A rare case of chronic lymphocytic leukemia/small lymphocytic lymphoma presenting in the thyroid gland.

Background: Lymphoma involving the thyroid gland is rare. Diffuse large B-cell lymphoma and mucosa-associated lymphoid tissue lymphoma are the two most common histologic subtypes of primary thyroid lymphoma. Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) presenting initially as a thyroid abnormality is extremely rare, with very few reported cases in the literature.

Summary: We report a case of a patient with a long history of Hashimoto's thyroiditis and goiter who presented with a recent enlargement of her thyroid gland. The sonographic finding of a distinct thyroid nodule in the heterogeneous background of chronic lymphocytic thyroiditis led to the performance of a fine-needle aspiration biopsy and flow cytometry, with a high index of suspicion for thyroid lymphoma. Subsequent surgical removal of the thyroid gland, prompted by the patient's history of head and neck radiation, confirmed the diagnosis of CLL/SLL. The patient's systemic illness was recognized only after the management of her thyroid disease. Although thyroiditis has long been associated with lymphoma arising in the thyroid gland, CLL/SLL involving the thyroid has not been linked to chronic lymphocytic thyroiditis. Therefore, the patient also had coexisting thyroiditis.

Conclusions: Due to the rarity of thyroid lymphomas, our experience in the detection and management of this disease is limited. Primary thyroid lymphoma should be suspected in a patient with a history of chronic lymphocytic thyroiditis presenting with a rapidly enlarging neck mass. The initial diagnostic method for thyroid lymphoma should consist of a fine-needle aspiration biopsy with the use of ancillary techniques such as flow cytometry and immunohistochemistry for improved diagnostic accuracy. Although controversial, the treatment of thyroid lymphoma is typically guided by the histologic subtype and extent of disease. CLL/SLL is one of the rarest subtypes of lymphoma that can involve the thyroid gland. Diagnosis of this entity is difficult, particularly before the recognition of systemic involvement, requiring the expertise of a multidisciplinary team for early detection and optimal management.