A Rare Case of Classical Hodgkin Lymphoma of the Thyroid Gland

Background: Hodgkin lymphoma (HL) classically occurs in the lymph nodes and only in about 5% of cases occurs in extra-nodal sites. Primary thyroid lymphomas, most of which are non-Hodgkin lymphomas, comprise less than 5% of all thyroid malignancies. Only a few cases of HL of the thyroid have been reported in the literature, and in most of these cases, fine-needle aspiration biopsy (FNAB) was unreliable for diagnosis. We present a case of classical Hodgkin lymphoma of the thyroid that was falsely negative from both FNAB and core needle biopsy specimens and was diagnosed after surgery. Clinical Case: A 51-year-old female was seen for a rapidly enlarging neck mass associated with progressive dyspnea and dysphagia. Despite being a telemedicine visit due to the COVID-19 pandemic, significant enlargement and deformity of the neck were startling. The patient was clinically and biochemically euthyroid with a TSH of 2.49 mIU/L (0.5-5.0 mIU/L) and normal FT4. She denied a personal or family history of thyroid disease and neck irradiation. Thyroid ultrasound revealed a 5.3 cm hypoechoic, wider than tall nodule with smooth margins in the left lobe, and a 1.9 cm hypoechoic and taller than wide nodule in the right lobe of the thyroid. A CT scan of the neck also revealed a 1.2 cm lymph node in the left lateral aspect of the thyroid. FNAB of the nodules showed Hurthle cells in a background of crushed lymphocytes with occasional large atypical lymphoid cells. Flow cytometry performed on a repeat FNAB specimen revealed no evidence of lymphoma. A repeat CT scan of the neck performed 2 weeks later due to worsening symptoms demonstrated middle mediastinal lymphadenopathy and a large 8x4.7x4.7 cm mass contiguous with the thyroid with a 3.8 cm cystic collection within. The patient was scheduled for an oncology consultation due to the high likelihood of lymphoma but was admitted to another institution with symptoms. She underwent a thyroid core biopsy and flow cytometry, which again failed to reveal her diagnosis. She then underwent left partial thyroidectomy, and pathology demonstrated infiltrates of small lymphocytes with histiocytes, interspersed with clusters of large, irregular, multilobate cells consistent with Reed-Sternberg cells. She was diagnosed with nodular sclerosing variant of classical HL. Chemotherapy was instituted with rapid improvement in symptoms. Clinical Lesson: Primary HL of the thyroid is extremely rare and most often presents as a rapidly enlarging neck mass with or without compressive symptoms. Diagnosis with FNAB is challenging and can be misinterpreted as lymphocytic thyroiditis. In our patient, flow cytometry was performed twice and was falsely negative. The treatment of HL differs entirely from that of other primary thyroid cancers and thyroiditis. Hence, in patients presenting with classic symptoms, a high index of suspicion is needed to make an accurate and prompt diagnosis of HL.