Cervical Radiculopathy: This condition, often resulting from a herniated disk or bone spur in the cervical spine, can compress or irritate nerves, leading to pain in the upper back and tingling sensations in specific fingers, depending on which nerve root is affected. The left index finger is typically innervated by the C7 nerve root, making C7 radiculopathy a likely cause.

Thoracic Outlet Syndrome (TOS): This condition involves 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. It can cause pain in the shoulders and upper back and tingling in the fingers.
Carpal Tunnel Syndrome: Although more commonly associated with median nerve compression at the wrist, carpal tunnel syndrome can cause tingling in the index finger. However, it typically also involves the thumb, middle finger, and half of the ring finger.
Ulnar Nerve Entrapment: This condition can cause tingling but is more commonly associated with the little and ring fingers. However, in some cases, it might radiate to other areas, including the index finger, especially if there's a more proximal entrapment.

Spinal Cord Compression: Conditions like spinal stenosis, tumors, or abscesses can compress the spinal cord, leading to severe neurological deficits. Early recognition and treatment are crucial to prevent permanent damage.
Myelopathy: This refers to any neurological deficit resulting from compression or injury of the spinal cord. It can present with a variety of symptoms, including pain, numbness, tingling, and weakness, and requires prompt medical attention.
Acute Coronary Syndrome: Although less directly related to the symptoms described, new-onset upper back pain, especially if radiating to the arm, can be a presentation of cardiac ischemia, particularly in women. It's essential to consider cardiac causes, especially in patients with risk factors.

Pancoast Tumor: A type of lung cancer located at the top of the lung that can invade the brachial plexus, causing arm pain and tingling.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of neurological symptoms, including numbness, tingling, and pain.
Syringomyelia: A disorder in which a fluid-filled cavity or syrinx forms within the spinal cord, leading to neurological symptoms, including pain, numbness, and tingling.