THYROID FUNCTION TESTS: A REVIEW

Thyroid function tests are one of the most common endocrine panels in general practice because a good understanding of when to order them, indications for treatment are important for the optimal treatment of thyroid dysfunction. Thyroid-stimulating hormone (TSH) should be the rst test to be performed on any patient with suspected thyroid dysfunction and in follow-up of individuals on treatment. It is useful as a rst-line test because even small changes in thyroid function are sufcient to cause a signicant increase in TSH secretion. Thyroxine levels may be assessed in a patient with hyperthyroidism, to determine the severity of hyperthyroxinemia. Antithyroid peroxidase measurements should be considered while evaluating patients with subclinical hypothyroidism and can facilitate the identication of autoimmune thyroiditis during the evaluation of nodular thyroid disease. The measurement of TSH receptor antibody must be considered when conrmation of Graves’ disease is needed and radioactive iodine uptake cannot be done.

Graves’ Disease

Graves’ disease is an autoimmune disease characterized by hyperthyroidism due to circulating autoantibodies. Graves’ disease was originally known as “exophthalmic goiter” but is now named after Sir Robert Graves, an Irish doctor who first described the condition in 1835. A number of conditions can cause hyperthyroidism, but Graves’ disease is the most common, affecting around 1 in 200 people. It most often affects women under the age of 40, but it is also found in men. It affects an estimated 2–3 percent of the world’s population. Thyroid-stimulating immunoglobulin (TSIs) binds to and activates thyrotropin receptors, causing the thyroid gland to grow and the thyroid follicles to increase synthesis of thyroid hormone. The overproduction of thyroid hormones can have a variety of effects on the body causes exophthalmic goiter, graves ophthalmopathy, graves dermopathy etc.,. Thyroid profile including antithyroid antibodies, radioactive iodine uptake study, and thyroid scan are the main diagnostic investigations to rule out Graves’ disease. The major aim of the treatment is to inhibit the overproduction of thyroid hormones by targeting the thyroid gland, to reduce the symptoms, and prevention of complication is also major challenges.

Causes of False-Positive Radioactive Iodine Uptake in Patients with Differentiated Thyroid Cancer

Purpose Radioactive iodine (RAI) whole-body scan is a sensitive imaging modality routinely used in patients with differentiated thyroid cancer to detect persistent and recurrent disease. However, there can be false-positive RAI uptake that can lead to misdiagnosis and misclassification of a patient’s cancer stage. Recognizing the causes of false positivity can avoid unnecessary testing and treatment as well as emotional stress. In this review, we discuss causes and summarize various mechanisms for false-positive uptake. Recent Findings We report a patient with differentiated thyroid cancer who was found to have Mycobacterium avium complex infection as the cause of false-positive RAI uptake in the lungs. Using this case example, we discuss and summarize findings from the literature on etiologies of false-positive RAI uptake. We also supplement additional original images illustrating other examples of false RAI uptake. Summary False-positive RAI uptake may arise from different causes and RAI scans need to be interpreted in the context of the patient’s history and corresponding cross-sectional imaging findings on workup. Understanding the potential pitfalls of the RAI scan and the mechanisms underlying false uptake are vital in the care of patients with differentiated thyroid cancer.

CONVERSION OF HYPOTHYROIDISM TO HYPERTHYROIDISM: A RARE CLINICAL PHENOMENON

Objective: We present a patient with long standing hypothyroidism who developed hyperthyroidism secondary to Graves disease. Recognition of this disease phenomenon is crucial to ensure prompt diagnosis and close follow-up. Methods: The patient was evaluated with thyroid function testing and thyroid antibody testing. Further evaluation included ophthalmologic examination and radioactive iodine uptake imaging. Results: A 56-year-old female with past medical history of human immunodeficiency virus, hepatitis C infection, and hypothyroidism presented for evaluation of thyroid disease. She had been off of levothyroxine for the last 8 months due to biochemical findings of thyrotoxicosis. Her family history was significant for hyperthyroidism and hypothyroidism. Laboratory tests were consistent with hypothyroidism so levothyroxine was restarted. Physical exam showed lid lag and proptosis. Ophthalmologic evaluation found bilateral 23 mm proptosis. Additional lab testing was positive for thyroid peroxidase antibody and thyroid stimulating immunoglobulin. Following levothyroxine use, the patient developed subclinical hyperthyroidism and thyroid replacement was stopped. The patient remained euthyroid for 1 year off of levothyroxine. Following 1 year, she developed mild hyperthyroidism with increased radioactive iodine uptake. She was placed on propranolol for symptomatic relief. Months later, thyroid function testing normalized. Conclusion: In Graves disease, hypothyroidism and conversion of hypothyroidism to hyperthyroidism are rare, yet important to recognize, clinical phenomenon. The stimulatory and inhibitory properties of thyroid-stimulating hormone receptor antibodies are speculated to play a role in individuals with alternating hypothyroidism and hyperthyroidism. These individuals can present a diagnostic and therapeutic challenge. Clinicians must maintain a high clinical suspicion for this disease entity.

SUN-516 Unplanned Pregnancy Post Thyroid RAI Ablation

A patient’s pregnancy and fetus are at an increased risk for complications secondary to history of recent RAI ablation and maternal secondary hypothyroidism. A 31 year old female with a recent history of miscarriage presented with abnormal thyroid function tests and was history of low dose levothyroxine use. She complained of a 3 month history of extreme fatigue, palpitations and 18 pound weight loss at the time of presentation. Her thyroid stimulating immunoglobulin was 9.21 IU/L (0-0.55), free thyroxine 6.2ng/dL (0.9-1.8), free triiodothyronine 20.04 pg/mL (1.8-4.6) with a suppressed TSH 0.01 uIU/ml (0.27 - 4.2). She was started on methimazole. Her 24 hour radioactive iodine uptake was 60% and she subsequently underwent radioactive iodine-131 ablation in capsule form. She failed the ablation after 7 months and remained on methimazole during that duration. Her second radioactive iodine uptake was 58% and she underwent a second RAI ablation. Her TSH was 50 uIU/ml and her free thyroxine was 0.1 ng/dl. She was started on levothyroxine for replacement. Patient unexpectedly became pregnant approximately six weeks after her radioactive iodine treatment. Studies have shown that with the exception of miscarriages, there is no evidence that exposure to radioiodine affects the outcome of subsequent pregnancies and offspring. Although the number of children born of mothers exposed to radioiodine is relatively small, the present data indicates that there is no reason for patients exposed to radioiodine to avoid pregnancy. The only adverse effect observed in the study series is an increased incidence of miscarriages in women exposed to therapeutic radioiodine during the year which preceded conception. The fetus would be at risk due to maternal hypothyroidism. Discussion: Radioactive iodine exposure does not appear to be associated with an increased risk of miscarriage or abnormal subsequent pregnancies. Conclusion: Pregnancies achieved after exposure to radioactive iodine treatment do not appear to be at increased risk for negative outcomes. Nevertheless, it is recommended that pregnancy be avoided for 1 year following radioactive iodine therapy to allow reproductive function to normalize.