Thyroid Tuberculosis Causing Fever of Unknown Origin in a Patient With Multinodular Goiter

Introduction: Tuberculosis (TB) involving the thyroid gland is rare and typically results in hypothyroidism. Here we report a case of thyroid TB that presented with hyperthyroidism. Clinical Case: A 54-year-old woman with a history of hyperthyroidism due to toxic multinodular goiter presented to the emergency department with fever of unknown origin associated with sore throat, non-productive cough, night sweats, diarrhea, and right anterior neck pain that worsened with coughing. Her fevers were intermittent, ranging from 38 to 39 degrees Celsius, and would subside with acetaminophen. She reported that her symptoms had started after getting a thyroid [Tc-99m] pertechnetate scan and 24 hour [I-131] sodium iodide uptake study a month prior. The scan at the time revealed hyperfunctioning thyroid nodules in the lower lobes bilaterally. The 24-hour uptake was 20.2% which is within the normal range of 7 to 30%. TSH on presentation was 0.01 mIU/L (Normal range 0.3-5.50 mIU/L), free T4 was 2.05 ng/dL (Normal range 0.76 -1.7 ng/dL), and free T3 was 5 pg/mL (Normal range 1.9-3.9 pg/mL). Exam revealed a multinodular goiter, which was firm with mild tenderness, and no cervical lymphadenopathy. Infectious workup was unremarkable other than a positive interferon-gamma release assay. As for TB risk factors, the patient immigrated to the United States from Albania about 13 years prior. The patient denied any known TB exposure, neither had she been treated for TB. Radiograph and computed tomography (CT) of the thorax were unremarkable other than re-demonstration of the multinodular goiter. Fluorodeoxyglucose-18 positron emission tomography (FDG-PET), which was performed to identify any focus of active TB, had revealed intense, infiltrative, heterogeneous FDG uptake of the nodular thyroid gland with reactive level 3 and 4 cervical lymph nodes. Also, the scan revealed hyper-metabolic hilar, pre-tracheal, and sub-carinal lymph nodes which could represent latent TB. Further workup for any other foci of active TB including broncho-alveolar lavage, sputum cultures, lumbar puncture, and bone marrow biopsy were unremarkable. Thyroid ultrasound revealed 2 right sided and 3 left sided thyroid nodules, mostly solid and hypoechoic. Fine needle aspiration of nodules revealed benign follicular nodules bilaterally, however the left aspirate contained loose aggregates of histiocytes consistent with non-necrotizing granulomas. Acid-fast bacilli stain of the aspirate was negative. The patient was started on therapy for active TB with isoniazid, rifampin, pyrazinamide, and ethambutol. Six weeks after treatment her fevers had resolved. Conclusion: Thyroid TB should be considered when the severity of symptoms cannot be explained by the degree of hyperthyroidism alone in patients with increased risk of TB. Additionally, TB in the thyroid can be challenging to identify in a patient with known underlying thyroid disease.