Role of thyroid hormones in burning mouth syndrome. Systematic review.

Background: Burning mouth syndrome is an idiopathic condition characterized by burning pain in a normal-appearing oral mucosa lasting at least four to six months. In the case of secondary burning mouth syndrome is associated with local or systemic factors (such as thyroid disorders) that can cause these symptoms. The aim of this review was to study the relationship between thyroid disorders and burning mouth syndrome.

Material and methods: The present study followed the PRISMA guidelines. An electronic search strategy was developed for PubMed/Medline, Scopus and Cochrane. The following combination of keywords and Boolean operators were used: Thyroid AND burning mouth; Thyroid AND burning mouth syndrome; Hypothyroidism AND burning mouth; Hypothyroidism AND burning mouth syndrome; Hyperthyroidism AND burning mouth; Hyperthyroidism AND burning mouth syndrome. The results were processed by existing free software in https://www.graphpad.com/. To evaluate the association of the categorical variables we used the Fisher test at a level of significance of p-value ≤ 0,05. As a primary summary measure the Odds Ratio (OR) has been used. To analyze the risk of bias the guidelines of the GRADE guide were used and the grade of evidence was analyzed by the guide of Joanna Briggs Institute: Levels of Evidence and Grades of Recommendations.

Results: After applying the inclusion and exclusion criteria, 5 studies were selected for review. The Chi-square was 10.92 and the Odds Ratio was 3.31 with respect to TSH values with p <0.0001 (Fisher's test). The population of patients with TSH alterations is increased in 80.49% and decreased in 19.51%.

Conclusions: It can be concluded that thyroid hormone abnormalities are a factor in secondary burning mouth syndrome; specially in patients with hypothyroidism.