Introduction: Preeclampsia is a complication of pregnancy defined by new onset hypertension after 20 weeks with proteinuria or new onset thrombocytopenia, renal or liver dysfunction, pulmonary edema or cerebral/visual symptoms. Hyperthyroidism in pregnancy is usually due to Graves’ disease, and if poorly controlled can increase the risk of preeclampsia and thyroid storm. In this case report we present a case of preeclampsia with impending thyroid storm treated successfully with medical therapy, delivery, and plasmapheresis. Case Description: A 40-year-old female who is 31 6/7 weeks pregnant presents with cough and dyspnea. She has no known thyroid disease. Her systolic blood pressure at presentation is >160 mmHg. She is diagnosed with preeclampsia based on elevated spot protein/creatinine ratio (1.4 g/g) and persistent hypertension. A brain natriuretic peptide is elevated to 847 (reference range 4 (non-pregnancy reference range 0.70-1.48 ng/dL). She is started on therapy for impending thyroid storm, including maximum doses of propranolol, propylthiouracil, hydrocortisone and saturated solution of potassium iodide. Her thyroid stimulating immunoglobulin is > 500 (reference range 40 (reference range
