ABSTRACTObjective:Intrathyroidal injection using an insulin pen filled with a mixture of lidocaine and triamcinolone acetonide is a therapy for subacute thyroiditis (SAT) reported by us previously. We aimed to evaluate the clinical efficacy of ultrasound-guided intrathyroidal injection in the treatment of SAT.Subjects and methods:A total of 93 patients with SAT completed the study. All patients were evaluated via a history and clinical examination followed by thyroid function tests and ultrasonography of the thyroid. After ultrasound-guided intrathyroidal injection, the patients were followed up with respect to the injection frequency, treatment duration, and patient satisfaction. The visual numerical rating scale was used as a pain questionnaire for a given interval.Results:Thyroid pain instantly decreased to scores below 3.0 following the first injection. Sixty-three patients (67.74%) avoided relapse of thyroid pain within 3 injections, which occurred within only 3 days after the first injection. The pain in 27 patients (29.03%) disappeared completely after 4-6 injections. Only 3 patients (3.23%) were found to need more than 6 injections, with 10 cited as the maximum number of injections, the injection took only 17 days altogether. The mean treatment cycle of the intrathyroidal injection was 3.98 days. There were no other associated complications with the novel therapy except infrequent small subcutaneous hematomas, which could be prevented with skilled practice. The average patient satisfaction score was as high as 9.0.Conclusion:Intrathyroidal injection of lidocaine and triamcinolone acetonide using an insulin pen was found to be an advantageous and satisfactory treatment for SAT.