SAT-366 - Diffuse Large B-Cell Primary Thyroid Lymphoma Arising in the Setting of Hashimoto'S Thyroiditis

Background: Primary thyroid lymphoma (PTL) is a rare thyroid cancer arising in the setting of Hashimoto’s thyroiditis and comprises less than 5% of all thyroid malignancies. Within this diagnosis, diffuse large B-cell lymphoma (DLBCL) accounts for most cases and is known to have a poorer prognosis compared with other PTL subtypes. Given its aggressive nature, it is important to promptly recognize the malignant potential associated with this chronic autoimmune condition and prevent diagnostic and treatment delays.

Case Presentation: A 56-year-old man with a 12-year history of Hashimoto’s thyroiditis and prior tobacco use was referred to the emergency department due to a rapidly enlarging neck mass. Prior outpatient workup with CT of the neck demonstrated a necrotic thyroid lobe mass, and a PET scan showed a hypermetabolic thyroid gland with a necrotic right lobe and associated cervical lymphadenopathy, suspicious for primary thyroid malignancy. On admission, the patient reported pain secondary to neck swelling but denied dysphagia, dysphonia, or difficulty breathing. Vital signs were stable on arrival, and laboratory studies were grossly unremarkable. CT of the neck showed a 5 cm mass in the right thyroid lobe with leftward deviation of the trachea and esophagus without narrowing. The patient was started on steroids for mass effect and swelling, with symptomatic improvement. He underwent fine needle aspiration of the right thyroid lobe, and the remainder of his hospital stay was uncomplicated; he was discharged home. Pathology results revealed malignant DLBCL with sclerosis and necrosis.

Discussion: This case highlights an atypical, early presentation of PTL in a male with a history of Hashimoto’s thyroiditis. This autoimmune condition, which predominantly affects women, is a well-established risk factor for PTL. PTL typically develops a few decades after Hashimoto’s thyroiditis. This case underscores the importance of maintaining a high clinical suspicion for this uncommon complication in patients with a history of Hashimoto’s, despite its short latency period, to facilitate timely diagnosis and treatment.

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