Diseases of the Thyroid Flashcards
Why does Amiodarone use decrease iodine uptake in radioiodine uptake (RAIU) scans?
Amiodarone is iodine-rich but also blocks peripheral deiodination of revers T3 and T4, resulting in increased reverse T3 and T4 and a decreased T3. It can cause a patient to be hyperthyroid (due to the iodine) or hypothyroid (due to too much iodine and the peripheral deiodination). Either way, RAIU is low because the thyroid is already saturated with iodine prior to the radioiodine dose.
Compare/contrast the radioiodine uptake scan with the thyroid scan.
RAIU uses radioactive iodine to measure the percentage taken up by the thyroid. The thyroid scan uses technetium to create a picture of how the isotopes localize within the thyroid. (RAIU produces a number, thyroid scan produces a picture).
What are the expected lab findings in a patient with acquired tertiary hypothyroidism (hypothalamus-derived)?
Low TSH and low or inappropriately normal free T4
Fill in Table 15-5 for how to interpret thyroid function tests.
What should one consider if the total T4 level is outside of the normal range?
First, ensure that the thyroxine-binding globulin levels are within normal limits. If TBG is outside the normal range, total T4 will be as well, and is not clinically significant.
What is suppurative thyroiditis and where does it most commonly occur?
It is a bacterial infection of the thyroid gland and typically affects the left lobe of the thyroid.
What factors are concerning about the presence of a solitary thyroid nodule in a child?
A solitary thyroid nodule in the first 20 years of life is much more likely to be malignant than in an older person, and about 26% of thyroid nodules in children are malignant.
What prophylactic procedure is recommended for certain mutations in MEN 2A and 2B?
Certain oncogenes in MEN 2A require thyroidectomy by 5 years of age and by 6 months of age with certain oncogenes in MEN 2B.
What happens to growth in a child with acquired hypothyroidism?
Growth failure is a hallmark of the disease. In most cases growth practically ceases and patients will have a weight for age that is proportionately greater than height for age.
Which thyroid hormone should be followed in patients with primary hypothyroidism?
TSH
If a patient with a thyroid nodule undergoes a complete thyroidectomy, what is a reliable tumor marker that should be followed to monitor for recurrence?
Thyroglobulin level
What should be the first step if an infant has a positive newborn screen for congenital hypothyroidism?
Send a serum TSH and free T4 to confirm the diagnosis or to diagnose congenital TBG deficiency.
What is the recommended treatment for myxedema coma?
Thyroid hormone supplementation, stress-dose glucocorticoids (until adrenal insufficiency is ruled out), and supportive care.
What correlates with the risk of neonatal Graves’ in a baby born to a mother with Graves disease?
The maternal level of TSI (TSH receptor-stimulating antibody) determines the infant’s risk for developing neonatal Graves disease as well as its’ severity. Maternal thyroid function tests have no predictive value for the infant.
What characterizes APS (autoimmune polyglandular syndrome) Type 2?
Autoimmune thyroiditis accompanied by diabetes mellitus and adrenal cortical insufficiency. It usually presents in young adults.
What is the most likely cause of elevated TSH in a patient on levothyroxine?
This value would be indicative of noncompliance until proven otherwise.
What symptoms should patients be instructed to go to the ED for if they are undergoing medical management for Graves disease? Why?
If patients develop sore throat and mouth ulcers while taking either methimazole or PTU for treatment of Graves disease they should present to the ED for evaluation of possible agranulocytosis, which requires immediate attention.
What disease should be considered if a patient is found to have circulating antithyroglobulin and antithyroperoxidase antibodies?
Most patients with Hashimoto have these antibodies circulating. However, they can also be found in people with Grave’s or in normal individuals.
Which endocrine disease is characterized by autoimmune thyroiditis accompanied by diabetes mellitus and adrenal cortical insufficiency?
APS (autoimmune polyglandular syndrome)Type 2 (AKA Schmidt syndrome)
What should be used to treat infants and children with congenital hypothyroidism (drug, dose, and formulation)?
Levothyroxine; 10-15 µg/kg/day for infants, 4 µg/kg/day for older children (100 µg/m²/day at all ages); do not give liquid formulations, as there aren’t stable liquid formulations consistently available in the U.S. market.
How does Graves’ present in childhood?
