Differential Diagnosis:
The differential diagnoses for this case include a TSH-secreting
pituitary adenoma (TSHoma), which is supported by the elevated FT4 and
FT3 levels, persistent hyperthyroid symptoms, and the sellar mass on
MRI, making it the most likely diagnosis. Resistance to thyroid hormone
(RTH) is another consideration, as it can cause elevated thyroid
hormones with unsuppressed or high TSH, but typically lacks the clinical
symptoms of hyperthyroidism, such as tachycardia and tremors, and does
not show a pituitary mass on imaging. Exogenous thyroid hormone
ingestion (factitious thyrotoxicosis) could also lead to high FT4 and
FT3, but would typically suppress TSH and is unlikely to be associated
with a pituitary mass. Lastly, multinodular goiter with autonomous
thyroid function could cause elevated thyroid hormones with a mildly
elevated TSH, but this diagnosis is improbable due to the absence of
multinodular findings