Endocrine Abstracts

Forty-seven years old lady presented to another hospital with symptoms of diarrhea and sleep disturbance. She was found to have abnormal thyroid function tests (TFTs) with fT₄ 44 fT₃ 12 and TSH 3.4. She had no goiter or thyroid eye signs. Thyroid ultrasound showed a multinodular goiter and an uptake scan was consistent with thyrotoxicosis.

She was commenced on carbimazole and in 2001 radio-iodine was administered for a presumed diagnosis of Grave’s disease. She was subsequently diagnosed with hypothyroidism and commenced on levothyroxine. The dose was gradually increased to 350 μg, however TSH remained elevated. In 2006 she was referred to our hospital. TFTs showed elevated TSH 8.5 and fT₄ 38. Heterophile antibodies were negative. Hypothyroid with poor treatment compliance was suspected.

Over the next 2 years adjustments were made to the levothyroxine dose and repeated advice on compliance given. Copies of clinic letters from the first hospital were then obtained with details of initial biochemistry and the diagnosis reviewed. In January 2009 serum calcium was high 3.03 mmol/l with a high parathyroid hormone at 113. Ultrasound and nuclear medicine imaging suggested a left lower pole parathyroid adenoma. MRI scan of the pituitary demonstrated a 4 cm pituitary adenoma with suprasellar extension, compressing the optic chiasm. Biochemical assessment of pituitary function was normal.

Neck exploration was performed and a single left sided parathyroid nodule was removed. Histology demonstrated parathyroid hyperplasia. Two weeks later trans-sphenoidal pituitary surgery was performed. The surgery was complicated by post-operative meningitis. She remains on levothyroxine treatment. Initial genetic testing for MEN1 did not demonstrate a mutation.

TSH-secreting pituitary adenomas are rare and diagnosis could be easily missed. Misdiagnosis and inadvertent thyroid ablation is known to result in the enlargement of TSHomas. Regular and retrospective review of diagnoses can be vital in reaching the correct diagnosis.