68 CHAPTER 3 METHODS Study design We retrospectively identified children who had first been treated with bilateral submandibular BoNT-A injections and who subsequently underwent bilateral submandibular duct ligation surgery. The study design, which reflects clinical practice, compared the effect of bilateral submandibular duct ligation to BoNT-A treatment in each participant, thus reducing confounding factors and increasing reliability and statistical power in a heterogeneous population of children with CP and other non-progressive developmental disorders. Regarding multiple BoNT-A procedures preceding bilateral submandibular duct ligation, only data from the latest BoNT-A injection was used for analysis. Original standardized assessments were made by a specialized speech and language therapist before each treatment and again at 8 and 32 weeks after treatment. Participants All children eligible for participation visited the Multidisciplinary Saliva Control Center of the Radboud University Medical Center, Nijmegen, the Netherlands, between December 2005 and October 2017. The cohort was evaluated retrospectively. Participants diagnosed with CP or a non-progressive developmental disorder accompanied by severe drooling, who chose to discontinue repeated BoNT-A injections, were included. Reasons given for surgery preference included experiencing inadequate drooling control, BoNT-A side effects, or the desire for a long-term solution. Exclusion criteria included: concurrent alternative treatment for drooling; fewer than 6 months or more than 5 years between the last BoNT-A injection and bilateral submandibular duct ligation; more than one missing followup measurement; or a missing baseline measurement (Table 1). The research was performed in accordance with national and international ethical standards. The regional review board decided that specific ethical permission for this observational study was not required. Informed consent by caregivers was provided before each intervention.
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