78 CHAPTER 3 after BoNT-A treatment since children in the study by van Hulst et al.6 received submandibular BoNT-A injections for the first time whereas children in our study received a mean of 2.3 BoNT-A injections before bilateral submandibular duct ligation. Adverse events after bilateral submandibular duct ligation occurred in four children (13.8%); this broadly corresponds to the 19% adverse events reported by Scheffer et al.14 A strength of the current study is the within-participant comparison of two management strategies to treat drooling. Childrenwith CP and neurodevelopmental disabilities form a heterogeneous population where there is much variability, not solely in the physical and mental expression of the condition, but also in response to treatment since response to BoNT-A treatment varies with each individual. The chosen observational design enables within-participant comparison of both BoNT-A injection and bilateral submandibular duct ligation; therefore, it reduces the influence of covariates and strengthens study reliability. However, this study also has several limitations. There is a strong potential for selection bias since one of the main reasons to terminate BoNT-A injections is an inadequate effect, which is reflected by the relatively high subjective VAS scores compared to the objective drooling quotient scores.25 It could be argued that only poor responders to BoNT-A treatment were included in this study. However, although VAS scores at 32 weeks were significantly higher in this study compared to the larger cohort of patients undergoing BoNT-A (n=232), there was a significant decrease in the objective outcome (drooling quotient) after 32 weeks, which is equal to that recorded for the larger cohort of patients treated with BoNT-A. This suggests that there was an adequate objective reduction in drooling without an equal subjective reduction, thereby making it unlikely that only poor responders to a reduction in drooling were included. The VAS may be influenced by dissatisfaction caused by former experiences with BoNT-A treatment, any benefits not outweighing the related burden of the BoNT-A procedure, or any results not meeting preset expectations. Additionally, wishing for a permanent solution might consciously or unconsciously lead to a higher VAS score. Another concern in this
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