Cervical Radiculopathy: This condition, often due to a herniated disc or cervical spondylosis, can cause paresthesias in the upper extremity by compressing or irritating the nerve roots. The symptoms can vary depending on the specific nerve root involved but commonly include numbness, tingling, and pain in the arm.

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). It can cause paresthesias, pain, and weakness in the arm.
Carpal Tunnel Syndrome: Although more commonly associated with the median nerve, carpal tunnel syndrome can cause paresthesias in the hand, particularly in the thumb, index, middle finger, and half of the ring finger.
Ulnar Neuropathy: Compression of the ulnar nerve at the elbow or wrist can lead to paresthesias and weakness in the hand, particularly affecting the little and ring fingers.

Stroke or Transient Ischemic Attack (TIA): While less common, sudden onset of paresthesias in one arm can be a symptom of a stroke or TIA. Immediate medical attention is crucial.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of neurological symptoms, including paresthesias.
Spinal Cord Injury or Compression: Conditions such as spinal stenosis, tumors, or abscesses can compress the spinal cord, leading to paresthesias among other symptoms.

Vitamin Deficiencies (B12, B6): Deficiencies in these vitamins can lead to neurological symptoms, including paresthesias.
Peripheral Neuropathy: Caused by various factors including diabetes, alcohol abuse, or certain medications, leading to damage to the peripheral nerves and resulting in paresthesias.
Brachial Plexitis (Neuralgic Amyotrophy): An inflammatory condition affecting the brachial plexus, leading to severe pain and paresthesias in the arm.
Tumors: Rarely, tumors affecting the nerves or spinal cord can cause paresthesias in the upper extremity.