Indium-111-pentetreotide scintigraphy in Graves' ophthalmopathy

The radiolabeled somatostatin analog 111In-pentetreotide can sensitively demonstrate somatostatin receptor-positive localizations in diseases where activated lymphocytes play a role. Lymphocyte infiltration of retrobulbar tissue in Graves' ophthalmopathy is the rationale of receptor imaging with radionuclide-coupled 111In-pentetreotide.

Forty patients with Graves' ophthalmopathy, 5 patients with orbital myositis and 10 control subjects were included in this prospective study. Indium-111-pentetreotide (110 MBq) was intravenously injected and SPECT images were obtained at 4 and 24 hr after injection. The scans were analyzed by a region of interest technique. An uptake ratio between the orbits and the brain was determined.

Compared to controls (4-hr 111In-pentetreotide uptake: median 6.0 counts/voxel/MBq, orbit-to-brain ratio 5.6), ophthalmopathy patients showed two- to threefold increased uptake (15.8 counts/voxel/MBq versus controls p = 0.0032; ratio 12.6 versus controls p = 0.003). When considering patients with active disease only, even higher uptake was registered (16.8 counts/voxel/MBq versus controls p = 0.0048, ratio 15.6 versus controls p = 0.0006). Untreated patients showed markedly higher uptake (23 counts/voxel/MBq) compared to patients under steroid therapy (12.6, p = 0.001). In myositis, high uptake (20 counts/voxel/MBq) was also registered.

In contrast to controls, ophthalmopathy patients showed markedly increased orbital accumulation of labeled 111In-pentetreotide. This sensitive nuclear medicine technique could possibly select those patients who might benefit from treatment with immunosuppressive agents and/or octreotide.