SAT-355 Thyrotoxicosis Associated with Leukopenia in Graves' Disease: A Case Report and Review of Medical Management

Abstract Disclosure: C. Makhija: None. M. Bhalla: None. S.S. Thangwaritorn: None. Leukopenia is characterized by a low white blood cell count (WBC) and, is an uncommon manifestation of hyperthyroidism associated with Graves’ disease, affecting approximately 10% of patients. The dilemma arises in choosing antithyroid drugs for treatment, considering their rare adverse effect of agranulocytosis. We present the case of a 35-year-old female hospitalized for sinus tachycardia, leukopenia, and anemia, and diagnosed with new-onset hyperthyroidism. Blood work at the hospital revealed elevated thyroid stimulating immunoglobulin of 2.72 IU/L (TSI range 0.54 IU/L or less), TSH of <0.001 (normal 0.4 - 4mlU/L), elevated free T3 at 7.9 pg/mL (normal 1.3 - 4.5pg/mL), and elevated free T4 at 3.36 ng/dL (normal 0.8 - 1.8 ng/dL), accompanied by low white blood cell of 2.9 K/mm³ (normal 4500-11,000/mm³), absolute neutrophil count 1,768/µL (normal 1,500 - 7,800/µL) and low hemoglobin of 7.6 gm/dL (normal female 12.1 -15.1 gm/dL). She was discharged with β-blockers and due to antithyroid drug contraindication, she was advised to pursue thyroidectomy. The patient desired medical management and was treated with low-dose methimazole at the endocrine outpatient visit with us. Hematology evaluation ruled out alternative causes of leukopenia. Gradual improvement ensued with methimazole therapy, improving thyroid hormone levels, and normalization of white blood cell count, and hemoglobin. This case challenges the perception of mild-moderate leukopenia as an absolute antithyroid drug contraindication, highlighting the potential for treating hyperthyroidism due to Graves’ disease with antithyroid agent to normalize white blood cell counts. Awareness of this rare complication and consideration of antithyroid drugs in selected cases can offer a viable therapeutic option, providing valuable insights for clinicians managing hyperthyroidism complicated by leukopenia. Presentation: Saturday, July 12, 2025