Thyroid Hormone Resistance Syndrome Presenting as Exercise Induced Asthma

Background: Pathogenic variants in the thyroid hormone receptor (THRB) gene are associated with thyroid hormone resistance. Over 85% of the genetic mutations are in the beta TR gene. The disorder is characterized mainly by elevated thyroid hormone levels, unsuppressed levels of TSH, and goiter. Clinical case: An 11-year-old male initially seen at the PCP office for tachycardia and chest discomfort, especially during school exercise. He reported shortness of breath. His symptoms will resolve at rest. He was diagnosed initially with asthma and was put on Singular, Pulmicort, and albuterol as needed. His symptoms did not improve with this treatment, and he reported symptoms worsened with albuterol. He had a normal Echocardiogram and chest X-ray. A mild goiter was noted on his physical exam. Thyroid ultrasound showed an enlarged thyroid gland. An ovoid echogenic focus in the inferior thyroid lobe measuring 4 X 7 X 8mm was identified. The nodule was wider than tall, with a solid appearance with no internal color flow. Evaluation in our clinic showed normal TSH at 1.624mcIU/mL (0.35-5.5). FT4 was high at 1.54ng/dL (0.82-1.40), and FT3 elevated at 6.3pg/mL (3.3-4.8). Thyroid antibodies and thyroid-stimulating immunoglobulin (TSI) were normal. A 24 hour I-123 thyroid uptake was approximately 55% (10-30%) with no focal increased or decreased uptake. Given his elevated thyroid hormone levels with unsuppressed TSH in the context of goiter and tachycardia, genetic testing for the Thyroid receptor gene was done. He was found to be heterozygous for a pathogenic variant in THRB, c.1286G>A (p.Arg429Gln). This genotype is consistent with a diagnosis of autosomal dominant Thyroid hormone resistance. The patient was started on Atenolol, given his elevated heart rate, and he reported improvement in his symptoms during exercise. Conclusion: Thyroid hormone resistance was first described as a clinical entity in 1967. The phenotype can vary among individuals. It is characterized by a reduced responsiveness of target tissue to thyroid hormone and binding affinity. The disease can present with goiter, behavioral issues, abnormal growth, and tachycardia. Affected individuals may have attention deficit-hyperactivity disorders (ADHD) and language difficulties. Thyroid hormone resistance can be misdiagnosed, as in our patient. He was diagnosed with asthma and was put on unnecessary medications that worsened his symptoms. Thyroid hormone resistance can also be misdiagnosed with Graves’ disease, given the elevated thyroid hormone. It is essential to highlight the importance of genetic testing in these cases, as an accurate diagnosis will prevent unnecessary treatments with potentially serious side effects.

Thyroid Hormone Resistance With Concurrent Papillary Thyroid Cancer

Introduction: Thyroid hormone resistance is a genetic mutation resulting in decreased receptor responsiveness. We present a case of thyroid hormone resistance with concurrent papillary thyroid cancer. Clinical Case: A 34-year-old man with a history of papillary thyroid carcinoma status post total thyroidectomy and radioactive iodine. He had transferred his care after moving to our area. He presented with persistently elevated TSH despite ongoing treatment with Levothyroxine 400 mcg daily. Upon presentation the patient reported intermittent palpitations and tremor. Vital signs revealed height of 74 inches, weight of 235 pounds, blood pressure of 112/64, and heart rate of 48. Physical examination revealed a well -healed scar on the neck without palpable lymphadenopathy. Bloodwork revealed TSH of 15.28 mIU/L and Free T4 of 2.8 ng/dL. The patient was maintained on Levothyroxine 400 mcg daily and educated on proper administration of the medication. Two months later, bloodwork revealed a TSH of 9.22 mIU/L with a Free T4 of 3.3 ng/dL. MRI of the pituitary revealed a 4mm hyper-intensity which likely represented a microadenoma. Resistance Thyroid Hormone (RTH) Mutation analysis was ordered which revealed a heterozygous mutation for the Thyroid Hormone Receptor (THR)-Beta gene. The mutation was detected at pArg438His indicating a single nucleotide substitution leading to the replacement of arginine by histidine at the p.438 of the translated protein on exon 10. The patient was maintained on Levothyroxine at 400 mcg daily. Discussion: Thyroid hormone resistance describes a constellation of symptoms from decreased tissue responsiveness to thyroid hormones. Literature reveals the prevalence of THR to be 1 in 40,000 individuals. It occurs due to mutation on the thyroid hormone receptor, most often found on the alpha or beta subunit. Frequently patients present with tachycardia and hyperactivity but it can also present with symptoms suggestive of hypothyroidism and goiter. Risk factors include family history of RTH mutation often with an autosomal dominant inheritance pattern. Patients with an elevated Free T4 with a non-suppressed TSH should be investigated with a genetic analysis of Resistance Thyroid hormone. A positive mutation would confirm the diagnosis. Close monitoring of symptoms as well as thyroid function tests should guide treatment. The concurrent diagnosis of thyroid hormone resistance in conjunction with papillary thyroid carcinoma in our patient is unique and makes management a challenge. The literature reveals few cases reported. Reference: DynaMed. (2018, November 30). Thyroid Hormone Resistance. Retrieved October 2, 2020, from https://www-dynamed-com.arktos.nyit.edu/topics/dmp~AN~T912485 Igata M, et al. Coexistence of resistance to thyroid hormone and papillary thyroid carcinoma. Endocrinol Diabetes Metab Case Rep. 2016;2016:160003. doi:10.1530/EDM-16-0003

