THYROTOXICOSIS WITH DISCORDANT THYROID FUNCTION TESTS

A RARE PITUITARY TUMOR PRESENTING WITH THYROTOXIC CARDIOMYOPATHY

Abstract

INTRODUCTION
Thyrotoxicosis can lead to life-threatening complications, including thyroid storm and thyrotoxic cardiomyopathy. Discordant thyroid function tests (TFTs) in severe thyrotoxicosis raise suspicion for atypical causes such as assay interference, pituitary pathology, or ectopic thyrotropin (TSH) secretion.

CASE
A 29-year-old male presented with a two-week history of cough, dyspnea, and palpitations. On admission, he was hemodynamically stable but had bibasal fine crepitations, bilateral pedal edema and signs of thyrotoxicosis (agitation, fine tremors, and hyperreflexia). Cardiac monitoring revealed atrial fibrillation with a heart rate >150 bpm. Thyroid function tests showed discordant TSH 14.92 Miu/L, T4 65.9 pmol/L and T3 13.47 pmol/L levels. He was treated as a case of thyroid storm with thyrotoxic cardiomyopathy.

Echocardiography confirmed heart failure with reduced ejection fraction (20%) and pulmonary artery systolic pressure of 48 mm Hg. Further workup ruled out Group 2, 3, 4 Pulmonary Hypertension (PH) and no invasive right heart catheterization was done. Assay interference was excluded, thyroid autoantibodies were negative and other pituitary hormones were normal. Pituitary MRI showed a large pituitary mass, raising suspicion for the presence of a TSH-secreting pituitary adenoma.

He is currently managed with the anti-thyroid drug methimazole, anti-heart failure medications and anticoagulation by a multidisciplinary team.

TSH-secreting pituitary adenomas (TSHomas) are rare, causing autonomous TSH secretion unresponsive to negative feedback. Unlike resistance to thyroid hormone (RTH), TSHomas typically present with overt hyperthyroidism and tumor-related symptoms (visual defects, headaches, anterior pituitary dysfunction). Atrial fibrillation and heart failure are rare in TSHomas but were prominent in this case. Transsphenoidal surgery is the preferred treatment, resulting in thyroid function normalization in 80% of cases. However, TSHomas often exhibit aggressive invasion, affecting surgical success. If surgery fails, somatostatin analogs (SSAs) can normalize TSH and reduce tumor size.

CONCLUSION
This case highlights the need to consider causes of atypical thyrotoxicosis when TFTs are discordant. Early recognition and a multidisciplinary approach are crucial for managing thyrotoxic cardiomyopathy and its underlying etiology.