An Unusual Riddle of Thyroid Swelling; Hodgkin’s Lymphoma Masquerading as Riedel’s Thyroiditis

Introduction: Thyroid swellings are one of the most common encountered endocrinological presentations however the prevalence of malignancy is about 4-6.5%. Hodgkin lymphomas usually present as neck swelling in form lymphadenopathy and Hodgkin disease affecting the thyroid gland is extremely rare (1-2.5% of all lymphomas). It usually occurs in middle age and has predilection for female gender. It can pose a diagnostic challenge with the histology of sclerosing fibrosis mimicking Riedel’s thyroiditis; another rare cause of stony hard goitre. Case History: A 39yr old female presented with rapidly enlarging painful thyroid mass. She complained of mild dysphagia but denied to have dyspnoea, dysphonia wheeze or stridor. There was no history of weight loss, B symptoms or any significant past illness. Clinically and biochemically she was euthyroid with normal TSH 0.73mU/l(0.35-3.50), Free thyroxine 13pmol/L (8-21), Free T3 3.9pmol/L (3.8-6.0). Blood count showed mild neutrophilia 8.21 (2-7x109/L). IGG subclasses 1-4 were all with normal limits. Initial Ultrasonography demonstrated 4.6 X 3.6cm U3 thyroid nodule extending retrosternally. FNA x2 was THY. Core biopsy demonstrated dense core of fibrous tissue with crushed aggregates of mature lymphoid cells and mixed neutrophils and histiocytes in keeping with fibro inflammatory process suggestive of Riedel’s thyroiditis. Patient was initiated on Prednisolone 100mg OD by the ENT surgeons after MDT discussion and patient had some symptomatic improvement in pain but no discernible reduction in size. Due to side effects from steroids she was referred to endocrinology department. Tamoxifen 20mg BD was started for symptom management. CTNCAP was organised to rule out lymphoproliferative disorder which was negative barring the known thyroid mass. She had no response to Tamoxifen either hence she underwent surgical resection. Surgical resection deemed very difficult due to mass infiltrating the strap muscles and neck vasculature hence wedge resection of the isthmus was done. Histology now revealed bands of dense fibrous tissue with admixed large lymphoid cells showing enlarged, red nucleoli. Immunohistochemistry of the large atypical lymphoid cells expressed CD30, CD15, MUM1, PAX5, CD20, CD79a and BCL6 and diagnosis was revised to Classic Hodgkin lymphoma, nodular sclerosis subtype. She was then referred to haematologist who initiated ABVD chemotherapy and her latest FDG PET scan shows complete metabolic response with significant reduction in the thyroid mass to 17mm X16 mm. Conclusion: Primary thyroid lymphoma can mimic Riedel’s and other forms of fibrosing thyroiditis. Most lymphomas arise from Hashimoto’s thyroiditis. Stony hard neck swellings are difficult to FNA and even core biopsy may not reveal the diagnosis, hence surgical resection and histological diagnosis should be sought earlier as most lymphomas respond well to chemotherapy.