Octreoscan in Thyroid-Associated Ophthalmopathy

Abstract

Until recently, there was no imaging technique available that could be considered as a reliable measure of inflammation in thyroid-associated opthalmopathy (TAO). Pentetreotide (a synthetic derivative of somatostatin) labeled with ¹¹¹In has been used to visualize somatostatin receptors in endocrine-related tumours in vivo. It has also been used to measure the orbital uptake in patients with TAO. An increased uptake in the orbit was found in patients with active disease. It was suggested that it is caused by the expression of somatostatin receptors on activated T-lymphocytes. Thus, a positive orbital octreoscan indicates clinically active eye disease in which immunosuppressive treatment might be of therapeutic benefit, in contrast to the fibrotic end stage. Indeed, successful immunosuppression with prednisone, orbital irradiation, or very recently with somatostatin analogues, has been demonstrated in patients with TAO and positive octreoscan. It is inferred that an orbital octreoscan is mainly indicated to select patients with TAO who will benefit from immunosuppression. However, limitations such as cost, nonnegligible radiation burden, nonspecific examination for TAO, and finally, lack of evaluation of eye muscle swelling restrict the widespread use of this technique. It remains to be seen if orbital octreoscan will become a widely available tool in the management of patients with TAO.