Introduction: Primary thyroid lymphoma (PTL) is a rare cause of malignancy, accounting for <5% of thyroid malignancies and < 2% of extra-nodal lymphomas. Most thyroid lymphomas are non-Hodgkins lymphomas of B-cell origin. Patients with Hashimotos thyroiditis are at greater risk for developing PTL. Early diagnosis is important as treatment and prognosis of PTL depend upon the histology and stage of the tumour at diagnosis. We report a rare case of primary thyroid lymphoma in a patient presenting with a rapidly enlarging thyroid goitre highly suspicious of anaplastic thyroid carcinoma posing as a diagnostic histological challenge due underlying Hashimotos thyroiditis which was unmasked after a short course of oral steroids.
Case report: A 51 years old female was referred by GP with increasing painless swelling over the right side of neck over a period of 3 weeks. She did not have any difficulty in swallowing or breathing. There was no history of any weight loss or night sweats. Her TSH was 9.57 mIU/L with a normal free T3, T4 and positive thyroid peroxidase antibody suggestive of subclinical hypothyroidism secondary to Hashimotos thyroiditis. The scan showed a large mass on the right side of the thyroid gland measuring 4.8 × 4.6 × 3.7 cm, encasing the common carotid artery with complete compression and thrombosis of the internal jugular vein. There were multiple lymph nodes on the right side of neck. Initial imaging was highly suspicious of anaplastic thyroid cancer which carries a poor prognosis. She was referred to our thyroid surgeon and had a fine needle aspiration which unexpectedly only showed inflammatory/reactive picture with no clear signs of malignancy. She was given oral steroids for 4 days, which decreased the size of the neck swelling followed by a core biopsy. The resultant histology showed clearance of the inflammatory picture whilst unraveling histological features of a high grade lymphoma. A diagnosis of B cell lymphoma was confirmed by the Haematologist. From a haematological perspective, giving steroids prior to diagnostic biopsy for suspected lymphoma is strongly discouraged as steroids can partially treat high-grade lymphomas, induce necrosis and render the biopsy uninterpretable.
Conclusion: This case highlights the unexpected paradoxical role of steroids in unmasking the histopathological diagnostic dilemma of PTL which carries a more favourable prognosis compared to anaplastic thyroid carcinoma whilst shrinking the mass.