Follicular Thyroid Cancer with Pulmonary Metastasis Presenting as Toxic Autonomously Functioning Thyroid Nodule

Objective: We report the case of a patient in whom a toxic autonomously functioning thyroid nodule (AFTN) turned out to be an aggressive follicular carcinoma with pulmonary metastases and subclinical hyperthyroidism. Methods: In this case study, we review the presentation, evaluation, diagnosis, and management of an aggressive follicular carcinoma presenting as an AFTN with hyperthyroidism. We also reviewed potential pitfalls in the diagnosis of this rare presentation of thyroid cancer when following the current standards of care in managing thyroid nodules. Results: An 85-year-old female with atrial fibrillation was seen for an enlarging right thyroid nodule. Biochemical testing revealed subclinical hyperthyroidism. An enlarged, 4.2 × 3.4 × 4.1-cm right thyroid lobe nodule was noted on ultrasound and confirmed to be an AFTN by thyroid scintigraphy. Incidental pulmonary nodules were noted on computed tomography (CT) and found to be fluorodeoxyglucose (FDG)-avid on positron emission tomography (PET). She was treated with total thyroidectomy, and pathologic analysis confirmed the presence of a unifocal follicular thyroid carcinoma (FTC) with lymphovascular invasion. Postoperatively, she was also treated with radioactive iodine and levothyroxine suppressive therapy. Subsequent progression of metastasis ensued, and she died approximately 4 years after diagnosis. Conclusion: Hyperthyroidism resulting from a functioning thyroid tumor is exceedingly rare. Flexibility in the approach to functioning thyroid nodules is essential. Our case demonstrates that thyroid malignancy in an AFTN should be suspected in elderly patients with rapidly growing nodules. Abbreviations: AFTN autonomously functioning thyroid nodule CT computed tomography FDG fluorodeoxyglucose FNA fine needle aspiration FTC follicular thyroid carcinoma 131-I radioactive iodine PET positron emission tomography Tg thyroglobulin TSH thyroid-stimulating hormone