Left shoulder pain is a frequent complaint with a wide range of potential origins, from minor muscle strains to serious internal conditions. The shoulder joint’s complex anatomy, comprising tendons, ligaments, nerves, and muscles, makes it susceptible to localized injuries. However, pain in the left shoulder can also originate from a distant organ or a compressed nerve in the neck. Understanding these distinct categories of pain sources is the first step toward identifying the cause and determining the appropriate course of action.
Localized Musculoskeletal Sources of Pain
The most common causes of left shoulder discomfort involve structures directly within the joint complex, primarily the four muscles and tendons of the rotator cuff. Rotator cuff tendinitis is an inflammation often resulting from repetitive overhead motions or age-related degeneration. This causes a dull ache, particularly when lifting the arm or sleeping on the affected side. If tendon damage progresses, it can result in a partial or complete rotator cuff tear, causing significant weakness and sharp pain with movement.
Another frequent localized cause is bursitis, the inflammation of the bursa, a small, fluid-filled sac that cushions bones and soft tissues. Subacromial bursitis is common in the shoulder, causing pain when the arm is raised overhead. This occurs as the inflamed sac is compressed beneath the acromion, the bony roof of the shoulder. The pain is often described as a constant, deep ache that worsens with specific movements.
Arthritis represents a deterioration of the joint itself. Osteoarthritis causes the gradual wear-and-tear of protective cartilage, resulting in stiffness, a grinding sensation, and pain that worsens with activity. Adhesive capsulitis, commonly known as frozen shoulder, is a separate issue involving the thickening and tightening of the connective tissue capsule surrounding the joint. This condition progresses through painful, stiffening, and thawing stages, severely restricting the range of motion.
Referred Pain from Internal Organs
A less common but potentially severe cause of left shoulder pain is referred pain, where a problem in an internal organ is felt at a distant location like the shoulder. This phenomenon occurs because visceral sensory nerves from internal organs and somatic sensory nerves from the shoulder converge onto the same neurons in the spinal cord. The brain misinterprets the signal, attributing the pain to the shoulder rather than the actual visceral origin.
The most serious example of referred pain to the left shoulder is myocardial ischemia, such as angina or a heart attack, where blood flow to the heart muscle is restricted. Sensory nerve fibers from the heart enter the spinal cord at the same thoracic levels (T1–T5) as the nerves supplying the left arm and shoulder. This shared neural pathway means cardiac pain can present as a crushing sensation in the chest that radiates down the left arm, shoulder, or jaw. Sometimes, it appears in the shoulder without significant chest discomfort.
Irritation of the diaphragm, the muscular wall separating the chest and abdomen, can also cause referred pain to the shoulder. Conditions affecting nearby organs, such as the spleen or pancreas, can stimulate the phrenic nerve. This nerve shares roots (C3–C5) with the sensory nerves of the shoulder region. Abdominal problems like a ruptured spleen or a subphrenic abscess can sometimes manifest as discomfort in the left shoulder.
Pain Originating from the Neck and Nerves
Pain originating in the neck but felt in the shoulder is known as cervical radiculopathy, resulting from the irritation or compression of a nerve root in the cervical spine. Common causes include a herniated disc or degenerative changes like bone spurs (osteophytes) that narrow the nerve exit space. The C5 nerve root is particularly relevant, as it supplies sensation and motor function to the shoulder and upper arm muscles.
This neurogenic pain differs from localized muscle or joint pain. Patients often describe the discomfort as sharp, burning, or electric-like, radiating from the neck or shoulder blade down the arm. The pain is accompanied by neurological symptoms such as tingling (paresthesia) or numbness in a specific pattern down the limb, corresponding to the affected nerve’s dermatome.
Cervical radiculopathy can also cause muscle weakness in the shoulder or arm because the compressed nerve cannot properly transmit motor signals. Neck movements, such as extending the head backward or turning it to the side, typically worsen the shoulder pain. These actions temporarily increase pressure on the irritated nerve root. The precise location of the pain, such as the upper shoulder for C5 involvement or the outer shoulder for C6, helps clinicians distinguish this source from a localized shoulder injury.
Immediate Care and Medical Alert
For many instances of left shoulder discomfort, initial management involves basic self-care to reduce inflammation and protect the joint from further strain. Applying ice to the affected area for 15 to 20 minutes several times a day helps reduce acute swelling and pain, especially after an injury. Temporary rest from aggravating activities, combined with over-the-counter non-steroidal anti-inflammatory drugs, can often resolve symptoms related to mild tendinitis or muscle strain.
Certain signs indicate the need for immediate professional medical attention, suggesting a serious underlying cause like a heart attack. Urgent care is required if the left shoulder pain is sudden and severe, or if it is accompanied by symptoms such as:
- Crushing chest pressure
- Shortness of breath
- Lightheadedness
- Cold sweats
These symptoms should prompt an emergency call immediately.
If the pain is persistent, interferes with sleep, or limits daily function for more than a few days, a medical evaluation is warranted. If the pain travels down the arm and is associated with significant weakness, numbness, or a pins-and-needles sensation, it suggests nerve involvement that requires assessment. Seeking diagnosis for these persistent symptoms ensures the underlying condition can be addressed before it leads to long-term functional impairment.