Botulinum neurotoxin type A (BoNT/A) is first-line treatment in patients suffering from cervical dystonia. Effect of BoNT/A is temporary and must be repeated to maintain clinical effect. As for all biologics, repeated treatment bears the risk of activating an immune response due to the immunogenic nature of foreign proteins. Clinical signs of a potential immune response are reduced, or loss of efficacy, decreased duration of effect, and the need of a dose increase to maintain effect. Due to the different degree of purity and protein content, it is reasonable to assume that commercial BoNT/A formulations differ in immunogenic properties.~Pivotal clinical trials and monocentric real-world studies demonstrated an increased incidence of neutralizing antibodies (NAbs) and NAb-associated partial or complete secondary non-response. However, the clinical relevance of potential immunogenicity-related mechanisms has not been demonstrated in a larger multicentric cohort in a real-world setting. This chart abstraction is designed to address this gap.
The goal of this retrospective, international, multi-center chart abstraction is to learn about the long-term impact of product-specific immunogenicity-related factors in different botulinum neurotoxin type A formulations in patients suffering from cervical dystonia. The main question it aims to answer is:~Do complex-containing (CC) botulinum toxin formulations impact the long-term clinical outcome in cervical dystonia patients compared to a complex-free (CF) formulation?~Researchers will compare differences observed in years 2 and 7 between two toxin groups, i.e., botulinum neurotoxins type A containing complexing proteins (CC) and without complexing proteins (CF).