What is Dystonia?
Dystonia  is a movement disorder that causes the muscles to contract and spasm  involuntarily. The neurological mechanism that makes muscles relax when  they are not in use does not function properly. Opposing muscles often  contract simultaneously as if they are 'competing' for control of a body  part. The involuntary muscle contractions force the body into  repetitive and often twisting movements as well as awkward, irregular  postures. There are approximately 13 forms of dystonia, and dozens of  diseases and conditions include dystonia as a major symptom.
Dystonia may affect a single body area or be 
generalized  throughout multiple muscle groups. Dystonia affects men, women, and  children of all ages and backgrounds. Estimates suggest that no less  than 300,000 people in North America are affected. Dystonia causes  varying degrees of disability and pain, from mild to severe. There is  presently no cure, but multiple treatment options exist and scientists  around the world are actively pursuing research toward new therapies.
Although  there are multiple forms of dystonia and the symptoms of these forms  may outwardly appear quite different, the element that all forms share  is the repetitive, patterned, and often twisting involuntary muscle  contractions.
Dystonia is a chronic disorder, but the vast  majority of dystonias do not impact cognition, intelligence, or shorten a  person's life span. The main exception to this is dystonia that occurs  as symptom of another disease or condition that can cause such  complications.
Information supplied by http://www.dystonia-foundation.org/pages/what_is_dystonia_/26.php