A Rare Case of Primary Thyroid Lymphoma.

Primary thyroid lymphomas (PTL) are a unique malignancy that arises from within the thyroid gland and is not typically considered in the differential diagnosis of thyroid cancers. PTL is strongly associated with underlying autoimmune thyroiditis; despite this association, there are no screening guidelines. Management of PTL involves chemotherapy, contrasting with the surgical and radioactive iodine therapies employed in differentiated thyroid cancers. We report a case of a 68-year-old male with a history of hypothyroidism and multiple comorbidities who presented with a rapidly enlarging, painless goiter, dysphagia, and symptoms of hypothyroidism, including fatigue and constipation. Laboratory evaluation revealed severe hypothyroidism and marked non-PTH-mediated hypercalcemia with associated acute renal failure. Imaging of the neck identified a large circumferential mass extending below the clavicles. Ultrasound-guided biopsy confirmed diffuse large B-cell lymphoma (DLBCL). The patient was treated initially for myxedema and hypercalcemia and subsequently initiated on R-CHOP (Rituximab, Cyclophosphamide, Doxorubicin, Vincristine, and Prednisone) chemotherapy for stage IIE diffuse large B-cell lymphoma. This case highlights an uncommon presentation of symptoms with confounding hypothyroidism. We also note that this is an uncommon malignancy in males. The case vignette emphasizes the importance of distinguishing PTL from other thyroid malignancies, given differences in prognosis and treatment. PTL is a rare but clinically significant malignancy requiring prompt recognition and tailored treatment.