Abstract #1384628: An Incidental Thyroid Lesion on FDG-PET Scan in a Patient with Long History of Hypothyroidism and Radiation Exposure

Abstract

An 81-year-old woman with history of lung cancer and hypothyroidism with an incidental thyroid lesion on (FDG)-positron emission tomography (PET) scan is subsequently diagnosed with primary thyroid lymphoma (PTL) using flow cytometry. An 81-year-old woman with a history of lung cancer and hypothyroidism presented to the endocrinology office for evaluation of a thyroid lesion. Primary hypothyroidism was diagnosed 30 years prior to presentation and was controlled with levothyroxine 88 mcg daily. Lung cancer was diagnosed 8 years prior, and treated with radiation therapy. Patient had an FDG-PET scan obtained for the evaluation of lung nodules, and a hypermetabolic focus was noted in the left thyroid region with a max SUV of 18. On thyroid ultrasound, the left thyroid lobe appeared heterogenous with solid nodular areas. The physical exam revealed a smooth but firm thyroid gland, without cervical lymphadenopathy. Laboratory workup showed thyroid stimulating hormone and free thyroxine in the normal range. Microsomal antibody was 4.2 IU/mL (< 5.6 IU/mL), and thyroglobulin antibody was 356.4 IU/mL (< 14.4 IU/mL). Fine needle aspiration (FNA) biopsy showed a polymorphous lymphoid sample. Given the high SUV on PET-scan and longstanding history of Hashimoto’s thyroiditis, repeat FNA biopsy with flow cytometry was subsequently performed and showed a lymphoid population consistent with a non-Hodgkin lymphoma (NHL). The patient was referred to oncology and diagnosed with indolent NHL. Further staging revealed interval growth in lung nodules, with biopsy showing recurrence of adenocarcinoma, but no other metastatic disease. The patient underwent radiation therapy for both her lung adenocarcinoma and primary thyroid lymphoma (PTL). Primary thyroid lymphoma accounts for less than 5% of thyroid cancers. It presents with a female predominance in the 7th decade of life, with Hashimoto’s thyroiditis as the main risk factor. Patients may present with an enlarging neck mass, with or without compressive symptoms, and cervical lymphadenopathy. Diagnosis of PTL can be made through FNA biopsy, core biopsy, or open surgical biopsy. It is important to note that because these lesions have few pathognomonic features, diagnosis with FNA biopsy alone can be difficult, and sensitivity is increased to 97% with the use of flow cytometry, as was demonstrated in our case. Treatment is with radiation therapy or combined chemoradiotherapy. Surgery has a role limited to the management of airway compromise, as surgical resection has not proven to improve overall survival. This case highlights the utility of including flow cytometry with FNA sample when diagnosing PTL.