Saliva has several functions. It moisturizes the mouth cavity, lubricates the movement of food around the mouth and down the throat, and also contains enzymes that aid with digestion. We do not give saliva much thought unless there are problems like too much or too little of it. The latter can cause a host of symptoms beyond just a dry mouth. It can even affect taste, make chewing and swallowing difficult as well as increase the risk of mouth and dental infections.
What is hyposalivation?
Hyposalivation means that there is insufficient saliva or low saliva production. There are many reasons why hyposalivation may occur and it may be short lived (acute) or persist for long periods of time (chronic). The problem arises when the salivary glands do not produce or secrete sufficient saliva. However, the root cause may not always be with the salivary gland itself as its activity is influenced by a host of factors. The main symptom of hyposalivation is a dry mouth although it can have a host of other effects due to the function of saliva.
Saliva is produced by three paired salivary glands (sublingual, submandibular and parotid) as well as many tiny glands and mucus-producing cells lining the inside of the mouth. Collectively about 800mL to 2L of saliva is produced daily. A slight decrease in saliva volume is not usually a problem. However, once symptoms and complications of hyposalivation arise then treatment is required. Depending on the cause of hyposalivation, medication and sometimes even surgery is necessary.
Symptoms of Low Saliva Production
A dry mouth (xerostomia) is the most obvious symptom of hyposalivation. It is important to note that dry mouth is not always due to hyposalivation. Mouth breathing for example can lead to dryness of the mouth due to the airflow although the daily saliva production is within the normal range.
There are several other symptoms that may also be present with hyposalivation. Some may not be as obvious as the mouth dryness and only arise after a period of time. Other symptoms may be present immediately but are dependent on the degree of hyposalivation. The following symptoms may be present with hyposalivation as a direct result of the low saliva volume:
- Diminished taste
- Difficulty chewing and swallowing
- Speech disturbance, sometimes slurring or sensation of a thick tongue
- Tooth decay
- Increased risk of mouth infections
Many people mistaken a dry mouth for thirst and may drink large volumes of water. However, it is not increased thirst and the subsequent urinary symptoms, like frequent urination, is not due to any disease but just a consequence of the increased water consumption.
Causes of Hyposalivation
Dehydration is one of the more common causes of reduced saliva production. Since there fluid volume in the body is low, the body reduces the production of secretions like saliva. Dehydration can occur for various reasons. Most of the time it is due to fluid and electrolyte loss from vomiting and copious diarrhea as is seen with gastroenteritis. Excessive sweating with inadequate fluid replenishment is another cause as is blood loss. Sometimes dehydration arises with the use of certain drugs that promote fluid loss (diuretics).
Sjogren syndrome is one of the most common rheumatologic conditions that affects glands such as the salivary and tear glands. It arises when the immune system attacks these glands. As a result saliva production is reduced. Sjogren syndrome is a chronic disorder and the exact cause is unknown. However, as with many autoimmune disorders the cause is believed to be due to a prior viral or bacterial infection. Women, particularly those with a history of rheumatoid arthritis or SLE, are more likely to develop Sjogren syndrome.
Salivary gland infections are more likely to occur when there is some obstruction in the gland or duct which reduces saliva. Bacteria like Staphylococcus aureus are usually responsible for these infections. These infections are localized to the salivary gland and may infect surrounding tissue. Mumps is another cause as the salivary glands swell with this viral infection. However, the salivary glands may also be affected with systemic infections like in HIV.
Several drugs can cause salivary gland malfunction. Drugs like antidepressants, antihistamines, antipsychotics, sedatives, methyldopa, and diuretics are known to contribute to a low saliva volume. Sometimes these drugs do not directly affect saliva production but in the case of diuretics for example, the loss of fluid leads to a secondary reduction in saliva production. Chemotherapy can also affect the salivary glands and impair saliva production.
Stones can form in the salivary glands for various reasons. It is most commonly a result of precipitation of the components of saliva often related to dehydration. Chronic inflammation and sometimes impacted food debris may also give rise to the formation of salivary stones. It may remain asymptomatic until it becomes lodged in a duct leading out of the salivary gland. This is known as sialolithiasis and the stone may then obstruct the outflow of saliva.
Enlargement or swelling of the salivary glands may also be associated with decreased saliva production. There are many causes of salivary gland swelling including infections, diabetes, Sjogren syndrome, AIDS and tumors. The latter includes both benign (non-cancerous) and malignant (cancerous) tumors. It is not only the three large paired glands that are affected. Even the small glands may be affected by swelling like with trauma to the lip that causes the tiny lip glands to swell (mucocele).
Treatment of Low Saliva
The treatment for hyposalivation largely depends on the underlying cause. It is therefore important that the exact cause of the salivary gland malfunction is diagnosed. Treatment options may vary and can include dietary or lifestyle changes, medication and/or surgery. Salivary gland stones for example can sometimes be flushed out with drinking extra water and massaging the glands. Bacterial infections on the other hand often require antibiotics and tumors may require surgery for removal.
Certain drugs like pilocarpine and cevimeline can stimulate saliva production and secretion. However, these drugs will only work if the salivary gland is not damaged. Furthermore it will only provide symptomatic relief associated with hyposalivation and the root cause has to still be identified and treated.