Transient Ischemic Attack (TIA): A brief episode of numbness in one extremity can be a classic presentation of a TIA, often referred to as a "mini-stroke." This condition is caused by a temporary decrease in blood supply to part of the brain, which can result from a variety of factors including emboli, thrombosis, or vasospasm.

Migraine: Some individuals experience neurological symptoms, including numbness or tingling in an extremity, as part of a migraine aura. These symptoms are usually transient and can be accompanied by other migraine features such as headache, visual disturbances, or sensitivity to light and sound.
Radial Neuropathy or Other Focal Neuropathies: Compression or injury to the nerves supplying the arm can cause numbness. This could be due to various reasons such as sleeping position, direct trauma, or compression by anatomical structures.
Cervical Spondylosis or Disc Disease: Compression of the spinal nerves in the neck can lead to numbness in the arm. This condition is more common in older adults and can be associated with neck pain and stiffness.

Stroke: Although similar to TIA, a stroke is characterized by persistent neurological deficits. Early recognition and treatment of stroke are crucial to minimize brain damage and improve outcomes.
Multiple Sclerosis: This autoimmune disease can cause a wide range of neurological symptoms, including numbness in an extremity. It's essential to consider MS, especially in younger patients with recurrent or multifocal neurological symptoms.
Subclavian Steal Syndrome: A rare condition where there is a significant stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery, leading to reversal of blood flow in the vertebral artery. This can cause symptoms similar to TIA, including arm numbness.

Hyperventilation Syndrome: Can cause tingling or numbness in the extremities due to respiratory alkalosis, which affects nerve function.
Peripheral Artery Disease (PAD): Although more commonly associated with leg symptoms, PAD can rarely cause arm symptoms, including numbness, especially during exercise.
Neurodegenerative Diseases (e.g., Amyotrophic Lateral Sclerosis): These conditions can cause a variety of neurological symptoms, including numbness, but are less likely to present with transient, unilateral upper extremity numbness as an isolated symptom.