Papillary Thyroid Carcinoma Revealed by a Toxic Nodule: A Case Report and Literature Review

Abstract Hyperfunctioning thyroid nodules are classically considered benign, leading to a generally reassuring diagnostic approach. However, recent studies suggest that the risk of malignancy, although low, is not negligible. We report a rare case of papillary thyroid carcinoma revealed within a toxic thyroid nodule and review the relevant literature to highlight diagnostic and therapeutic implications. A 38-year-old woman presented with an anterior cervical swelling and respiratory discomfort. Biological assessment showed subclinical hyperthyroidism. Cervical ultrasound revealed a left lobar solid–cystic nodule classified EU-TIRADS 3, and 99mTc Pertechnetate Thyroid scintigraphy demonstrated a nearly total autonomous hyperfunctioning left-lobe nodule. Owing to compressive symptoms from a plunging goiter, total thyroidectomy was performed. Histopathological examination unexpectedly revealed a classic papillary thyroid carcinoma confined to the thyroid (pT2NxMx) with vascular emboli. The patient subsequently underwent radioactive iodine ablation with 3.7 GBq of I-131, followed by suppressive L-thyroxine therapy. Post-therapy whole-body scintigraphy showed only residual thyroid bed uptake, and follow-up demonstrated undetectable thyroglobulin levels with no evidence of recurrence. This case illustrates that malignancy can occur in autonomously functioning thyroid nodules, even when ultrasound features suggest low to intermediate risk. It underscores the limitations of relying solely on hyperfunctionality or TIRADS classification to exclude cancer. An integrated approach combining clinical context, ultrasound, scintigraphy, and, when indicated, cytology is essential. Early recognition and appropriate management allow outcomes comparable to those of differentiated thyroid carcinoma diagnosed in euthyroid settings. Keys words: Papillary thyroid carcinoma; Toxic thyroid nodule, Radioactive iodine therapy.