Muscle weakness, anxiety, palpitations, increased appetite, weight changes (mostly weight loss, but some have weight gain), behavior problems, declining school performance, and decreased exercise tolerance. Patients frequently have cardiac signs/symptoms (cardiomegaly, widened pulse pressure, tachycardia, HTN, and gallop rhythms). 50% of patients have a thyroid bruit on exam. Tremor, excessive perspiration, and rapid tendon reflex relaxation times are also possible. Some may have goiter. In menarcheal girls, anovulatory cycles are common and they can develop oligomenorrhea or secondary amenorrhea.
What are the common presenting symptoms for neonatal Graves disease?
Irritability, flushing, tachycardia, HTN, thyroid enlargement, and exophthalmos. Cardiac arrhythmias can occur with severe disease.
What symptoms are typically associated with myxedema coma?
Diminished mental status, hypothermia, hypotension, bradycardia, hypoglycemia, and hyponatremia.
Describe the clinical and laboratory presentation of neonates with congenital hypothyroidism at birth.
Most infants are asymptomatic at birth because of transplacental passage of maternal thyroxine (T4). However, vertical transmission of T4 provides only 33% of normal levels so neonatal screening will still reveal a high TSH and a low T4.
Which of T3 or T4 is the active thyroid hormone and which is the prohormone?
T3 is the active hormone and T4 is the prohormone.
What is the typical course for patients diagnosed with medullary and undifferentiated carcinomas?
These carcinomas have high mortality rates and require radical surgery with radiation or chemotherapy.
What procedure should be performed in patients with autoimmune thyroiditis who have persistent thyroid nodules despite appropriate therapy?
Fine needle aspiration should be performed to biopsy the prominent nodule since thyroid cancer can develop in these patients.
Which thyroid hormone should be followed in patients with secondary or tertiary hypothyroidism?
Free T4
What are the expected lab findings in a patient with acquired primary hypothyroidism?
High TSH and low free T4
Know the drugs and conditions that affect Thyroid function.
What are some severe (but rare) side effects of medical management for Graves disease?
Agranulocytosis, lupus-like syndrome, ANCA-positive vasculitis (with PTU), drug-induced fever, hepatitis, nephritis, and splenomegaly.
What is “thyroid storm” and how can it be prevented?
It’s a life-threatening hypermetabolic state which presents as tachycardia, HTN, agitation, vomiting, and diarrhea caused by a massive leakage of thyroid hormone into the circulation as a result of hyperthyroid states such as Graves disease. It can be prevented by administering β-blockers until the hyperthyroid state is controlled, and before any planned surgical interference with the thyroid in hyperthyroid individuals.
What laboratory tests should be performed if Graves disease is suspected?
TSH, free T4, free T3 should be the initial tests. Once hyperthyroidism is confirmed, TSI (TSH receptor-stimulating antibody) should be measured to confirm Graves’ as the etiology. Antithyroperoxidase and antithyroglobulin antibody levels should also be sent.
What are two possible complications from thyroidectomy for Graves disease?
Post-operative hypoparathyroidism and recurrent laryngeal nerve damage.
What are the expected lab findings in a patient with acquired secondary hypothyroidism (pituitary-derived)?
Low TSH and low or inappropriately normal free T4
What are the two drug options for medical management of Graves disease in children, and what is their mechanism of action?
Propylthiouracil (PTU) and methimazole, which both block synthesis of thyroid hormones.
Draw the Hypothalamic-Pituitary-Thyroid axis.
What is the typical length of treatment and efficacy of medical management for Graves disease in children?
Medical management typically requires 2-5 years of daily therapy and frequent physician visits. About 60-70% of patients have complete remission with medical management alone.
What is euthyroid sick syndrome?
AKA low T3 syndrome. It occurs in critically ill patients and shows low total and free T3, normal or low total T4; low, normal, or high free T4, and a normal TSH. It should resolve with treatment of the primary underlying illness.
What is the treatment for Graves disease?
β-blockers should be used to control the toxic effects of circulating thyroid hormones until the thyroid can be “turned off”. Increased production of thyroid hormones should be stopped in one of three ways: ablation of the thyroid with radioactive iodine, surgical thyroidectomy, and blocking thyroid hormone biosynthesis with drugs.
What is the mortality rate for neonatal Graves disease?
Death rates approach 25% due to high-output cardiac failure.
What clinical states result in a low total T4 measurement due to a decrease in thyroid binding globulin (TBG)?
Androgens, glucocorticoids, nephrotic syndrome, and inherited TBG deficiency.
Hashimoto thyroiditis occurs with increased frequency in patients with which (4) disorders?
Type 1 DM, Trisome 21, Turner syndrome, and Klinefelter syndrome.
