Image legend
A 20-year-old woman with no prior medical history presented with complaints of fatigue, weight gain, and neck swelling. Physical examination revealed diffuse goiter without thyrotoxic symptoms or ophthalmopathy. Laboratory tests showed a thyroid-stimulating hormone (TSH) level of >100.0 mIU/L (reference range [RR]: 0.27-4.2 mIU/L), free thyroxine of 0.37 ng/dL (4.8 pmol/L) (RR: 0.8-1.68 ng/dL; 10.3-21.6 pmol/L), and free triiodothyronine of 1.8 pg/mL (2.8 pmol/L) (RR: 2.0-4.4 pg/mL;3.1-6.8 pmol/L). Thyroid peroxidase antibody was elevated (235 IU/mL; RR, <34 IU/mL), with positive thyroid-stimulating immunoglobulin (4.42 index; RR, 0-1.3 index) and TSH receptor-blocking antibodies (5.89 IU/L; RR, 0-1.75 IU/L). Ultrasonography showed diffuse goiter with heterogeneous hypoechoic parenchyma, and 99mTc-pertechnetate scintigraphy revealed diffuse increased uptake with suppressed background activity, mimicking diffuse toxic goiter (Fig. 1). Autoimmune thyroid disease was diagnosed; levothyroxine initiated. Previous studies have demonstrated that coexisting stimulating and blocking TSH receptor antibodies (TRAbs) may produce variable clinical phenotypes and heterogeneous scintigraphicpatterns [1, 2]. This case highlights a discordant phenotype of severe hypothyroidism with diffuse thyroid uptake due to coexisting stimulating and blocking TRAbs. Awareness of this complex antibody interplay is important to avoid misinterpretation of scintigraphic findings, although this discordance does not alter treatment or clinical outcome.
Contributors
S.B.A. was responsible for the clinical evaluation and management of the patient, interpretation of the clinical, laboratory, and scintigraphic findings, conception of the report, and critical revision of the manuscript.
Funding
No public or commercial funding.
Disclosures
The author has nothing to disclose.
Informed patient consent for publication
Signed informed consent was obtained directly from the patient.
References
- 1. Hirose R, Noh JY, Watanabe N, et al. Clinical outcomes of thyroid function in patients with thyrotropin receptor blocking antibody-positive hypothyroidism. J Endocr Soc. 2026;10(8):bvag147. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2. Kasagi K, Hatabu H, Miyamoto S, et al. Scintigraphic findings of the thyroid in hypothyroid patients with blocking-type TSH-receptor antibodies. Eur J Nucl Med. 1994;21(9):962‐967. [DOI] [PubMed] [Google Scholar]