61 year old female was referred for an incidental 25mm right thyroid lobe nodule on neck ultrasound while investigating for a posterior neck lipoma. She has a 3 year history of Hashimoto’s Thyroiditis (HT) and hypothyroidism on Thyroxine 50mcg replacement. Thyroid ultrasound demonstrated atypical features with fine needle aspiration (FNA) indicating a poorly amorphous lymphoid population with no colloid or thyroid component raising the possibility of thyroid lymphoma. Right thyroid lobectomy was performed with histopathology confirming follicular lymphoma Grade 1-2 arising from a background of HT. Haematology review is pending.
Primary thyroid lymphoma (PTL) is rare, accounting for ~1-2% of extranodal lymphomas with the majority of cases being diffuse large B-cell lymphoma (DLBCL) followed by mucosa-associated lymphoid tissue (MALT) lymphoma, while follicular lymphoma only accounts for ~10% of cases.1,2 It predominantly affects middle-aged women, as in our case.1,2 Patients with HT have a greater than 60-fold increase risk of developing PTL , with lag time of HT to PTL diagnosis between 18 months and 9 years.1,2,3 It is hypothesised that chronic antigenic stimulation of the lymphocytes predisposes cells to lymphomatous transformation.1,2
An enlarging goitre with background of HT should raise suspicion of PTL.4 Traditionally core-needle or surgical biopsies were performed due to difficulty in distinguishing thyroiditis from low -grade PTL.4 With advances in immune-phenotypic analysis, the accuracy of FNA has improved.4 Once PTL diagnosis is established, it is staged as per Ann Arbor Staging criteria.4 Localised and indolent disease such as MALT and follicular lymphoma are usually treated with radiotherapy.4,5 Surgery has not been shown to add any benefit to radiotherapy alone other than relief of compressive symptoms.4,5 Disseminated or aggressive disease including DLBCL, is treated with combined chemotherapy and radiotherapy.4,5 From the SEER Database, PTL over 32 years of follow-up have median overall survival of 9.3 years.6