Coexistence of Thyroid Hormone Resistance and Autoimmune Thyroid Disease: Not a Mere Coincidence

Introduction: The coexistence of thyroid hormone resistance and autoimmune thyroiditis was initially thought to be a chance event. In a large cohort study, Barcoff et al. demonstrated an increased likelihood of thyroid autoantibodies in patients with thyroid hormone resistance (RTH). We report a unique case to epitomize the coexistence of these two conditions and discuss the postulated mechanisms. Clinical Case: A 22-year-old woman with a history of Hashimoto’s thyroiditis, attention deficit hyperactivity disorder, and migraine presented to the endocrinology clinic with symptoms of weight loss, fatigue, decreased appetite, and heat intolerance for 4 months. She was diagnosed with Hashimoto’s thyroiditis at age 12 with elevated TSH only and had been on levothyroxine 25 mcg since diagnosis. Physical exam demonstrated a body mass index of 34.14 kg/m2, blood pressure of 138/91 mmHg, pulse of 77 bpm, and an enlarged palpable thyroid gland. Laboratory investigations revealed elevated thyroid peroxidase (TPO) antibody at 234 IU/mL (<9) and thyroglobulin Antibody at 3 IU/mL (<1) with elevated free T4 of 3.76 ng/dL (0.61-1.36), elevated total T4 of 21.58 mcg/dL (6.09-12.23), increased T3 uptake of 51.2% uptake (32-48.4), and upper normal TSH of 3.99 uIU/mL (0.44-5.33). Elevated free T4 was confirmed by the equilibrium dialysis method at 6.2 ng/dL (0.9-2.2) with upper normal TSH at 3.77 uIU/mL. Thyroid ultrasound demonstrated thyromegaly and hypervascularity of the gland. TSH secreting pituitary adenoma was ruled out with a normal alpha subunit of 0.2 ng/ml (0.1-0.6) and molar ratio of the alpha subunit to TSH ratio <1 along with a normal pituitary MRI. She was not taking other medications or supplements. She was diagnosed with thyroid hormone resistance and is undergoing genetic testing to differentiate the THRB genetic mutations from Non-TR-RTH. Her symptoms improved after discontinuing her levothyroxine. Clinical Lesson: Our case highlights the importance of evaluating thyroid disorders properly before starting treatment and illustrates the coexistence of autoimmune thyroiditis with thyroid hormone resistance. Barcoff et al. demonstrated that there was an increased likelihood of thyroid autoantibodies with odds ratio = 2.36 (p = 0.002) in a large patient cohort with RTH, compared to their unaffected first-degree relatives. However, since there was no correlation in increased antibody with increased age and the duration of the disease, the proposed hypothesis did not substantiate chronic TSH stimulation inducing autoimmune response. The proposed mechanism is that the elevated TSH in RTH stimulates the immune system at the TRα level which was demonstrated in murine models with increased activation of thymic function in correlation with TSH level. More research is needed to understand the underlying mechanism of their coexistence.