Original ArticleThe Prevalence of Euthyroid Hypertriiodothyroninemia in Newly Diagnosed Multiple Myeloma and its Clinical Characteristics
Introduction
In the evaluation of thyroid function and analysis of total triiodothyronine (TT3), free triiodothyronine (FT3), total thyroxine (TT4), free thyroxine (FT4), and thyrotropin (TSH) are widely and routinely used for diagnosis. Most iodothyronines bind reversibly to serum proteins. Approximately 99.97% of T4 and 99.7% of T3 bind to these 3 proteins—thyroxine-binding globulin (TBG), transthyretin (or thyroxine-binding prealbumin), and albumin.1,2 Changes in these binding proteins can cause abnormalities in the test results of total thyroid hormone concentration with or without normal FT3 and FT4 levels in the serum. TBG abnormalities are the most frequent causes.3 Nevertheless, other types of interferences are known to affect the measurements of thyroid hormones, such as thyroid hormone autoantibodies, antistreptavidin antibodies, antiruthenium antibodies, heterophilic antibodies, and biotin.4
Multiple myeloma (MM) is a neoplastic hematologic disorder that is characterized by the clonal proliferation of malignant plasma cells in the bone marrow and monoclonal immunoglobulin (Ig) in the blood or urine.5 To the best of our knowledge, till date, 3 patients with MM, who were characterized as clinically euthyroid but with extremely elevated TT3 or TT4 levels and normal FT3, FT4, and TSH levels, have been reported from different medical centers.6, 7, 8 These studies indicated that elevated monoclonal Ig can bind to T3 or T4 and interfere in the results of thyroid function tests in MM. However, the prevalence of euthyroid patients with elevated total thyroid hormones in MM and its clinical characteristics is unknown.
This study was performed to analyze the thyroid function in newly diagnosed MM and the change in the function after the treatment of MM.
Section snippets
Subjects
Patients with untreated and newly diagnosed MM were consecutively enrolled at our hospital from January 2016 to December 2019. All patients met the diagnostic criteria of MM defined by the International Myeloma Working Group.9 Patients who had a preexisting history of hyperthyroidism or hypothyroidism or had taken medicines known to influence thyroid function, patients who had severe liver or renal function impairment, and patients who had severe infection or other malignant tumors were
Clinical Characteristics of Studied Subjects
Of the 105 patients included in this study, 56 were men (53.33%). The mean age at diagnosis with MM was 62.98 ± 9.79 years. In all enrolled patients, 59 (56.19%) patients were IgG type, 18 (17.14%) patients were IgA type, 5 (4.76%) patients were IgD type, 19 (18.10%) patients were only light-chain secretory, and 4 (3.81%) patients were nonsecretory. A total of 13 patients (12.38%) had strikingly elevated TT3 levels (TT3 >8 ng/mL, reference range, 0.60-1.81 ng/mL) and were assigned to group A (n
Discussion
Our study found that 13 (12.38%) of the 105 patients with MM had strikingly elevated TT3 levels (>8 ng/mL, reference range, 0.60-1.81 ng/mL). No patients had any symptoms or signs of hyperthyroidism. Compared with other myeloma patients, hypertriiodothyroninemia patients were more likely to be IgG type and had higher globulin levels and more advanced ISS stage. Among all the patients who were followed up, the TT3 levels that were >8 ng/mL at baseline were normalized to the reference range after
Acknowledgment
This study was funded by grants from the Beijing Hospitals Authority Youth Programme (code: QML20160304) to Qingrong Pan, the National Natural Science Foundation of China (No. 81770792), and the Capital Clinical Research Foundation of Beijing Municipal Commission of Science and Technology, China (No. Z161100000516069) to Guang Wang.
Author Contributions
Q.P. and Y.Z. contributed equally to this work.
Disclosure
The authors have no multiplicity of interest to disclose.
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