Module 22

Question 1

What is the major screening test for thyroid disease, and what are its advantages over other tests?

Answer 1

• In the past the screening test was T4 (thyroxin) levels; however, there are many conditions, especially chronic disease, in which the T4 is low, but the patient is euthyroid (have normal thyroid gland function)
  
  • A better screening test is the TSH (thyroid stimulating hormone). Thyroxin provides feedback inhibition of TSH production. Therefore, with some exceptions, if the TSH is low the patient is likely hyperthyroid, and if high, the patient is likely hypothyroid.

Question 2

What considerations are involved in the treatment of hyperthyroidism during pregnancy?

Answer 2

• The fetus is dependent on maternal thyroid hormone during the first trimester. Hyperthyroidism is associated with significant morbidity including preeclampsia, congestive heart failure, preterm labor, and small for gestational age babies.
  
  • Outside of pregnancy the most common treatment for hyperthyroidism is radioactive iodine, but that is contraindicated in pregnancy. The usual treatment in pregnancy is propylthiouracil or methimazole, both of which are associated with a significant risk of serious adverse reactions. Specifically, propylthiouracil is associated with idiosyncratic liver failure in the mother (methimazole less so) and methimazole is associated with a higher risk of birth defects. These drugs cross the placenta; therefore, it is essential that the mother’s thyroid status be kept within a normal range so that the fetus does not become hypothyroid, a condition that is associated with severe mental retardation (cretinism).

Question 3

Directions on OTC products containing decongestants indicate that patients with thyroid disease should consult their physician or pharmacist before using these products. What is the basis for this warning, and try to find the evidence to support it

Answer 3

• Decongestants usually contain an adrenergic agent such as phenylephrine. Hyperthyroidism is commonly associated with atrial fibrillation and other tachyarrhythmias. In theory the adrenergic agent could increase the risk of arrhythmias, although there is no good data to confirm this hypothesis