PSAT239 Pregnant Patient With a History of Methimazole-Induced Agranulocytosis Presenting With Hyperthyroidism: A Case Report

BACKGROUND: Pregnancy has a profound impact on the thyroid gland and its function. Severe thyrotoxicosis can lead to many complications and endanger the mother or fetus. Antithyroid drug (ATD), at its lowest possible dose, should be given. However, one of the complications of treatment include agranulocytosis which is a rare but serious allergic event with a prevalence of 0.1 to 0.5 percent. Thus, alternative treatment should be prescribed because a cross-reaction between ATDs was observed in 15.2% of patients in a study. Insufficient data is available regarding the use of these medications in pregnant patients with history of drug-induced adverse reactions. There are other feasible alternative treatments but are contraindicated in pregnancy. CASE: We report a 29-year old patient gravida 5 para 4 at 10 weeks age of gestation at the time of consult presenting with palpitations. She is a known case of Graves’ disease for 7 years and maintained on Methimazole. She was admitted a year prior consult as a case of impending thyroid storm; Methimazole-induced agranulocytosis. Initially, maintained on Lithium but shifted back to Methimazole without a physician's advice and later on, discontinued the medication upon knowledge of pregnancy. She presented on her first trimester of pregnancy with palpitations and elevated free thyroxine (T4) at 71.29 pM (normal range: 11-24 pM). She was started on Propylthiouracil 50 mg/tablet 1 tablet three times a day. On her second trimester, no reported symptoms of hyperthyroidism and/or agranulocytosis such as fever or sore throat. Thyroidectomy was offered at this time explaining the risks and benefits but she strongly refused. Free T4 was then maintained at a value slightly above the upper normal limit. Propylthiouracil was also shifted to Methimazole 5 mg/tablet 1 tablet once daily and revised to 1 tablet every other day on the third trimester of pregnancy. Delivery was uneventful and the newborn was evaluated by a pediatrician with unremarkable findings. Four weeks postpartum, no noted symptoms of hyperthyroidism and/or agranulocytosis. Free T4 was noted within the normal range at 18.84 pM. Alternative treatment was offered due to the risk of ATD-induced agranulocytosis. CONCLUSION: Hyperthyroidism in pregnancy is associated with a variety of complications for the mother and fetus. Three effective treatment options include ATD, thyroidectomy or RAI therapy. But, not all are relatively safe for pregnancy. In initiating ATD, cross-reaction between medications should be considered especially for patients with history of adverse reaction, such as agranulocytosis, which can be life-threatening. However, there are limited studies in the management of this specific case. Treating physician and patient should discuss each of the options, including the benefits, drawbacks and side effects. Keywords: Hyperthyroidism, Graves’ disease, Pregnancy, Agranulocytosis Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.