Lymphoma is a cancer of the white blood cells that can be found in the bloodstream or lymph nodes. In rare cases, it arises from lymphocytes that are present within the thyroid gland, known as primary thyroid lymphoma. This type of lymphoma is distinct from lymphomatous involvement of the thyroid gland due to metastasis or direct extension. Primary thyroid lymphoma is further classified as either aggressive or indolent, depending on its severity.
It is estimated to account for 1-2% of all extraganglional lymphomas and 2-8% of all malignant thyroid tumors. It is well known that primary thyroid lymphomas often arise against the background of Hashimoto's Thyroiditis (HT). This autoimmune disorder induces reactive lymphoid proliferation, which can lead to the development of MALT (mucosa-associated lymphoid tissue) lymphoma. In turn, this can progress to aggressive lymphoma through the accumulation of abnormalities. Hypothyroidism in these patients is commonly due to HT and, infrequently, diffuse infiltration of the thyroid gland by lymphoma. Unlike most thyroid cancers that don't cause symptoms, thyroid lymphomas tend to grow rapidly and cause compressive symptoms such as difficulty swallowing, getting stuck food or pills when swallowing, and pressure or difficulty breathing when lying flat.
It is essential to differentiate between anaplastic thyroid cancer and thyroid lymphoma because the treatment and prognosis are very different. It is important to consider the diagnosis of primary thyroid lymphoma in patients with an enlarged neck mass and a history of HT. The initial physician should have a high degree of suspicion and involve an otolaryngologist and pathologist to establish a diagnosis with a thick biopsy of the thyroid. The surgical intervention did not appear to be associated with an adverse outcome in patients with thyroid Hodgkin lymphoma, similar to patients with non-Hodgkin's thyroid lymphoma. The incidence and prevalence of primary thyroid lymphoma are higher in areas with higher rates of HT. Therefore, it is important for healthcare professionals to be aware of this association and consider it when diagnosing patients with HT.
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