A Diagnostic Masquerade: Resistance to Thyroid Hormone Mimicking TSH-Secretory Pituitary Adenoma
https://doi.org/10.15605/jafes.041.S1
- Author:
Deviga Lachumanan
1
Author Information
1. Department of Medicine, Hospital Port Dickson
- Publication Type:Journal Article
- MeSH:
Pituitary Neoplasms;
Thyroid Hormones;
Thyrotropin
- From:
Journal of the ASEAN Federation of Endocrine Societies
2026;41(S1):119-
- CountryPhilippines
- Language:English
-
Abstract:
Introduction:Discordant thyroid function tests (TFTs), characterized
by elevated free thyroxine 4 (FT4) with non-suppressed
thyroid-stimulating hormone (TSH), pose a significant
diagnostic challenge. Differentiating between Resistance
to Thyroid Hormone (RTH) and TSH-secreting pituitary
adenoma (TSH-oma) is essential, as management strategies
differ substantially.
Case:A female with a history of hyperthyroidism diagnosed in
2011 was treated with antithyroid drugs for 1 year before
defaulting on follow-up. She was later found to have
discordant TFTs at a private centre, where a brain computed tomography scan was reportedly normal. She was referred
to our centre for optimization of thyroid function prior
to planned thyroidectomy for a solitary large right
thyroid nodule measuring 4.2 × 2.8 × 4.7 cm. Fine-needle
aspiration cytology demonstrated a benign follicular lesion
(Bethesda II).
Despite restarting antithyroid medication, she remained
clinically euthyroid with no overt thyrotoxic symptoms
apart from intermittent palpitations without documented
tachycardia. Antithyroid therapy was discontinued.
Serial TFTs across multiple assay platforms consistently
demonstrated elevated FT4 with inappropriately normal
TSH levels. Thyroid autoantibodies, including TSH receptor
and anti-thyroid peroxidase antibodies, were negative.
Pituitary magnetic resonance imaging showed no evidence
of adenoma, and serum α-subunit level was normal (0.3 ng/
mL), making TSH-oma unlikely. Dynamic testing was not
performed as thyrotropin-releasing hormone stimulation
was unavailable at our centre, while T3 suppression testing
was deemed inappropriate due to symptomatic palpitations. Family screening was not possible as the patient
was not in contact with her relatives. In the absence of
pituitary pathology and given her largely euthyroid clinical
status, RTH was considered the most likely diagnosis.
Conclusion:This case highlights the importance of considering RTH
in patients with persistent discordant TFTs, particularly
when clinical findings do not correlate with biochemical
abnormalities. Early recognition and appropriate pituitary
evaluation are essential to prevent misdiagnosis and avoid
unnecessary antithyroid therapy or thyroidectomy.
- Full text:2026080509494213756EP_A178.pdf
