New-Onset Graves' Disease in the Postpartum Period Initially Suspected to Represent Postpartum Thyroiditis.

Postpartum thyroid dysfunction is usually attributed to postpartum thyroiditis (PPT), a self-limited autoimmune condition. Graves' disease (GD) can also develop during the postpartum period, and the two conditions often present with overlapping features. We describe the case of a 37-year-old woman who developed severe anterior neck pain and abnormal thyroid function nine months postpartum, after she stopped breastfeeding. She was initially thought to have PPT, but serial testing showed steadily declining thyroid-stimulating immunoglobulin (TSI) and thyroid-stimulating hormone (TSH) receptor antibody (TRAb) titers, along with increased thyroid vascularity on Doppler ultrasound. These findings ultimately pointed to GD. This report illustrates the importance of longitudinal follow-up and antibody testing when postpartum thyroid dysfunction does not resolve as expected.