Cervical Radiculopathy: This condition, often resulting from a herniated disk or bone spur in the cervical spine, compresses or irritates the nerves that radiate to the shoulder and arm, causing pain. The symptoms can include pain, numbness, or weakness in the shoulder and arm, making it a common cause for the described symptomatology.

Subacromial Bursitis/Tendinitis: Inflammation of the bursa or tendons in the shoulder can cause pain that radiates down the arm, especially with movements of the shoulder.
Thoracic Outlet Syndrome: Compression of the nerves or blood vessels that pass into the thoracic outlet (the space between your collarbone and first rib) can cause pain in your shoulders and neck and numbness in your fingers.
Brachial Plexus Injury: Damage to the brachial plexus, the network of nerves that conducts signals from the spinal cord to the shoulder and arm, can cause pain, numbness, and weakness in the arm.

Myocardial Infarction (Heart Attack): Although less common, pain from a heart attack can radiate to the arm, and it is crucial to rule out cardiac causes, especially in patients with risk factors for coronary artery disease.
Pulmonary Embolism: In rare cases, a pulmonary embolism can cause referred pain to the shoulder and arm, particularly if the embolism involves the upper parts of the lung.
Aortic Dissection: A tear in the aorta's inner layer can cause severe, tearing pain that can radiate to the arm, among other areas.

Pancoast Tumor: A type of lung cancer located at the top of the lung that can invade the brachial plexus, causing shoulder and arm pain.
Referred Pain from Abdominal Pathologies: Certain abdominal conditions, such as gallbladder disease or pancreatitis, can cause referred pain to the shoulder and arm due to shared nerve roots.
Complex Regional Pain Syndrome (CRPS): A chronic pain condition characterized by severe, burning pain at the site of an injury, which can sometimes be referred to the arm from the shoulder.