Endocrine Abstracts

TSHoma is rare, with an incidence of 1 per million, and <1% of all pituitary tumours. We reported a case involving a 49-year-old female who was first referred to our endocrine unit in 2006 with excessive lethargy and abnormal TFT’s. She was thought to have thyroid hormone resistance for several years until 2015 when she reported having persistent symptoms and further investigation suggested an alternative diagnosis.

Results: Ft4=41.6 pmol/l, TSH=4.6 mU/l, alpha subunit <0.3 IU/l (normal <1 IU/l), SHBG=147 nmol/l (normal range 18–114 nmol/l) and sequencing of thyroid hormone receptor β gene showed no abnormalities. Her prolactin was 893mU/l. She complained of excess thirst and high production of dilute urine. Her urine osmolality was 278 mOsm/kg following water deprivation, and post-desmopressin urine osmolality showed a partial urine concentration (607 mOsm/kg). MRI pituitary scan revealed 2 small foci of enhancing lesion (3 mm) consistent with microadenoma.

Diagnosing TSHoma: Patient went on to have a TRH test which showed basal TSH of 1.59 mU/l rising to 2.54 mU/l after 60 minutes. A Methione-PET scan (protocol by Dr Gurnell, Cambridge) showed changes consistent with TSHoma. Octreotide (100 mcg) suppression test demonstrated a reduction in TSH from 1.89 to 0.93 mU/l, five hours after administration.

Management of TSHoma: Sandostatin LAR 20 mg once monthly was initiated which showed normalization of TFT’s (ft4 22.4 pmol/l, ft3 5.1 pmol/l and TSH 0.08 mU/l). However, patient reported probable Sandostatin-related side effects (diarrhoea and abdominal cramps). She underwent transphenoidal pituitary surgery that resulted in stabilization of TFT, however she developed hypoadrenalism post-operatively and was started on steroid therapy.

Conclusion: Biochemical and dynamic tests are required to diagnose TSHoma. PET scan can be useful in definitive localisation of pituitary lesion. Treatments are directed at treating the symptoms secondary to elevated thyroid hormones, however deciding between medical and surgical options require careful consideration of fitness for surgery, co-morbidities and therapeutic complications.