Mucosa-associated lymphoid tissue lymphoma (MALT lymphoma) in the thyroid mimicking a painless subacute (De Quervain's) thyroiditis on presentation, fine needle aspiration and cytology, and ultrasound findings: A rare case report

INTRODUCTION: We report a rare case of mucosa-associated lymphoid tissue lymphoma (MALT lymphoma) in the thyroid mimicking painless subacute (De Quervain's) thyroiditis. PRESENTATION OF CASE: Patient with history of hypothyroidism presented with huge non-tender goiter, compression symptoms and choking, no lymphadenopathy. Ultrasound (US) showed large thyroid lobes. There was a small hypoechoic nodule, and nonspecific lymphadenopathy. Fine needle aspiration/cytology (FNAC) of right thyroid nodule showed scant follicular cells, abundant polymorphic lympocytes, epithelioid histiocytes, and tingible body macrophages, suggestive of De Quervain's (granulomatous) thyroiditis. Total thyroidectomy was decided due to compression symptoms and huge goiter. DISCUSSION: Intraoperative, thyroid was huge with no adhesions to the strap muscles/trachea. Total thyroidectomy with lymph node biopsy was undertaken. There were no complications. Postoperatively, the patient's condition was stable, breathing normally, and neck wound was clean. PTH was 11 pg/mL and calcium was 2.16 mmol/L, suggesting impending transient hypocalcemia. Histopathology showed lymphoepithelial lesions as clusters of lymphocytes within the thyroid follicles epithelium (MALT Balls). Immunohistochemical staining showed that the neoplastic lymphocytes were B cells and stained positive with B-cell markers CD20 and PAX5, but were negative for Cyclin D1 and for T cell markers CD3, CD5 and CD43. The patient was discussed at the lymphoma MDT meeting and the decision was to start the patient on radiotherapy which the patient received. CONCLUSION: Thyroid MALT lymphoma can mimic painless subacute thyroiditis. The triad of a large swelling of non-tender goiter with compression symptoms during a short period; FNAC findings suggestive of thyroiditis; and US showing enlarged thyroid lobes might cause confusion to the unsuspecting practitioner. Histopathology after excision provides definitive diagnosis.