Factors Influencing Response to One BoNT-A Injection Cycle in Subjects Suffering From Idiopathic Cervical Dystonia

To describe TWSTRS change scores from inclusion (total score & subscales scores)

Time frame: Baseline, and around 4 weeks and 3 months post injection

To describe tremor change score from inclusion (TSUI scale)

Time frame: Baseline, and around 4 weeks and 3 months post injection

To describe the Cervical Dystonia Impact Profile (CDIP) 58 change from inclusion

Time frame: Baseline, and around 4 weeks post injection

To describe subject and investigator's CGI scores

Time frame: Around 4 weeks post injection

To identify prognostic factors for response (Exploratory Objective)

Time frame: baseline, and around 4 weeks and 3 months post injection