Pathophysiology of Sialorrhea

Stuart Isaacson, MD: Do you distinguish, when you think about sialorrhea, between which glands produce saliva, whether it’s during the resting state or when they’re eating? Because we have the parotid glands, the submandibular, the sublingual glands. How do you think about that? Does that come into the clinical picture?

Richard M. Trosch, MD: It does. Obviously, our parotid is the largest gland we have. We’ll talk a little later about botulinum toxic injections for this. It’s a big target, and it’s fairly consistent in different people versus submandibular glands right under here, usually in the posterior third, just on the inner table of the mandible. It’s a much smaller gland and different type of saliva. Then we do have the sublingual. So we have these 6 pairs and these hundreds of minor salivary glands.

The parotid produces a more serious type of saliva that is more protein rich, because that is where amylase is coming from.

The sublingual is all mucin—so mucus is coming from there. And the submandibular is really a combination of both, some serous and some mucin production as well. The saliva we produce when we’re eating—so in response to a meal—that’s stimulated state, that’s all coming from our parotid. Most of the unstimulated state is coming actually from our submandibular. So it is important in terms of size. The submandibulars are variable in their size. It can vary almost 10-fold and in their location. The parotid is more consistent in size and location, so it does make an easier target.

Stuart Isaacson, MD: These salivary glands are under the control of the autonomic nervous system.

Richard M. Trosch, MD: Correct.

Stuart Isaacson, MD: It’s the sympathetic and parasympathetic innervation that lead to the release of acetylcholine, which causes these cells to produce saliva.

Richard M. Trosch, MD: Right. The parasympathetic is really what drives the production of the saliva and tells the glands to secrete saliva. The sympathetic is important for telling the ducts to relax and allow the flow of saliva. I think of it more of a parasympathetic and muscarinic type of receptor that we want to hit.

Stuart Isaacson, MD: So it’s a different acetylcholine receptor in the glands. It’s the muscarinic one.

Richard M. Trosch, MD: Yes.

Stuart Isaacson, MD: Not what we think about in muscles.

Richard M. Trosch, MD: Muscles for other botulinum toxic injections.

Stuart Isaacson, MD: We think about Parkinson disease as being a widespread supranuclear degeneration, and it involves the enteric nervous system, and we know it involves the autonomic nervous system. We’ve almost overlooked the idea that the autonomic nervous system in Parkinson is responsible not only for problems with bladder and blood pressure but really for saliva production.

Richard M. Trosch, MD: Right. But in this case, it actually is reducing it.

Stuart Isaacson, MD: It’s reducing it, right.

Richard M. Trosch, MD: Which is beneficial. It’s just not reducing it enough because they’re swallowing; they still can’t keep up with this reduced flow.