Stroke: The most common cause of sudden onset severe motor deficit, stroke can result in a range of symptoms from mild to severe, depending on the area and amount of brain tissue affected.

Spinal Cord Injury: Trauma to the spinal cord can cause immediate and severe motor deficits, depending on the level and severity of the injury.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of neurological symptoms, including progressive motor deficits.
Amyotrophic Lateral Sclerosis (ALS): A progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord, causing loss of muscle control.
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.

Spinal Cord Compression: Can be caused by trauma, tumors, or other conditions, leading to severe and progressive motor deficits if not promptly treated.
Meningitis or Encephalitis: Infections that inflame the meninges or brain tissue, respectively, and can cause severe neurological symptoms, including motor deficits.
Cauda Equina Syndrome: A condition that occurs when the nerves in the spinal canal are compressed, leading to severe and potentially permanent neurological damage if not promptly treated.

Krabbe Disease: A rare genetic disorder that affects the nervous system, leading to severe and progressive neurological symptoms, including motor deficits.
Tay-Sachs Disease: A rare genetic disorder that destroys nerve cells in the brain and spinal cord, leading to progressive neurological deterioration.
Adrenoleukodystrophy: A rare genetic disorder that affects the brain and spinal cord, leading to progressive neurological symptoms, including motor deficits.
Prion Diseases (e.g., Creutzfeldt-Jakob Disease): Rare, degenerative, and fatal brain disorders that can cause a range of neurological symptoms, including motor deficits.