56 CHAPTER 2 submandibular duct ligation.12, 21 The decline in response after 2-DL is also unlike our experience with SMGE, where we saw a greater effect in both objective and subjective outcomes 32 weeks postoperatively.6 We cannot fully explain the difference in effect between SMGE and 2-DL; perhaps the formation of alternative salivary pathways contributes to renewed drooling after 2-DL.11, 14 Recurrence of drooling in themedium termafter 2-DL has been reported in previous studies. We found that 25.9% of the present population stopped responding in the period between 8 and 32 weeks follow-up, whereas recent studies reported 0% recurrence in 15 patients with 8 months follow-up14, and 7 out of 12 patients (58%) after a mean of 16 months follow-up using ligatures.11 This variation can perhaps be explained by a greater length of follow-up or the use of ligatures rather than vascular clips in the latter study. We feel ligatures might carry an increased risk for slippage, and increased tissue traction reaction, which would ultimately lead to alternative salivary pathway formation and thereby recurrence of drooling.13 Future studies should focus on the reason of recurrence, and what could be done to prevent it. Although the drooling severity (DS) did not diminish significantly following treatment, the drooling frequency (DF) was significantly reduced. One possible explanation for this difference is that the submandibular gland is responsible for two third of the total saliva in the unstimulated situation where the parotid gland is accountable for the majority of the total saliva in the stimulated situation.22 The result of treatment to the submandibular glands is mainly a relative reduction of the salivary flow in rest which leads to less frequent drooling throughout the day. However, the untreated parotid gland is the major source of saliva in stimulated situations. In these situations, it is therefore logical that the severity of drooling remains the same. Combined BoNT-A injections to both the submandibular and parotid glands could possibly match the effect of 2-duct ligation and internationally it is common to treat both the submandibular and the parotid gland at one time initially. In our institution, combined injections are only considered when there was no or insufficient response of submandibular botulinum toxin injections because
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