Cervical Spondylosis: This condition, which involves wear and tear on the discs in the neck, is a common cause of numbness and weakness in the arms due to compression of the spinal nerves. It is prevalent in the aging population and can be exacerbated by activities that involve repetitive neck motion.

Carpal Tunnel Syndrome: A condition that occurs when the median nerve, which runs from the forearm into the palm of the hand, becomes pressed or squeezed at the wrist. Symptoms include numbness, tingling, and weakness in the hand and arm.
Thoracic Outlet Syndrome: 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. This can lead to pain in your shoulders and neck and numbness in your fingers.
Radial Neuropathy: Also known as radial nerve palsy, this condition can cause numbness, weakness, or a tingling sensation in the back of the hand or the fingers, especially the back of the thumb and the area around it.

Stroke or Transient Ischemic Attack (TIA): Although less common as a cause for isolated arm numbness or weakness, a stroke or TIA can present with sudden onset of these symptoms. Missing this diagnosis can be catastrophic, making it crucial to consider, especially in patients with risk factors for cerebrovascular disease.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of potential neurological symptoms, including numbness, weakness, vision loss, and tremor. Early diagnosis is critical for management.
Spinal Cord Injury or Compression: Conditions such as spinal stenosis, herniated discs, or tumors can compress the spinal cord, leading to numbness, weakness, and potentially more severe neurological deficits.

Guillain-Barré Syndrome: A rare neurological disorder in which the body's immune system mistakenly attacks part of its peripheral nervous system, leading to muscle weakness, and sometimes paralysis, among other symptoms.
Lyme Disease: Caused by the bacterium Borrelia burgdorferi, transmitted to humans through the bite of infected black-legged ticks. Neurological symptoms can include numbness, weakness, and Bell's palsy.
Vitamin Deficiencies (e.g., Vitamin B12 Deficiency): Can lead to neurological symptoms including numbness or tingling in the hands and feet, though arm weakness is less common.