Cervical Radiculopathy: This condition, often resulting from a herniated disk or bone spur in the cervical spine, can compress or irritate nerves, leading to numbness in the arm. The distribution of numbness can vary depending on which nerve root is affected, making it a common cause of arm numbness.

Thoracic Outlet Syndrome: Compression of the nerves and/or blood vessels that pass into the thoracic outlet (the space between your collarbone and first rib) can cause numbness in the arm, among other symptoms.
Peripheral Neuropathy: Conditions such as diabetes, vitamin deficiencies, or alcohol abuse can lead to peripheral neuropathy, which may cause numbness in the limbs, including the right arm.
Brachial Plexus Injury: Trauma to the brachial plexus, a network of nerves that conducts signals from the spinal cord to the shoulder, arm, and hand, can result in numbness, weakness, or paralysis of the arm.

Stroke or Transient Ischemic Attack (TIA): Although less common as a cause of isolated arm numbness, a stroke or TIA can present with sudden onset of numbness in one arm and is a medical emergency. Early recognition and treatment are crucial to prevent long-term damage.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of neurological symptoms, including numbness. It's essential to consider this diagnosis to initiate appropriate treatment and management.
Spinal Cord Injury or Compression: Conditions such as spinal stenosis, tumors, or abscesses can compress the spinal cord, leading to numbness, weakness, or paralysis. Prompt diagnosis and treatment are necessary to prevent permanent damage.

Vitamin B12 Deficiency: A deficiency in vitamin B12 can lead to neurological symptoms, including numbness or tingling in the hands and feet, though it's less commonly associated with unilateral arm numbness.
Lyme Disease: In its later stages, Lyme disease can cause neurological problems, including numbness or weakness in the limbs, though this is relatively rare.
Sarcoidosis: A condition that can lead to inflammation in various parts of the body, including the nervous system, causing numbness or weakness, among other symptoms. Neurosarcoidosis is rare but can have significant implications if not treated.