The Prevalence of Euthyroid Hypertriiodothyroninemia in Newly Diagnosed Multiple Myeloma and its Clinical Characteristics.

Objective: To evaluate the prevalence of euthyroid hypertriiodothyroninemia and/or hyperthyroxinemia and its clinical characteristics in multiple myeloma (MM) patients.

Methods: Previously untreated, newly diagnosed patients with MM were enrolled at the Beijing Chao-yang Hospital between January 2016 and December 2019. Thyroid function and clinical characteristics were analyzed.

Results: A total of 105 patients were enrolled in this study. Thirteen (12.38%) patients exhibited euthyroid hypertriiodothyroninemia with strikingly elevated total triiodothyronine (TT3) levels (>8 ng/mL). Among these 13 patients, 12 patients were immunoglobulin (Ig) G type (92.31%), and 1 patient was light-chain κ type (7.69%). Compared with other patients with MM, patients with hypertriiodothyroninemia were more likely to be IgG type and had higher serum globulin and lower albumin levels and more advanced International Staging System stage (all P < .05). Among the 13 euthyroid hypertriiodothyroninemia patients, 8 patients have been followed up and checked for thyroid function. The TT3 levels in all 8 patients were normalized to the reference range after antimyeloma chemotherapy.

Conclusion: About 12% of patients with MM had euthyroid hypertriiodothyroninemia. Their strikingly elevated TT3 was normalized after chemotherapy. Clinicians should be aware of the possibility of high TT3 levels in euthyroid patients with MM and the potential risk of MM in patients with strikingly elevated TT3.