Carpal Tunnel Syndrome: This condition is the most common cause of numbness in the hand, particularly affecting the thumb, index, middle finger, and part of the ring finger. It occurs due to compression of the median nerve as it passes through the wrist.

Ulnar Nerve Entrapment: This condition affects the little finger and ring finger, causing numbness, tingling, and weakness. It can occur at the elbow or wrist due to compression of the ulnar nerve.
Radial Nerve Compression: Although less common, compression of the radial nerve can cause numbness on the back of the hand or the thumb side of the hand.
Thoracic Outlet Syndrome: This condition involves compression of the nerves and/or blood vessels that pass into the thoracic outlet (the space between your collarbone and first rib), leading to numbness in the hand, among other symptoms.
Herniated Cervical Disk: A herniated disk in the cervical spine can compress nerves that travel to the hand, leading to numbness, particularly if the disk affects the C6 or C7 nerve roots.

Stroke or Transient Ischemic Attack (TIA): Although less common as a cause of isolated hand numbness, a stroke or TIA can present with sudden onset of numbness, and missing this diagnosis can be catastrophic.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of neurological symptoms, including numbness. Early diagnosis is crucial for management.
Spinal Cord Injury or Compression: Any condition that compresses or injures the spinal cord can lead to numbness, among other neurological deficits.

Vitamin B12 Deficiency: Can cause neurological symptoms including numbness or tingling in the hands and feet.
Peripheral Neuropathy: Conditions such as diabetes, certain infections, or exposure to toxins can cause peripheral neuropathy, leading to numbness in the hands.
Tumors: Rarely, tumors affecting the nerves (e.g., schwannomas) or the spinal cord can cause numbness in the hand.
Syringomyelia: A condition characterized by the formation of a fluid-filled cavity or syrinx within the spinal cord, which can expand and compress the spinal cord from inside, leading to numbness and other neurological symptoms.