The Value of Ultrasonography in the Diagnosis and Follow-up of Subacute Thyroiditis

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Abstract
Twenty-three consecutive patients with clinical and biochemical suspicion of subacute thyroiditis (SAT) were evaluated by ultrasonic scanning of the thyroid. Ultrasonic findings supported the diagnosis in all cases. In the 16 patients in whom thyroid scintigraphy was performed this was compatible with SAT. Initially, median thyroid volume was 40 mL (range 20-289) and a very low echogenicity was demonstrated in all patients. The extension of hypoechogenicity exceeded 75% in the majority of patients. Thyroid volume was significantly reduced to a median of 13 mL (range 9-40) (68% reduction, p < 0.00001) at a median follow-up period of 18 months (range 6-33) and a majority of the patients (60%) had persistent morphological abnormalities. No correlation between thyroid function and the extension of hypoechogenicity initially or at end of follow-up could be demonstrated. Recurrence was noted in 8 patients (35%), two of whom were positive for anti-TPO antibodies, but the risk of recurrence could not be correlated to the extension of hypoechogenicity or initial thyroid function. Recurrence was related to the further extention of hypoechoic areas and increase in thyroid volume, as evidenced by ultrasonography in our series. None developed thyroid antibodies, and all were euthyroid at the end of the observation period. We believe that high resolution ultrasonography has a useful supporting role in the diagnosis of subacute thyroiditis. In case of doubt and differential diagnostic considerations, it facilitates guided biopsies. Additionally, it allows determination of disease activity and thyroid size.