Introduction
We present a case of hyperthyroxinemia, decompensated idiopathic heart failure, and pituitary adenoma to discuss the diagnostic and management challenges in differentiating between thyroid stimulating hormone (TSH) producing pituitary adenoma and thyroid hormone resistance (RTH).
Case: A 58-year-old man with a three-year history of idiopathic non-ischaemic dilated cardiomyopathy with moderate to severe left ventricular failure, was brought into the emergency department with NYHA class IV heart failure. Family history remarkable for brother treated for Graves’ disease with radioactive iodine over 20 years ago, subsequent reassessment for elevated TSH while on thyroxine replacement was found to have heterophile antibodies.
Our patient presented frail BMI 18 kg/m2, relative tachycardia (85 beats per minute on beta blockade), with a small palpable goitre. Laboratory investigations without iodinated contrast or biotin revealed elevated thyroid hormone levels (free T4: 44 pmol/L, free T3: 9.2 pmol/L) with an inappropriately normal TSH: 3.19 mIU/L (Roche). The result was reproducible on an alternative platform (Siemens), heterophile antibodies studies and dilution test negative. Elevated sex hormone binding globulin: 133 nmol/L (10-45 nmol/L). Alpha subunit: TSH ratio increased to 1.14 (<1). MRI revealed a 5mm right pituitary adenoma. TSH receptor antibody negative and other anterior pituitary hormones normal. Dynamic testing with a T3 suppression test was not appropriate due to his cardiac decompensation. SHBG, alpha subunit: TSH ratio and MRI were suggestive of a diagnosis of thyrotropin-secreting tumor (TSHoma).
Carbimazole was started due to concern that hyperthyroidism may be contributing to his decompensating cardiac failure while waiting for further investigation. Thyrotropin-releasing hormone stimulation test done withholding carbimazole for 10 days and family history both suggestive of RTH.
THRbgene pathogenic mutation (c.1357c>a) was found and he was diagnosed with RTH. Unfortunately, our patient within a day of discharge to a nursing home died suddenly. A limited post-mortem request has been requested.