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A rare presentation of TSH-secreting Pituitary macroadenoma (TSHoma) alongside an Autoimmune Primary Hypothyroidism -The management challenge

A Khan, AD Rajgor, University Hospitals of North Midlands

Thyrotropin-secreting pituitary adenomas (TSHomas) and Primary Hypothyroidism rarely present simultaneously.

We present a 46-year-old woman with both an autoimmune primary hypothyroidism (TPO +ve) and a newly detected TSHoma. This lady having primary hypothyroidism, on Levothyroxin for 3 years, presented with secondary amenorrhoea. The pituitary profile indicated raised prolactin level of 2750 µg/L. Rest of the pituitary profile was normal. MRI scan demonstrated pituitary macroadenoma with no evidence of mass effect or optic chiasm compression. She was already started on Cabergoline 250 microgram twice/week. Subsequently she was discussed at our multi-disciplinary meeting. This led to a diagnosis of a non-functioning pituitary macroadenoma with hyperprolactinaemia. The hyperprolactinaemia was thought to be a consequence of pituitary lactotroph disinhibition and pituitary insufficiency rather than a prolactinoma. Despite Cabergoline treatment reducing the prolactin levels (<10 µg/L) the mass persisted in size. Additionally, despite persistent treatment with levothyroxine at increasing doses (200 micrograms OD) the TSH (TSH 7.12 mU/L, T4 24.87 pmol/L) was not supressed appropriately. Subsequently, she became clinically thyrotoxic with weight loss and thus levothyroxine was stopped. Her thyroid profile (TSH 67.03 mU/L, T4 7 pmol/L) after stopping levothyroxine provided a high suspicion of a TSHoma.

She was subsequently re-discussed at the MDT, where it was decided a transsphenoidal hypophysectomy would be in her best interest. Following a detailed explanation of the treatment options to the patient, she decided to opt for surgery and Transsphenoidal hypophysectomy was performed. Histopathological examination confirmed a TSHoma. Post operatively she became clinically hypothyroid and has thus restarted levothyroxine (100micrograms OD) with a stable thyroid profile (TSH 0.43 mU/L, T4 21pmol/L). This patient is currently recovering well and “feeling great.”

Conclusions/Learning Points: This case demonstrates a very rare phenomenon where a patient has both autoimmune hypothyroidism and a TSHoma. This makes biochemical and clinical analysis very problematic. Biochemically this patient had an elevated TSH and low/normal T4 and despite levothyroxine treatment the TSH would not be suppressed. The presence of a potentially autoimmune primary hypothyroidism masked the appearance of a TSHoma. The autoimmune hypothyroidism (raised TSH, low T4, TPO antibodies +ve) required levothyroxine but the TSHoma was already stimulating the thyroid gland resulting in secondary thyrotoxicosis. It is possible that she had a degree of primary hypothyroidism with Hashimoto’s thyroiditis and now she has secondary hyperthyroidism making the clinical and biochemical picture very complicated.

Figure 1: Large Pituitary Macroadenoma (MRI scan)