Objective : TSH producing pituitary adenoma is an extremely rare etiology of hyperthyroidism whereas autoimmune thyroiditis is a common cause of hypothyroidism. The association of TSH producing pituitary adenoma with autoimmune thyroiditis and hypothyroidism has been rarely reported in the literature but its development can effectively treat the patient of the hyperthyroid state. A 29 years old lady with no known medical illness presented to obstetrician with exertional dyspnoea and palpitations at 14 weeks of pregnancy. Thyroid function test showed fT4 of 36 pM (RI: 8-21) and TSH of 4.99mIU/L (RI: 0.34-4.5). 100 mg of Propylthiouracil was started and subsequently was discontinued after delivery. However her symptoms persisted and her thyroid function test constantly showed elevated fT4 with non-suppressed TSH concentrations. Two weeks after delivery her fT4 was 34pM and TSH was 5.99 mIU/L. She was tachycardic with a pulse rate of 105/min and blood pressure of 120/76 mmHg. There was no goitre or any sign of thyroid eye disease. A repeat thyroid function tests showed fT4 of 24.9 pM, TSH of 8.52 mIU/L, fT3 of 16.9 pM (RI: 4.3-8.3), TRAb of 0.4 IU/L (RI: 0-1.5 ), and TPO Ab of 2253 IU/ml (RI < 50). The working diagnosis at this point was TSH resistance syndrome versus TSH producing pituitary adenoma. An MRI of the pituitary showed a 2.5 x 2.4 mm microadenoma in the left anterolateral aspect of the pituitary gland. Before any further dynamic tests could be done, 2 months later, she presented with weight gain of 4 kg and with pulse rate of 62/minute and blood pressure of 114/66 mmHg. Her thyroid function test showed fT4 of 3.5 pM and TSH of 19.34 mIU/L and a subsequent test 2 weeks later showed fT4 of 2.2 pM and TSH of 38.22mIU/L suggestive of hypothyroidism likely secondary to autoimmune thyroiditis. She was started on thyroxine and the dose was titrated up to 100 mcg daily. Approximately 3 months after initiation of thyroxine 100 mcg daily, her fT4 was 12.0 pM and TSH was 9.26mIU/L.
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Results : N/A
Discussion : TSH secreting adenomas are rare lesion of pituitary and are the least common of the secretory adenomas. They occur in 1-3% of large series of the pituitary adenomas, TSH secreting pituitary adenomas tend to present much later in women and tumors tend to be very small with few symptoms.
Conclusion : The association of Hashimoto's thyroiditis developing after presentation of a TSH producing pituitary adenoma results in the biochemical remission of hyperthyroidism but the lowering of thyroid hormone level from hypothyroidism may result in an increase in the size of the pituitary adenoma over years. Hence this patient will need to be followed up closely.
Chee Kian Chew– Consultant, Tan Tock Seng Hospital, Singapore