Agoitrous Graves’ Hyperthyroidism with Markedly Elevated Thyroid Stimulating Immunoglobulin Titre displaying Rapid Response to Carbimazole with Discordant Thyroid Function

Yin Chian Kon; Brenda Su Ping Lim; Yingshan Lee; Swee Eng  Aw; Yoko Kin Yoke Wong

doi:10.15605/jafes.035.02.13

Authors

Yin Chian Kon Tan Tock Seng Hospital https://orcid.org/0000-0002-9693-2587
Brenda Su Ping Lim Tan Tock Seng Hospital https://orcid.org/0000-0003-2768-285X
Yingshan Lee Tan Tock Seng Hospital https://orcid.org/0000-0001-9381-8079
Swee Eng Aw Singapore General Hospital
Yoko Kin Yoke Wong Singapore Clinical Research Institute https://orcid.org/0000-0002-1276-7060

DOI:

https://doi.org/10.15605/jafes.035.02.13

Keywords:

Graves' disease, Thyroid Stimulating Immunoglobulin, responsiveness, carbimazole

Abstract

We characterize the clinical and laboratory characteristics of 5 patients with Graves’ thyrotoxicosis whose serum free thyroxine (fT4) concentration decreased unexpectedly to low levels on conventional doses of carbimazole (CMZ) therapy. The initial fT4 mean was 40.0 pM, range 25-69 pM. Thyroid volume by ultrasound measured as mean 11 ml, range 9.0-15.6 ml. Initial TSI levels measured 1487% to >4444%. Serum fT4 fell to low-normal or hypothyroid levels within 3.6 to 9.3 weeks of initiating CMZ 5 to 15 mg daily, and subsequently modulated by fine dosage adjustments. In one patient, serum fT4 fluctuated in a “yo-yo” pattern. There also emerged a pattern of low normal/low serum fT4 levels associated with discordant low/mid normal serum TSH levels respectively, at normal serum fT3 levels. The longterm daily-averaged CMZ maintenance dose ranged from 0.7 mg to 3.2 mg. Patients with newly diagnosed Graves' hyperthyroidism who have small thyroid glands and markedly elevated TSI titres appear to be “ATD dose sensitive.” Their TFT on ATD therapy may display a “central hypothyroid” pattern. We suggest finer CMZ dose titration at closer follow-up intervals to achieve biochemical euthyroidism.

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Author Biographies

Yin Chian Kon, Tan Tock Seng Hospital

Department of Endocrinology

Brenda Su Ping Lim, Tan Tock Seng Hospital

Department of Endocrinology

Yingshan Lee, Tan Tock Seng Hospital

Department of Endocrinology

Swee Eng Aw, Singapore General Hospital

Department of Nuclear Medicine and Molecular Imaging

Yoko Kin Yoke Wong, Singapore Clinical Research Institute

Department of Epidemiology

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