MON-435 Hashimoto Thyroiditis and Goiter: Never Cease Follow-Up

Background Hashimoto thyroiditis (HT) is the most common cause of hypothyroidism in iodine-sufficient areas. Its incidence is estimated to be 3.5 per 1000 per year in women and 0.8 per 1000 per year in men (3). Primary thyroid lymphoma (PTL) is a rare complication of HT, but often forgotten. Regular follow-up and high clinical suspicion is needed to diagnose this complication early. We present a patient who developed PTL as a complication of HT after 10 years of diagnosis of HT and goiter. Clinical case A 70-year-old male with history of hypertension and obstructive sleep apnea followed up in the endocrine clinic for the last 10 years for Hashimoto thyroiditis and stable goiter presented with a sudden enlargement of right neck mass. In 2008 he was incidentally diagnosed with HT. In 2010 the patient returned with a neck swelling and further investigation revealed a cold nodule in the right lobe. The patient underwent aspiration biopsy with repeat finding of HT, and was followed up yearly with thyroid ultrasound and TSH. In 2014 due to concern in the echotexture of thyroid on ultrasound, he had a biopsy of the right thyroid nodule with findings again consistent with HT. No significant changes were noted on yearly follow-up ultrasound until March 2019. He presented 5 months later with a large mass on the right side of his neck. Ultrasound showed enlarged and confluent lymph nodes anterior to the enlarged right thyroid gland. Further CT evaluation showed a large right neck mass measuring 5.2 x 7.5 x 12 cm extending from the right thyroid lobe to the level of C1. The mass crossed the midline posteriorly. Fine needle aspiration was positive for malignant cells. A core biopsy confirmed diffuse large B-cell lymphoma. The patient had tests for staging, including bone marrow biopsy, and was found to be stage II E diffuse large B-cell lymphoma involving the thyroid. Subsequently, the patient was started on chemotherapy with RCHOP(Rituximab, Cyclophosphamide,Doxorubicin,Vincristine,Prednisolone). Conclusion Although Primary thyroid lymphoma (PTL) is a rare condition, it should always be considered in the differential diagnosis of a rapidly growing goiter or thyroid nodule. Its incidence is 2 per million, with nearly all cases the non-Hodgkin’s type. PTL accounts for only 0.5–5% of all thyroid malignancies and 1% to 7% of all extranodal lymphomas. The prevalence of Hashimoto thyroiditis in patients with PTL is highly variable, but patients with HT have a 40- to 80-fold increased risk of developing PTL. A rapidly enlarging neck mass with or without compressive symptoms is the common presentation of PTL. Most common histotype is diffuse large B cell lymphoma which accounts for 50% to 70% of cases. High clinical suspicion and awareness among physicians is needed to diagnose PTL early. The main treatment is chemotherapy. Surgical interventions are needed to relieve pressure symptoms. The prognosis of PTL is generally excellent.