MON-397 - Multifocal Papillary Thyroid Carcinoma Presenting as A Painful Isthmus Mass: A Case Highlighting Discordant Molecular and Sonographic Risk

Background: Papillary thyroid carcinoma (PTC) is typically an incidental, asymptomatic finding. New-onset anterior neck pain suggests benign etiologies such as subacute thyroiditis, and intranodular hemorrhage, but is an uncommon, potentially misleading presentation for malignancy, especially when arising from the thyroid isthmus.

Case: A 47-year-old woman presented with a 1-month history of a new anterior neck mass and episodic sharp pain radiating to the jaw. Thyroid function, ESR, and CRP were normal. Thyroglobulin was elevated at 232 ng/mL (normal range: 1.5-38.5 ng/mL). Ultrasound revealed two suspicious nodules: a 2.7 cm solid hypoechoic TI-RADS 4 isthmus nodule and a 0.8 cm solid hypoechoic TI-RADS 5 right-lobe nodule with microcalcifications and rim calcifications. Fine-needle aspiration/molecular results were discordant: Isthmus nodule was Bethesda IV/Afirma Suspicious (75% risk of malignancy); Right Lobe nodule was Bethesda III/Afirma Benign. Total thyroidectomy was performed, and pathology confirmed multifocal classic PTC (2.7 cm isthmus primary and 0.6 cm right-lobe focus) both confined to the thyroid with negative margins, and no lymphovascular or extrathyroidal invasion. Postoperative thyroglobulin was 0.2 ng/ml. The patient had transient post-operative complications (hypocalcemia and vocal cord paralysis) and remains under surveillance.

Discussion: This case highlights the importance of including malignancy in the differential diagnosis for painful thyroid masses. While pain is an uncommon presentation for PTC (~5% of cases), it is often associated with locally advanced disease or expansion near sensitive midline structures, such as the strap muscles or pretracheal fascia, a risk heightened by the isthmus location. This report documents the rare combination of symptomatic pain and discordant molecular results (Bethesda IV/Afirma Suspicious vs. Bethesda III/Afirma Benign) in two foci of the same primary cancer, emphasizing the diagnostic challenges of multifocal disease and the necessity of comprehensive risk stratification, regardless of initial symptom presentation.

Conclusion: New-onset anterior neck pain, especially associated with a suspicious isthmus mass, should not exclude PTC. Comprehensive work-up including imaging and tissue sampling remains critical to avoid delaying the diagnosis of this rare, yet important, clinical presentation.

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