Grey scale thyroid ultrasonography in the evaluation of patients with Graves' disease.

Abstract

Graves’ disease is a genetically induced autoimmune disorder characterized by hyperthyroidism due to circulating thyroid stimulating hormone (TSH) receptor autoantibodies (TRAb) with thyroid stimulating activity (1). Graves’ disease is the most common cause of hyperthyroidism, which has an estimated prevalence in iodine sufficient areas of 20/1000 females and 2.3/ 1000 males (2). It is most common in females between the ages of 20 and 50 years, but it may occur at any age. The laboratory diagnosis of Graves’ disease is based on the finding of high serum thyroid hormone and undetectable serum TSH concentrations associated with circulating thyroglobulin and thyroperoxidase antibodies. TRAb is detectable in almost 90% of patients, but usually it is not needed for the diagnosis. Radioisotope scan of the thyroid shows a diffuse and homogeneous radionuclide uptake. Treatment strategies for Graves’ hyperthyroidism include medical therapy with antithyroid drugs (ATD) or thyroid ablation with 131 I or surgery. ATD, mainly thionamides, inhibit thyroid hormone synthesis by blocking iodine organification catalysed by thyroid peroxidase. Treatment of Graves’ disease with thionamides is mainly performed in Europe and in Japan, while in the USA and Canada radioiodine is commonly preferred as the first choice treatment (3). Many studies have been undertaken to find parameters which help predict the clinical outcome of Graves’ hyperthyroidism after ATD withdrawal. Among them, TRAb measurement at the end of an ATD course was found to be the most predictive (4, 5). After its introduction into clinical practice in the late sixties, thyroid ultrasonography (US) proved to be very effective in the diagnostic approach to thyroid diseases, the anatomical location of the gland being advantageous for this technique. The most widely used application of thyroid US is identification and characterization of thyroid nodules (6). Rapid improvements in the development of US equipment have made available real-time high frequency transducers (7.5‐ 10 MHz) with high resolution, which allow a more precise definition of the echostructure of the thyroid tissue. In addition, recently developed color Doppler technology allows determination of the blood flow through the gland, offering the possibility of recording objective measurements, such as the peak systolic velocity of the blood flow at the level of thyroid arterial vessels (i.e. inferior thyroid artery). Using these techniques, thyroid blood flow has been shown to be correlated with the thyroid status in patients with Graves’ disease, being markedly increased in 17/18 patients with untreated active hyperthyroidism and less clearly increased in treated patients. In patients with Hashimoto’s thyroiditis, the thyroid blood flow was not correlated to thyroid status or treatment and was never markedly increased (7). Color Doppler sonography was also shown to be useful in distinguishing cases of destructive thyrotoxicosis by amiodarone (i.e. amiodarone thyrotoxicosis type 2), characterized by a low thyroid blood flow, from cases in which thyroid hyperfunction also occurs (i.e. amiodarone thyrotoxicosis type 1), characterized by an increased thyroid