Resistance to thyroid hormone (RTH) is an inherited syndrome of reduced tissue responsiveness to free thyroid hormone, which is usually due to mutation in the thyroid hormone receptor beta gene (THRB). Patients may present with symptoms suggesting hyperthyroidism, especially with tachycardia. Lab results may usually be the first clear indication of RTH with results showing the unusual combination of increased free thyroid hormones accompanied by a normal or slightly elevated TSH level. Differentials will include the rare TSH secreting pituitary tumor.
Methods : case study
Here we present a case of a 50 year old African American male with a long standing history of hyperthyroidism, with elevated fT4 and ft3 (confirmed with LCMS) with normal or slightly elevated TSH for the last 4 years, with intermittent symptoms of hyperthyroidism (atrial fibrillation and weight fluctuations) only on symptomatic treatment with beta-blockers. He has no family history of thyroid disease and is not taking any thyroid related supplements. He also has a history of severe heart failure with EF 10-13% and formation of an atrial thrombus since 2014, which corresponds to first recording of abnormal TFTs .Thyroid ultrasound done, back in 2014, showed 2 dominant nodules bilaterally with subsequent thyroid uptake and scan showing a normal uptake of 31%. Anterior pituitary workup and brain MRI were negative for pituitary adenoma. TSI Abs was negative. Alpha subunit, SHBG and TRH-beta gene workup is pending.
Discussion : case study
Patients with resistance to thyroid hormone usually have a benign course with only tachycardia as a presenting symptom. However, the severe cardiac presentation in our patient brings up the possibility that thyroid receptors in the heart in certain populations have a different sensitivity for free thyroid hormones than the rest of the body.
Kansas City, Missouri
Graduate of Tbilisi State Medical University. country of Georgia. Internal medicine training at Wyckoff Heights Medical Center, Brooklyn, NY, graduated in 2018. Fellowship at UMKC- Endocrinology, Diabetes and Metabolism started in 2018.