Rapidly progressive Riedel's thyroiditis presenting with recurrent laryngeal nerve palsy mimicking thyroid malignancy

Riedel's thyroiditis is an extremely rare fibrosing inflammatory disorder that extends beyond the thyroid capsule into surrounding structures. The disease usually progresses slowly; however, we report an unusual case with rapid progression that closely mimicked malignancy.An Asian woman in her 50s developed throat discomfort, hoarseness and a neck mass within 1 month. Laryngoscopy revealed left vocal cord paresis. Ultrasonography demonstrated a rapidly enlarging hypoechoic mass and fine-needle aspiration cytology suggested possible malignancy. Total thyroidectomy with lymph node dissection was, therefore, performed. Histopathological examination revealed dense fibrosis and obliterative phlebitis, consistent with Riedel's thyroiditis. The patient's hoarseness improved postoperatively, and she remains well 2.5 years later on levothyroxine monotherapy.This case illustrates that Riedel's thyroiditis can rarely present with acute progression and recurrent laryngeal nerve palsy, closely mimicking thyroid cancer. Early surgical intervention provided both a definitive diagnosis and effective treatment.