Hyperthyroidism Flashcards
What are signs and symptoms of hyperthyroidism?
Symptoms: nervousness, heat intolerance, diaphoresis, fatigue, anxiety, emotional lability, weight loss, retraction of the eye lid, pretibial myxedema and diffuse goiter, severe nausea and excessive vomiting, diarrhea, myopathy, lymphadenopathy, and congestive heart failure which often presents in thyrotoxicosis.
Signs: tachycardia and hypertension, wide pulse pressure
How do you diagnose hyperthyroidism?
Low TSH, high free T4 or high free T3
What is Graves’ disease?
Graves disease is an autoimmune disease mediated by antibodies that activate the TSH receptor and stimulate thyroid follicular cells. It affects 3% of women of reproductive age.
How is Graves disease diagnosed?
Thyroid stimulating immunoglobulins are considered to be the antibodies specific to Graves disease, and they can be measured by bioassays or receptor assays. TSH-inhibitory immunoglobulin has also been associated with Graves disease.
What is Hashimoto’s thyroiditis and how is it diagnosed?
Hashimoto thyroiditis, also called chronic lymphocytic throiditis, is an autoimmune disease and is the most common cause of hypothyroidism in pregnancy. It is characterized by glandular destruction by autoantibodies. Antithyroid antibodies are are elevated in 50-70% of patients, particularly antithyroid peroxidase antibodies.
What are the maternal and fetal risks of hyperthyroidism in pregnancy?
preterm delivery, low birth weight, possible fetal loss, perinatal mortality, thyrotoxicosis and maternal heart failure.
Fetal hyperthyroidism: growth restriction, advanced bone age, and craniosynostosis
What is the mechanism of action of anti-thyroid medication (PTU and methimazole)?
They are Thionamides used to inhibit the iodination of thyroglobulin and thyroglobulin synthesis by competing with iodine for the enzyme peroxidase. Propylthiouracil (PTU) (but not methimazole) also inhibits the conversion of T4 to T3.
The transplacental passage of the two drugs is similar.
Methimazole may cause cutis aplasia, a scalp deformity and rarely causes choanal atresia, tracheoesophageal fistula, and facial anomalies and is preference to use after the first trimester.
PTU can cause hepatotoxicity and is preference to use in the first trimester and also with T3 based toxicity.
PTU and Methimazole dosing:
PTU is given every 8 hours at doses of 100 to 150 mg (300 to 450 mg total daily dosage) according to thyrotoxicosis severity.
PTU relative to methimazole are 10 : 1 or 15 : 1 (100 mg of PTU is equivalent to 7.5 to 10 mg of methimazole).
Usual starting doses are up to 300 mg of PTU and up to 20 mg of methimazole.
What is your DDX of low TSH in the first trimester in pregnancy?
- Pregnancy
- Subclinical hyperthyroidism
- Hyperthyroidism
What work-up do you perform when a low TSH is identified in the first trimester of pregnancy?
Consider free T4 but this may be high due to hcg stimulation
What are your goals of treatment for hyperthyroidism?
Doses of thionamides should be adjusted to keep free T4 level in the upper normal range and TSH level less than 0.5 mU/L during pregnancy to avoid hypothyroidism in the fetus. The drugs can often be stopped in late gestation.
Fetal signs of hyperthyroidism:
- growth restriction
- advanced bone age
- craniosynostosis
Why does goiter develop in cases of fetal hyperthyroidism?
Hyperthyroidism in fetuses and neonates is usually produced by transplacental passage of TSIs and activation of the fetal thyroid, occurring in 1% of offspring of patients with Graves disease.
Maternal TSI levels in excess of 300% of control values predict fetal hyperthyroidism
What is thyroid storm?
a life threatening hypermetabolic state characterized by:
- fever
- tachycardia
- altered mental status
- diaphoresis
- wide pulse pressure
What lab work changes do you expect to see in a patient with thyroid storm?
Leukocytosis
Elevated bilirubin and transaminase
Hyperglycemia
