Endocrine Abstracts

Introduction: TSH-secreting pituitary adenomas (TSHomas) are rare pituitary tumours treated primarily with surgery; in cases of surgical failure, somatostatin analogue (SSA) or radiotherapy are further options. SSAs are rarely used as monotherapy; if responsive and in the absence of radiotherapy, the requirement of life-long medical treatment, is unknown. Herein, we present a patient with a TSHoma who remains in remission three years after SSA withdrawal.

Case: A 29-year-old female was referred to the Endocrine Department in 2002 with deranged thyroid function tests; TSH 1.4mIU/l (0.4-5.5), FT4 30.2 pmo/l (9.0-20.0), and FT3 10.9 pmo/l (3.5-6.5). She initially presented to her GP with fatigue and hot flushes; her medical, family, drug history was unremarkable. Positive examination findings included mild tremor and a small palpable goitre only. Repeat testing confirmed hyperthyroxinaemia with inappropriate TSH secretion; screening for antibodies, analytical interference or familial dysalbuminaemia hyperthyroxinaemia was negative. FT4 by equilibrium dialysis was 55.6 pmo/l (10-36 pmo/l). Alpha subunit (α-SU) was 0.45IU/l (<1.0). Anterior pituitary screen was otherwise unremarkable. MRI pituitary demonstrated a 7x7x9 mm adenoma. A trial of octreotide 50 mg subcutaneously thrice daily was started; three weeks later, TSH, T4 and T3 fell from 3.2 mU/l, 28.2 pmo/l, and 10.8 pmo/l to 0.6 mIU/l, 16.5 pmo/l and 5.7 pmo/l, respectively, suggesting a TSHoma. The patient declined pituitary surgery, instead choosing monthly long-acting SSA injections. On this treatment, she remained euthyroid for 16 years and MRI surveillance showed tumour shrinkage with no identifiable surgical target. In 2019, SSA was withdrawn; three years later, she remains biochemically euthyroid with stable MRI appearances.

Discussion: To our knowledge, this is the second reported case of a TSHoma with sustained remission after SSA monotherapy withdrawal. Given limited experience on this management approach, optimal treatment duration is unknown; our case demonstrates that re-assessment of the long-term requirement of SSA monotherapy needs to be considered in these cases.