Clinical Study of Ingrezza (Valbenazine) for the Treatment of Cervical Dystonia

Inclusion Criteria: * Male or female patients between 18 and 85 years of age (inclusive) * A clinical diagnosis of cervical dystonia (ie, spasmodic torticollis) by investigator for at least six months * Moderate to severe head tremor and/or dystonic posturing as judged by the investigator * Stable Botulinum Toxin (Botox, Dysport, Xeomin, or Myobloc) therapy dosage for at least 3 months prior to baseline visit Exclusion Criteria * Tardive dyskinesia * Predominant anterocollis * Concomitant use of strong CYP3A4 inhibitors (i.e. itraconazole, ketoconazole, clarithromycin), digoxin, strong CYP2D6 inhibitors (i.e. paroxetine, fluoxetine, quinidine), monoamine oxidase inhibitors (i.e. isocarboxazid, phenelzine, selegiline) * Myotomy or denervation surgery in the affected muscles (eg, peripheral denervation and/or spinal cord stimulation) * Diagnosis of Myasthenia gravis, Lambert-Eaton syndrome, amyotrophic lateral sclerosis, or any other significant neuromuscular disease which might interfere with the trial * Moderate to severe hepatic impartment as determined by a Child-Hugh Score ≥7 * Marked limitation on passive range of motion that suggests contractures or other structural abnormality, eg, cervical contractures or cervical spine syndrome * Any conditions that may increase the risk associated with study participation or may interfere with the interpretation of study results and, in the judgment of the Investigator, would make the patient inappropriate for entry into this study * Participation in another interventional study during participation in this study * Pregnant or lactating females, or females of child-bearing potential not willing to use an acceptable method of contraception * History of hypersensitivity to valbenazine or any components of INGREZZA. * Is suicidal at screening as defined by below: 1. According to the C-SSRS, he or she must not be actively suicidal at Visit 1 (Screening) or Visit 2 (Baseline) (including, an answer of "yes" to C-SSRS questions 4 or 5 \[current or over the last 6 months\]) and must not have attempted suicide in the 1 year prior to Visit 1 (Screening); OR 2. The subject is actively suicidal in the Investigator's judgment