Dry mouth can also be a sign of underlying disease

Sicca syndrome or sicca symptoms are often listed as additional features in ME/CFS or FM—the term "sicca" refers to dryness of the eyes and mouth (i.e., it describes a symptom). When problems with dryness become chronic and are accompanied by other symptoms or new problems, including noticeable changes in dental/oral health, patients should be professionally evaluated to determine its cause.

The reason to do so is because dry mouth can be a sign of many underlying diseases such as certain types of diabetes or central nervous system diseases, infections, amyloidosis, sarcoidosis, and autoimmune disorders.

For example, dry mouth and dry eyes are the hallmark symptoms of Sjögren's Syndrome (SS) and dryness, in this case, is usually the result of disruption or malfunction of exocrine gland secretion. It can affect other organs and lead to serious problems without medical intervention and follow-up.

SS may be accompanied by other illnesses (i.e., connective tissue diseases, certain thyroid problems, celiac disease, and other autoimmune disorders), including FM. Although FM is not an autoimmune illness, about half of the patients with SS will report symptoms of FM (i.e., as exacerbation of pain, fatigue and cognitive dysfunction).

A comorbidity between FM and SS has been established (i.e., several studies show it may affect 47 to 55 percent of patients); therefore, it is not unreasonable that patients who develop new symptoms or worsening of existing symptoms get worked up for other potential conditions (i.e., doctors should not attribute everything to FM nor any other existing primary diagnosis).

[Comment: Even though ME/CFS is not mentioned as one of the diseases or conditions associated with SS in the book used for this article, leading researchers/clinicians have found SS in a subset of ME/CFS patients. The same advice would apply to patients with ME/CFS.]