The role of octreoscan in thyroid eye disease

Until recently there was no imaging technique available which could demonst rate pathological changes in orbital tissues and could be regarded as a rel iable measure of inflammation in thyroid eye disease (TED). Pentetreotide ( a synthetic derivative of somatostatin) labelled with In-111 has been used to localize tumours which possess surface or membrane receptors for somatos tatin in vivo using a gamma camera (1). This technique visualizes somatosta tin receptors in endocrine-related tumours in vivo and predicts the inhibit ory effect of the somatostatin analogue octreotide on hormone secretion by the tumours (1), By applying In-111-DTPA-D-Phe octreotide scintigraphy (oct reoscan), accumulation of the radionuclide was also detected in both the th yroid and orbit of patients with Graves' disease (2 - 4). If peak activity in the orbit 5 h after injection of radiolabelled octreotide is set at 100% , a decrease to 40+/-4% is found at 24 h, significantly different from the decrease in blood pool radioactivity: which is 15+/-4% at 24 h. Accumulatio n of the radionuclide is most probably due to the presence in the orbital t issue of activated lymphocytes bearing somatostatin receptors (5). Alternat ive explanations are binding to receptors on other cell types (e.g. myoblas ts, fibroblasts or endothelial cells) or local blood pooling due to venous stasis by the autoimmune orbital inflammation.