This study shows that BTX injection into salivary glands can decrease saliva production, reducing excessive drooling in a small sample of patients affected by RS. Improvement in hypersalivation seems also to affect positively a few RS clinical features related to oral motor dysfunctions.
Previous studies showed that BTX-A is effective in reducing drooling both in adults with neurodegenerative disorders and in children with CP [10]. This is the first report of BTX treatment for sialorrhea in children and young adults affected by a genetic disorder like RS. All patients were injected with the same brand of BTX, incobotulinumtoxin A, in order to have more reliable results for comparisons among patients. Patients received the dose of 150 U that is higher in comparison to the amount reported in previous studies on the treatment of sialorrhea. When our study started, there was no official indication of BTX for excessive salivation and we chose to give that dose because, in our experience, it was effective and safe if injections were performed under ultrasound guidance.
Considering the similarities of commercially available toxins, it is reasonable that both abobotulinum and onabotulinum toxin A would provide analogous results [11].
Injections were performed under ultrasound guidance to localize precisely BTX spreading into salivary glands and to prevent diffusion on contiguous muscles that may produce further swallowing difficulties. Just in one case dysphagia became more severe for a few weeks after the treatment with no other complications. The remaining four patients did not report any adverse event following BTX injections.
In order to assess a possible effect of BTX treatment for sialorrhea on other clinical features, oral motor and upper respiratory functions were investigated using three selected items of RARS [8, 9]. Eating habits and bruxism significantly improved in the weeks following treatment with BTX and worsened again when the toxin effect was wearing off. Therefore, saliva reduction may also give benefits on different clinical aspects. Eating could become indeed easier for patients having less retention of saliva. Interestingly, bruxism also improved after drooling reduction. We could speculate that an excessive amount of saliva may enhance jaw-closing movements; therefore, a decrease in salivation may improve bruxism. However, a masticatory muscle relaxation due to BTX spreading from parotid glands can not be excluded [12]. Unfortunately, our study did not show a correlation between drooling production and respiratory performances, although we found a slight tendency of dyspnoea improvement after BTX treatment.
Results of the present study are restricted just to the first treatment with incobotulinumtoxin A. Actually, BTX injections can be performed recurrently with efficacy and safely [13] in different neurological disorders and it is reasonable that patients with RS can be treated regularly in case of excessive drooling.
Hypersalivation in RS is likely related to severe swallowing difficulties and contributes to complication of oral motor functions. This study is limited by the small number of patients, but our results would suggest that BTX injection in salivary glands is safe and effective in reducing saliva production in RS. Moreover, patients would also benefit from the treatment for more oral motor problems possibly related to hypersalivation like eating difficulties and bruxism. More extensive studies are needed to confirm these data. In conclusion, BTX treatment for sialorrhea in patients with RS should be encouraged because it is effective and safe and it may also improve important oral motor functions.