SAT545 Erythropoietic Thyroid Nodule in the Setting of Myelofibrosis

Disclosure: L.M. Vasquez: None. J.M. Bruder: None. M. Koops: None. J. Trejo: None. Background: Extramedullary hematopoiesis is frequently seen in non-osseous locations but not endocrine organs, this is a case of hematopoesis in a thyroid nodule. Clinical Case: A 79-year-old man with myelofibrosis diagnosed at age 66, CAD post CABG, atrial fibrillation on anticoagulation and HFrEF was referred to the endocrinology clinic due to enlarging left lobe thyroid nodule. He was diagnosed with a goiter at age 72 but denied compressive symptoms. He had no history of radiation to his neck or family history of thyroid cancer. On physical exam, the left thyroid lobe was visibly enlarged with slight right tracheal deviation without lymphadenopathy. TSH level was normal. Thyroid ultrasound demonstrated a 6.4 x 4.0 x 4.8 cm, complex cystic-solid, taller than wide nodule in the left lobe and a sub-centimeter cystic nodule in the right lobe. FNA showed hematopoietic elements, including maturing cells in three lineages of hematopoiesis. On repeat ultrasound 5 years later. The left nodule increased in size to 7.3 x 5.4 x 4.4 cm and highly suspicious (TR4 and TR3) by Ti-RADS criteria. Repeat FNA of the nodule showed many red blood cells with few hematopoietic cells, flow cytometry did not show any abnormal populations. No thyroid follicular cells were reported. Myelofibrosis was diagnosed by bone marrow biopsy many years prior. He had maintained a stable CBC without palpable spleen or hepatomegaly. Given this history without thyroid dysfunction or reported symptoms, surgery was not pursued. External beam radiation was a treatment option should the nodule cause symptoms. He continued to have mild anemia not requiring blood transfusions. He passed away 2 years later in hospice care after hospitalization for severe heart failure decompensation. Conclusion: Extramedullary hematopoiesis involving the thyroid is rare but has been reported(1). This type of extramedullary hematopoiesis. can be treated with surgery or low-dose radiation because of the radiosensitivity of hematopoietic tissue (2). This was a potential treatment modality if compressive symptoms arose, but they did not. This case illustrates a situation in which surgical intervention on highly suspicious nodules would not have been the optimal treatment choice. Reference: 1. Jan I., Weng M., Wang C., et al. Extramedullary hematopoiesis involving the thyroid: A rare cytologic finding in otherwise healthy patients and review of literature. Journal of the Formosan Medical Association. (2018) 117, 1108-1114. 2. Taher A, Vichinsky E, Musallam K et al., authors; Weatherall D, editor. Guidelines for the Management of Non-Transfusion Dependent Thalassaemia (NTDT) [Internet]. Nicosia (Cyprus): Thalassaemia International Federation; 2013. Chapter 11, EXTRAMEDULLARY HEMATOPOIESIS. Available from: https://www.ncbi.nlm.nih.gov/books/NBK190455/ Presentation Date: Saturday, June 17, 2023