According to the National Institute of Neurological Disorders and Stroke:
Dystonia is a movement disorder that causes involuntary contractions of your muscles. These contractions result in twisting and repetitive movements. Sometimes they are painful.
Dystonia can affect just one muscle, a group of muscles or all of your muscles. Symptoms can include tremors, voice problems or a dragging foot. Symptoms often start in childhood. They can also start in the late teens or early adulthood. Some cases worsen over time. Others are mild.
Some people inherit dystonia. Others have it because of another disease. Researchers think that dystonia may be due to a problem in the part of the brain that handles messages about muscle contractions. There is no cure. Doctors use medicines, Botox injections, surgery, physical therapy, and other treatments to reduce or eliminate muscle spasms and pain.
What this definition doesn’t tell you is that one can get dystonia due to brain trauma, including head injury and stroke. It also doesn’t tell you that currently no one is doing research on why people who have strokes or other brain trauma get dystonia. That’s because there are so few of us. Someday, I hope more research will be done for those of us who’ve had a stroke/brain trauma and developed dystonia as a result.