How to manage a patient with burning mouth syndrome and hyperthyroidism?

Management of Burning Mouth Syndrome in Hyperthyroid Patients

Treat the hyperthyroidism first with antithyroid medication (methimazole 15-20 mg/day), as thyroid dysfunction is a recognized cause of secondary burning mouth syndrome, and correcting the thyroid abnormality may resolve the oral burning symptoms without additional interventions. 1, 2

Initial Assessment and Diagnostic Approach

Confirm Hyperthyroidism and Exclude Other Causes

• Measure TSH, free T4, and TSH-receptor antibodies to confirm hyperthyroidism and determine if Graves' disease is present 3
• Thyroid dysfunction is significantly associated with burning mouth symptoms, with an Odds Ratio of 3.31 (p<0.0001), making it a critical factor to address 2
• Hypothyroidism is more commonly associated with burning mouth syndrome than hyperthyroidism, but both thyroid disorders can cause oral burning 4, 2
• Perform thyroid ultrasound to evaluate for toxic adenoma or multinodular goiter, as this influences treatment choice between antithyroid drugs versus radioiodine 3

Distinguish Primary from Secondary Burning Mouth Syndrome

• Secondary burning mouth syndrome occurs when systemic factors like thyroid disorders cause the symptoms, and treating the underlying condition typically resolves the oral burning 4, 5
• Primary (idiopathic) burning mouth syndrome only applies after excluding all local, systemic, and psychological causes including thyroid dysfunction 5
• Do not diagnose primary burning mouth syndrome until thyroid function is normalized and symptoms persist for 4-6 months afterward 4, 2

Treatment Algorithm for Hyperthyroidism

First-Line Antithyroid Drug Therapy

• Start methimazole 15-20 mg/day as first-line treatment, as this dose minimizes the risk of agranulocytosis while effectively controlling hyperthyroidism 3
• Avoid propylthiouracil as first-line therapy due to risk of severe liver failure requiring transplantation or causing death 3
• Propylthiouracil should only be used during first trimester pregnancy or in patients with adverse reactions to methimazole 3
• Monitor for agranulocytosis risk, which is dose-dependent, by keeping methimazole dose ≤20 mg/day 3

Definitive Treatment Based on Etiology

• For toxic adenoma: proceed to radioiodine therapy after initial stabilization with antithyroid drugs 3
• Stop antithyroid drugs at least one week before radioiodine administration to reduce treatment failure risk 3
• For Graves' disease: if TSH-receptor antibodies remain >10 mU/L after 6 months of antithyroid treatment, remission is unlikely and radioiodine or thyroidectomy should be recommended 3
• If thyroidectomy is chosen, perform (near) total thyroidectomy rather than partial resection 3

Cardiac Considerations in Hyperthyroid Patients

• Beta-blockers should be initiated immediately in hyperthyroid patients with cardiac symptoms (tachycardia, exertional dyspnea, heart failure) to lower heart rate to nearly normal and improve the tachycardia-mediated component of ventricular dysfunction 1
• Hyperthyroidism increases cardiac workload and can precipitate heart failure, especially in older patients with underlying cardiac disease 1
• The hemodynamic changes of hyperthyroidism include increased cardiac output and reduced vascular resistance, which beta-blockers help counteract 1

Management of Burning Mouth Symptoms

Expected Response to Thyroid Treatment

• In patients with thyroid-related burning mouth, 64% showed positive response (VAS 1 or 0) after treatment with thyroid hormone normalization 4
• Oral burning symptoms typically improve within weeks to months of achieving euthyroid state 4
• If burning mouth persists after 3-4 months of normalized thyroid function, consider it primary burning mouth syndrome requiring specific treatment 4, 5

Treatment if Symptoms Persist After Thyroid Correction

• Topical clonazepam and capsaicin demonstrate favorable outcomes in both short-term (≤3 months) and long-term (>3 months) assessment for primary burning mouth syndrome 6
• Alpha-lipoic acid 600 mg/day can be considered, though its effect is modest in short-term but increases with long-term use 6, 5
• Cognitive behavioral therapy shows favorable outcomes in both short- and long-term assessment 6
• Low-level laser therapy demonstrates benefit in both short- and long-term follow-up 6
• Systemic clonazepam or antidepressants may provide relief if topical treatments fail 5

Critical Pitfalls to Avoid

• Never diagnose primary burning mouth syndrome without first evaluating and normalizing thyroid function, as 80.49% of patients with TSH alterations have elevated TSH (hypothyroidism) 2
• Do not use propylthiouracil as first-line antithyroid therapy due to severe hepatotoxicity risk 3
• Avoid exceeding methimazole 20 mg/day initially to minimize agranulocytosis risk 3
• Do not stop antithyroid drugs immediately before radioiodine therapy—wait at least one week to reduce treatment failure 3
• For patients with hyperthyroidism and cardiac disease, failure to initiate beta-blockers can lead to cardiovascular complications including heart failure and arrhythmias 1
• Do not assume burning mouth will resolve immediately with thyroid treatment—allow 3-4 months of euthyroid state before concluding symptoms are unrelated 4, 5