• Dysport
• Botox
• cervical dystonia
• swallowing

Defining a conversion ratio between Botox and Dysport mouse units to compare their therapeutic potencies has puzzled neurologists for years: initial studies used inadequate clinical models, such as blepharospasm, hemifacial spasm, or spasmodic dysphonia, which are extremely dose insensitive with respect to their therapeutic outcome and side effects. A later study used cervical dystonia as a more sensitive model, but referred to independent patient groups, thus provoking criticism because of vast interinvidual cervical dystonia differences. By using cervical dystonia and applying a crossover design, the study by Ranoux and colleagues¹ certainly has methodological advantages over previous ones. However, it has its own flaws: with durations of action in the Dysport 1:4 group ranging from 0 to 491 days and a substantially larger standard deviation in this than in any other group, the Dysport 1:4 group obviously contains at least one, if not more, patients with clearly abnormal and unusual responses, thus erroneously overestimating this group’s duration of action. The Dysport 1:3 group with a normal range of durations of action, was not significantly different from the Botox group. The meaning of a duration of action of 0 days in the Botox group and in the Dysport 1:3 group remains unclear. With the pain score in the Botox group being substantially lower …