Indium-111-pentetreotide in Graves' disease.

Abstract

Thyroidal and orbital lymphocytic infiltration in Graves' disease, as well as identification of somatostatin receptors on lymphocytes, has provided a rationale for receptor imaging with the radiolabeled somatostatin analog pentetreotide. Recently, we demonstrated that in contrast to controls, Graves' patients showed markedly increased orbital accumulation of pentetreotide. Longitudinal and follow-up data are presented here. In 20 (16 hyperthyroid) Graves' patients with active eye disease, planar (thyroid) and SPECT (orbit) images were performed 4 and 24 hr after injection of 111In-pentetreotide (222 MBq) before and 3 mo after starting antithyroid and combined steroid and orbital radiotherapy. Thyroidal uptake decreased during methimazole treatment (4 hr postinjection, median: hyperthyroid 989 counts/pixel/MBq injected activity, euthyroid 253 counts, p = 0.001; 24 hr, 437 versus 95 counts/pixel/MBq, p = 0.005). Fourteen patients (70%) responded to steroid and radiotherapy. The pentetreotide orbit-to-brain ratio decreased markedly after completion of therapy (4 hr: 25 before versus 6.2 after therapy, p = 0.0003; 24 hr: 9.6 versus 2.7, p = 0.003). A high pretreatment ratio correlated with a response to therapy (p = 0.001: in 14 of 16 patients with a ratio > 10, 4 hr postinjection, ophthalmopathy improved; positive predictive value: 90%; median activity score before 6 versus 2 after therapy, p = 0.0001) in contrast to none of the four cases with a ratio less than 10 (score 5 versus 4, p = 0.08). Pentetreotide scans may be regarded as a semiobjective tool in the evaluation of Graves' disease, both at initial stages as well as during treatment.