Stroke or Transient Ischemic Attack (TIA): The most common cause of sudden onset hand weakness, especially if accompanied by other symptoms like facial weakness, speech difficulties, or numbness.

Radial Neuropathy: Compression or injury to the radial nerve can cause weakness or paralysis of the muscles it supplies, leading to hand weakness.
Cervical Spondylosis or Herniated Disc: Compression of the spinal nerves in the cervical spine can cause hand weakness, numbness, or tingling.
Peripheral Neuropathy: Conditions like diabetes, vitamin deficiencies, or autoimmune disorders can cause peripheral neuropathy, leading to hand weakness.
Musculoskeletal Injuries: Trauma or overuse injuries to the hand, wrist, or forearm can cause weakness or pain in the hand.

Spinal Cord Compression: Compression of the spinal cord can cause rapid progression of symptoms, including hand weakness, and requires urgent medical attention.
Multiple Sclerosis: An autoimmune disease that can cause a wide range of neurological symptoms, including hand weakness, and requires prompt diagnosis and treatment.
Tumors (Brain or Spinal): Although rare, tumors can cause hand weakness and other neurological symptoms, and early detection is crucial for treatment.
Infections (e.g., Abscess, Meningitis): Infections like abscesses or meningitis can cause hand weakness, among other symptoms, and require immediate medical attention.

Amyotrophic Lateral Sclerosis (ALS): A progressive neurological disease that affects motor neurons, causing hand weakness, among other symptoms.
Guillain-Barré Syndrome: A rare autoimmune disorder that can cause rapid onset of hand weakness, among other symptoms.
Charcot-Marie-Tooth Disease: A group of inherited disorders that affect the peripheral nerves, causing hand weakness, among other symptoms.
Plexopathies: Injuries or conditions affecting the brachial plexus, a network of nerves that supplies the arm and hand, can cause hand weakness.