Consists of sustained or repetitive involuntary muscle contractions, frequently causing twisting movements and abnormal posture. May be generalized or focal; >300,000 cases in the United States.

Focal dystonias are common and include blepharospasm of the eyelids; spasmodic dysphonia involving the vocal cords; oromandibular dystonia of the face, lips, tongue, and jaw; cervical dystonia of the neck musculature (torticollis); and limb dystonias that are often task specific such as writer's cramp, playing a musical instrument (musician's cramp), or putting in golf (yips).

More than 16 causative genes have been identified. Idiopathic torsional dystonia is a predominantly childhood-onset form of generalized dystonia with an autosomal dominant pattern of inheritance that mainly affects Ashkenazi Jewish families; most are linked to a mutation in the DYT1 gene on chromosome 9. Other generalized dystonias occur as a consequence of drugs such as antiemetics, neuroleptics, and treatments for Parkinson's disease.

• Therapy for focal dystonias usually involves botulinum toxin injections into the affected musculature.
• All forms of dystonia may respond to anticholinergic medications (e.g., trihexyphenidyl 20-120 mg/d), baclofen (20-120 mg/d), or tetrabenazine (initial dose 12.5 mg/d, usual maintenance 25-75 mg/d).
• Surgical therapies, including deep brain stimulation (DBS), may be effective in refractory cases.