What is the most likely treatment for a pregnant woman in her 2nd trimester (14 weeks pregnancy) with symptoms suggestive of hyperthyroidism, including tremors, palpitations, and right neck swelling?

Management of Hyperthyroidism in a Pregnant Woman at 14 Weeks

Antithyroid drugs, specifically propylthiouracil (PTU), are the most appropriate treatment for a pregnant woman at 14 weeks gestation presenting with tremors, palpitations, and right neck swelling suggestive of hyperthyroidism. 1

First-Line Treatment Approach

• Propylthiouracil (PTU) is the preferred antithyroid medication during the first trimester of pregnancy due to lower risk of congenital abnormalities compared to methimazole 1
• At 14 weeks (early second trimester), consideration should be given to switching from PTU to methimazole for the remainder of pregnancy due to the risk of PTU-associated hepatotoxicity 2
• The goal of treatment is to maintain free T4 or free thyroxine index (FTI) in the high-normal range using the lowest possible thioamide dosage 1
• Regular monitoring of thyroid function every 2-4 weeks is recommended to adjust medication dosage appropriately 1

Medication Selection Considerations

• PTU may be preferred in the first trimester as methimazole has been associated with rare teratogenic effects, including choanal atresia and aplasia cutis 3, 4
• The FDA warns that PTU can cause severe liver injury and acute liver failure, so monitoring liver function is essential 2
• Given that the patient is at 14 weeks, a transition from PTU to methimazole may be appropriate to minimize hepatotoxicity risk while avoiding first-trimester teratogenic effects 2, 3

Monitoring and Adjunctive Therapy

• Monitor free T4 or FTI every 2-4 weeks to guide dosage adjustments 1
• Beta-blockers (e.g., propranolol) can be temporarily used to manage symptoms like tremors and palpitations until thioamide therapy reduces thyroid hormone levels 1
• Check TSH level every trimester to ensure stable thyroid function 1
• Monitor for side effects of thioamides, particularly:
  • Agranulocytosis (presenting with sore throat and fever) 1
  • Hepatotoxicity (anorexia, right upper quadrant pain, jaundice) 2
  • Vasculitis (rash, hematuria, decreased urine output) 2

When to Consider Surgery (Thyroidectomy)

• Thyroidectomy should be reserved for women who do not respond to thioamide therapy 1
• If the patient develops intolerance to antithyroid drugs (such as agranulocytosis or severe hepatotoxicity), thyroidectomy may be considered 1
• If surgery is necessary, the second trimester is the preferred timing 1

Contraindications and Cautions

• Radioactive iodine (I-131) is absolutely contraindicated during pregnancy as it can cause fetal thyroid ablation 1, 5
• Inadequately treated hyperthyroidism increases risks of preeclampsia, preterm delivery, heart failure, and possibly miscarriage 1
• Fetal and neonatal risks include low birth weight and potential thyroid dysfunction 1

Special Considerations

• The patient should be warned about potential side effects of antithyroid medications and instructed to report symptoms immediately 2
• A multidisciplinary approach involving endocrinology and high-risk obstetrics is recommended 5
• The newborn's physician should be informed about maternal Graves' disease due to the risk of neonatal thyroid dysfunction 1

Remember that untreated hyperthyroidism poses greater risks to both mother and fetus than properly managed antithyroid therapy 6, 7.