Thoracic Outlet Syndrome (TOS): This is the most likely diagnosis given the symptoms, as TOS is characterized by compression, injury, or irritation of the nerves and/or blood vessels (arteries and veins) in the thoracic outlet area, which lies between your collarbone (clavicle) and first rib. This can lead to pain in your shoulders and neck and numbness in your fingers.

Cervical Spondylosis: This condition involves wear and tear on the disks in the neck (cervical spine), which can cause pain and numbness in the neck and arms, similar to TOS.
Rotator Cuff Tendinitis: Inflammation of the tendons of the rotator cuff muscles can cause pain and weakness in the shoulder, which might be confused with TOS symptoms.
Cubital Tunnel Syndrome: Compression of the ulnar nerve at the elbow can cause numbness and tingling in the ring and small fingers, similar to the nerve compression symptoms seen in TOS.

Pulmonary Embolism: Although less likely, a pulmonary embolism (a blood clot in the lungs) can present with sudden onset of chest pain and shortness of breath, which could be mistaken for TOS symptoms. Missing this diagnosis could be fatal.
Aortic Dissection: A tear in the aorta's inner layer can cause severe, sudden chest pain and could be confused with the chest pain associated with TOS. This is a medical emergency.
Cervical Disc Herniation: A herniated disc in the neck can compress nerves, causing pain, numbness, and weakness in the neck and arms. While not immediately life-threatening, it requires prompt treatment to prevent permanent nerve damage.

Pancoast Tumor: A rare type of lung cancer that grows in the upper part of the lung and can invade nearby tissues, including nerves, ribs, and vertebrae, causing shoulder and arm pain, as well as numbness.
Brachial Plexitis (Neuralgic Amyotrophy): An inflammatory condition that affects the nerves of the brachial plexus, causing severe pain, followed by weakness and atrophy of the muscles of the shoulder and arm.
Arterial Thoracic Outlet Syndrome: A rare form of TOS where the subclavian artery is compressed, potentially leading to arm pain, coolness, and weakness due to diminished blood flow.