Abstract

Introduction: Thyroid hormone resistance(THR) is an end organ hyporesponsiveness in tissues. And systolic time interval index (Preejection period / Left ventricular ejection time) is a useful and alternative way to follow up metabolic and tissue effects of the thyroid hormone.
Case Presentation: A 72 year old male patient had been referred to Akdeniz University Endocrinology Division because of high thyroid hormone levels on routine screening. He had elevated thyroid hormone levels accompanied with tachycardia. He had no hand fine tremor. His hypophyseal MRI had normal appearance. His thyroid autoantibody tests were in negative limits. His systolic time interval index was 0,185 (0.29-0.34) before treatment. He was evaluated as thyroid hormone resistance. After one month of methimazole treatment, his systolic time interval index increased up to 0,238. His TSH, free T4, free T3 levels were 26.59 μIU/mL (0.35-5.5), 0.89 ng/dL(0.89-1.76) and 3.05 pg/mL(2.3-4.2) respectively following treatment. And he had no longer tachycardia.
Conclusion: Misdiagnosis of THR in clinics are common and it causes treatment failures in patients. And systolic time interval index measurement is also a reliable way to follow-up treatment of hyperthyroxinemia.