摘要：

Primary thyroid lymphoma is a rare malignancy with certain unique predisposing factors, clinical features, and evaluation techniques. The author reports the case of a 77-year-old woman who was diagnosed with Hashimoto's thyroiditis based on a goiter, high thyroid autoantibody titers, and elevated thyroid-stimulating hormone. Fine-needle aspiration (FNA) of the prominent right lobe showed lymphocytic infiltration and she was started on levothyroxine. She subsequently developed breast cancer requiring treatment with external radiation. Ten years later, she had compression symptoms, thyroid enlargement, and a significant increase in size of the right thyroid lobe on office ultrasound. A repeat FNA revealed lymphocytic infiltration but it was nondiagnostic. The patient underwent hemithyroidectomy, which showed a large diffuse B-cell lymphoma arising within Hashimoto's thyroiditis. The case illustrates the typical risk factors for thyroid lymphoma: female gender, older age, presence of longstanding Hashimoto's disease, history of radiation exposure, and rapid clinical enlargement. It also emphasizes that FNA can be undependable and even misleading because of preexisting lymphocytic infiltration from chronic thyroiditis. An operative surgical specimen is frequently needed for proper histologic diagnosis. Clinicians should maintain a high index of suspicion for thyroid lymphoma if known predisposing features are present in a particular patient and understand the limitations of FNA biopsy in this setting.

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