MON-386 Subacute Thyroiditis Simulating Thyroid Malignancy: A Case Report

Abstract Disclosure: M.K. Uy: None. C.C. Liu: None. Subacute thyroiditis occurs most often in middle-aged women and has been associated with viral infection. A 37-year-old female presented with anterior neck pain resolving after a course of corticosteroids and anti-inflammatory agents. However, workup showed thyroid nodules suspicious for malignancy prompting surgical intervention. The histopathological diagnosis revealed subacute thyroiditis with further investigation unmasking pulmonary tuberculosis. A 37-year-old female presented with sudden onset anterior neck pain with a slightly enlarged thyroid gland. This was not accompanied by fever, cough, hoarseness, dysphagia. No previous upper respiratory tract infection was elicited. She initially sought consult with a surgeon and was prescribed with an antibiotic for 7 days which prompted no relief. Subsequently, she had a consult with an endocrinologist with the following results: elevated FT3 8.27 pmol/L (N: 2.80-7.10 pmol/L), elevated FT4 31.10 pmol/L (N: 12-22 pmol/L) and a low TSH 0.019 uIU/mL (N: 0.27-4.2 uIU/mL). Thyroid scintigraphy and uptake study revealed decreased blood flow to the thyroid gland and reduced tracer uptake noted in the superior portion of the right lobe and in the supero-anterior portion of the left lobe. Interpretation was a non-hyperactive thyroid gland with cold nodules in both lobes, thyroiditis not excluded. Neck ultrasound showed an enlarged right thyroid lobe measuring 3.6x1.6x1.9cm with 3 nodules seen bilaterally (right upper to lower nodule 2.6x1.6x1.3cms TIRADS 5, left upper nodule 0.7x0.7x0.4cms TIRADS 4, and left mid to lower nodule 1.9x1.4x0.8cms TIRADS 5). Chest x-ray was normal. She was then managed with prednisone and celecoxib for 2 weeks resulting in clinical improvement. However, due to the malignant characteristics of the nodule, biopsy of the thyroid nodules was proposed but the patient opted to undergo immediate surgery. The patient successfully underwent total thyroidectomy with both lobes and isthmus sent for examination. The histopathology report revealed moderate inflammation with granuloma containing multinucleated giant cells and epithelioid histiocytes without caseation necrosis. The diagnosis was subacute thyroiditis hence, malignancy was ruled out. This led to further investigations where a chest computed tomography scan showed minimal fibro-hazed density in the inferior lingula, to consider pulmonary tuberculosis. Treatment for tuberculosis was initiated after consult with an infectious disease specialist. The other household members were also treated after work-up. At present, she is clinically and biochemically euthyroid on levothyroxine and has completed her treatment. This case highlights that subacute thyroiditis can be a presentation of multiple etiologies and rarely of malignancy. A comprehensive workup should be carried out to identify the etiology to administer appropriate intervention. Presentation: Monday, July 14, 2025