Solitary Extramedullary Plasmacytomas of the Thyroid in Hashimoto's Thyroiditis

Dear Editor:

Solitary extramedullary plasmacytomas (SEPs) arising in the thyroid most commonly occur in patients with a history of Hashimoto's thyroiditis (82%) (1). Although the association is not clearly understood, it is believed that the autoimmune process of Hashimoto's thyroiditis, which includes widespread lymphocyte infiltration, fibrosis, and inflammatory destruction of thyroid follicles, increases susceptibility to thyroid malignancy (2). Indeed, Hashimoto's thyroiditis has also been associated with an increased incidence of papillary carcinoma, lymphoma, and other malignancies (3). Here, we present a case of SEP of the thyroid gland associated with Hashimoto's thyroiditis.

A 45-year-old Filipino, with a history of Hashimoto's thyroiditis presented to the ENT clinic at the Sunnybrook Health Sciences Center, Toronto, with a thyroid goiter and significant dysphagia. He was hypothyroid, and on thyroid medication. A needle biopsy was consistent with thyroiditis, and he was positive for antithyroglobulin antibodies. His compressive symptoms from the goiter resulted in a positive Pemberton's sign, with dilatation of his external jugular veins bilaterally, and facial flushing upon elevation of upper limbs.

A CT scan confirmed a multilobular heterogeneous enlargement of both thyroid lobes, with extension to the anterior superior mediastinum and thoracic outlet (See Supplementary Data, available online at www.liebertpub.com/thy). There was evidence of a mass effect on the internal jugular veins and trachea, and several notably enlarged lymph nodes in levels II-b and III. Ultrasound revealed the lobes to have hypoechoic nodules surrounded by heterogeneous parenchyma. After suffering from apparent intranodular hemorrhage and worsening of his compressive symptoms, he was brought to the operating room as an urgent designation case. Dissection revealed a retrosternal goiter, with a 3-cm tracheal deviation, and esophageal compression onto the C5-7 vertebral bodies. A frozen-section analysis was consistent with a lymphoid mass with 27% polyclonal B cells. He had no complications following the total thyroidectomy, and bilateral neck dissection in levels 2, 3, 4, and 6. The patient recovered uneventfully, with a normal vocal cord function and normocalcemia.

SEPs are rare, comprising less than 5% of lymphomas (3). Although the majority of SEPs arise in the head and neck, few cases of thyroidal SEPs have been reported. SEPs of the thyroid are defined as histologically proven plasma cell tumors that are solitary, with neoplastic characteristics (poorly differentiated histology, M protein production, or monoclonal by immunohistochemistry), and a normal bone marrow (1).

SEPs are commonly present in patients in their fifth to seventh decade of life, with local compressive symptoms (50%), rapidly enlarging nodule (38%), and hoarseness (24%) (1). SEPs of the thyroid are considered rapidly enlarging, if growth is measured within three months.

Recent recommendations for the diagnosis of SEP include (i) histologically normal marrow aspirate and trephine; (ii) normal results on skeletal survey, including radiology of long bones; (iii) no anemia, hyperkalemia, or renal impairment due to plasma cell dyscrasias; and (iv) absent or low serum or urinary level of monoclonal immunoglobulin (3).

Although there has not been a standardized consensus on the best management practices for SEPs of the thyroid, SEPs occurring in other soft tissue sites of the head and neck have been treated by radiotherapy, surgery, or both. A recent study by Bachar et al. found local recurrence rates to be 12.5% in patients treated with either radiation or surgery alone. However, when tumors are located in areas in close proximity to vital structures, surgery followed by radiation was required, and had a local recurrence rate of 20% (4).

Given the excellent long-term control rates with radiation alone, radiation should be considered the primary therapy. There is no strong evidence for administration of chemotherapy in most patients with SEP; however, its utility has been suggested for tumors larger than 5 cm, that are high grade, refractory, relapsed, or for multiple myeloma (3). The largest study to date in SEP of the thyroid by Kovacs, indicated that 73% of patients were free of disease; 3% were alive with evidence of disease; and 13% had died from it at a follow-up duration of 56–73 months (1).

SEPs of the thyroid should be considered in the differential diagnosis whenever a patient with Hashimoto's thyroiditis presents with a rapidly enlarging thyroid nodule. A number of reports have recommended local surgery in combination with local radiotherapy as the primary treatment of choice, while reserving systemic chemotherapy for recurrences, multiple myeloma, and multiple extramedullary plasmacytomas (3). Progression to multiple myeloma or multiple extramedullary plasmacytoma is unknown; however, as these are the most significant problems for these patients, long-term surveillance is recommended.