What is primary thyroid lymphoma?

Updated: May 14, 2020
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Primary lymphomas of the thyroid gland represent approximately 2-5% of all thyroid malignancies. Most thyroid lymphomas are non-Hodgkin B-cell tumors. The next most common histologic type is low-grade malignant lymphoma of mucosa-associated lymphoid tissue (MALT). Hodgkin lymphoma, Burkitt cell lymphoma, and T-cell lymphoma have also been reported.

The incidence peaks in the sixth decade of life, and most diagnoses are made in patients aged 50-80 years. Women are more commonly affected than men, with a female-to-male ratio of 4:1. This tumor is highly associated with chronic lymphocytic thyroiditis (Hashimoto thyroiditis). Almost all patients with primary thyroid lymphoma have either a clinical history or histologic evidence of chronic lymphocytic thyroiditis. The risk of primary thyroid lymphoma increases 70-fold in patients with chronic lymphocytic thyroiditis compared with the general population.

The most common clinical presentation is an enlarging thyroid mass. Patients may have clinical or serologic evidence of hypothyroidism. Local extension into the aerodigestive tract or surrounding tissues may cause dysphagia, dyspnea, or symptoms of pressure in the neck. Vocal fold paralysis and hoarseness suggest involvement of the recurrent laryngeal nerve. Regional and distant lymphadenopathy is common.

Diagnosis is based on the patient's clinical presentation with a positive tissue diagnosis. FNAB may be useful for diagnosing thyroid lymphoma, but it is considered less reliable with this lesion than with other thyroid malignancies. Lymphoma may be difficult to differentiate from chronic lymphocytic thyroiditis. Surgical biopsy of the lesion is preferred for diagnosing thyroid lymphoma. Biopsy enables thorough histochemical and immunohistochemical analysis to confirm the diagnosis. Tumor cells are positive for leukocyte-common antigen and for B- or T-cell markers depending on the type of tumor.

Staging of thyroid lymphomas is important for therapeutic and prognostic purposes. Staging involves CT scanning of the brain, neck, chest, abdomen, and pelvis, as well as bone marrow biopsy. Most primary thyroid lymphomas are localized to the thyroid gland alone and, therefore, classified as stage IE (localized to an extranodal site). Involved regional lymph nodes increase the stage to IIE.

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