Clinical outcomes of 34 patients with resistance to thyroid hormone beta: a twenty-year experience in Japan

Resistance to thyroid hormone beta (RTHI3) caused by germline mutations in genes encoding thyroid hormone receptor beta (TRI3) is a rare disorder. Little information is available regarding the clinical experience of this syndrome in Japan. We retrospectively reviewed the records of 34 patients with RTHI3 (21 adult females and 13 adult males) with positive TRI3 mutations identified at our division between 2000 and 2020. Of the 24 patients with available clinical history, 10 (41.7%) received inappropriate treatments such as antithyroid drugs, thyroidectomy, or radioactive iodine. Diagnostic delay and inappropriate management of RTHI3 are still present in Japan. Every patient except one demonstrated thyroid hormone profiles indicative of syndrome of inappropriate secretion of thyrotropin (SITSH), characterized by a hormonal profile of hyperthyroxinemia with a non-suppressed TSH concentration. Since the most common forms of hyperthyroidism including Graves' disease feature elevated thyroid hormone levels with suppressed TSH concentrations, early diagnosis of SITSH is critical for preventing inappropriate management. One patient positive for anti-thyroglobulin antibody (Tg-Ab) and anti-thyroperoxidase antibody (TPO-Ab) showed remarkably elevated TSH (>200 mu IU/mL) despite thyroid hormone concentrations within the reference ranges. At least one thyroid autoantibody (Tg-Ab, TPO-Ab, or thyrotropin receptor antibodies) was identified in 37.9% (11/29) of the patients tested. One patient developed overt Graves' disease nine years after RTHI3 diagnosis. These findings suggest that RTHI3 is frequently comorbid with additional autoimmune thyroid disorders. Further research is required to identify the most appropriate treatments for RTHI3 patients who develop a second thyroid disorder.