I'm hoping someone can point me to a neurological condition that would cause a gradual motor deterioration (like Parkinson's perhaps), but which could be aggravated by an injury.
I have a character with a tremor who gets beaten up badly. I'd like for him to be hospitalized, and for it to become clear that he'll never improve. Any ideas?
I don't think I'm quite sure what you're asking for here. Do you want just the tremor to worsen? But the tremor is already going to be progressive, and you want it to suddenly worsen from an injury?
If a patient has a condition called cervical myelopathy, that means there is some sort of pressure on the spinal cord in the area of the neck - could be from arthritic changes, a congenitally tight space around the spinal cord, a herniated disk, a tumor, etc. This can cause progressive problems like weakness in the limbs, decreased coordination, balance problems, spasticity (abnormal increased muscle tone), difficulty walking or using the arms/hands, sensory changes, and bowel and bladder issues like incontinence. Sometimes (often) this comes on pretty gradually.
If this person has a sudden injury to the neck, (like whiplash from a car accident or fall), then that condition can suddenly worsen to any degree of severity, including permanent spinal cord injury and complete paralysis, depending on how bad the new insult is. Beating someone up can certainly be a way to worsen this condition. And you can have the severity and combination of symptoms pretty much how you want it to fit the story.