From the Guidelines
Methimazole is not effective for treating TSH-secreting adenomas (TSHomas), and the management is different from primary hyperthyroidism. The first-line treatment for TSHomas is typically surgical removal of the pituitary adenoma via transsphenoidal surgery, as recommended by the consensus guideline for the diagnosis and management of pituitary adenomas in childhood and adolescence 1. Unlike primary hyperthyroidism where methimazole blocks thyroid hormone production, TSHomas cause hyperthyroidism due to excessive TSH secretion from the pituitary gland, bypassing normal feedback mechanisms.
Before surgery, somatostatin analogs may be used to control hyperthyroidism by inhibiting TSH secretion, as they have been shown to improve symptoms of thyrotoxicosis, decrease serum-free T4 and TSH concentrations in adults with TSHoma 1. Beta-blockers can help manage symptoms while awaiting definitive treatment. For patients who are poor surgical candidates or have residual disease after surgery, radiation therapy or long-term somatostatin analog therapy may be necessary. Methimazole would be ineffective because it doesn't address the underlying cause of excessive TSH production, and blocking thyroid hormone synthesis could potentially stimulate further TSH secretion from the adenoma.
Key points to consider in the management of TSHomas include:
- Surgical removal of the pituitary adenoma via transsphenoidal surgery as the first-line treatment
- Use of somatostatin analogs to control hyperthyroidism before surgery
- Management of symptoms with beta-blockers while awaiting definitive treatment
- Consideration of radiation therapy or long-term somatostatin analog therapy for patients who are poor surgical candidates or have residual disease after surgery.
From the Research
Management of TSH-Secreting Adenomas
The management of TSH-secreting adenomas, also known as thyrotropinomas, involves a combination of surgical, medical, and radiation therapies.
- Surgical treatment, such as transsphenoidal surgery, is considered the definitive therapy for TSH-secreting adenomas 2.
- Medical treatment includes the use of somatostatin analogs, such as octreotide and lanreotide, which have been shown to be effective in reducing TSH and alpha-subunit secretion, normalizing FT4 and FT3 levels, and restoring the euthyroid state in the majority of patients 3.
- Dopamine agonists, such as bromocriptine and cabergoline, have also been used to treat TSH-secreting adenomas, particularly in patients with combined hypersecretion of TSH and PRL 4, 2.
Role of Methimazole
There is no evidence to suggest that methimazole, a medication commonly used to treat hyperthyroidism, is effective in treating TSH-secreting adenomas.
- In fact, the use of methimazole or other antithyroid medications may not be recommended, as they do not address the underlying cause of the hyperthyroidism, which is the excessive secretion of TSH by the pituitary adenoma 3, 5.
- Instead, treatment should focus on reducing TSH secretion and managing the pituitary adenoma, either through surgical or medical means.
Treatment Outcomes
The outcome of treatment for TSH-secreting adenomas can vary depending on the individual patient and the specific treatment approach used.