred left shoulder pain. These injuries often result from forceful trauma, such as when the arm is pulled or stretched, leading to pain, weakness, numbness, or loss of movement in the affected areas.
Thoracic outlet syndrome (TOS) is another nerve-related condition that can cause left shoulder pain. This syndrome involves the compression of nerves or blood vessels in the thoracic outlet, the narrow space between the collarbone and the first rib. Symptoms often include pain, tingling, or weakness in the neck, shoulder, arm, and hand. The pain may worsen when lifting the arms, and can be accompanied by numbness or a feeling of coldness in the affected limb.
When to Seek Medical Attention
Experiencing left shoulder pain, especially if it is unexplained or accompanied by other symptoms, warrants medical evaluation. Immediate medical attention is necessary if left shoulder pain is accompanied by chest pain, shortness of breath, dizziness, cold sweats, or nausea, as these can be signs of a heart attack. Sudden, severe pain, or pain that follows a traumatic injury and results in a deformed shoulder or inability to move the arm, also requires urgent care.
Consulting a doctor is advisable for persistent or worsening left shoulder pain, pain that does not improve with rest, or discomfort accompanied by fever, chills, or unexplained weight loss. Seeking professional medical advice ensures an accurate diagnosis and appropriate treatment plan. Relying on self-diagnosis for such symptoms is not recommended due to the diverse and potentially serious underlying causes.