Indium-111 pentetreotide single-photon emission tomography in patients with TSH-secreting pituitary adenomas: Correlation with the effect of a single administration of octreotide on serum TSH levels

Abstract

Few data are available on the visualization of somatostatin receptors in vivo in patients with thyrotropin (TSH)-secreting adenoma. We studied five patients with TSH-secreting adenomas using single-photon emission tomography (SPET) after administration of indium-111 pentetreotide. The intensity of 111In-pentetreotide uptake by the tumours was correlated with the degree of TSH suppression after a single administration of 100 microg octreotide s. c. Five patients (three women and two men) aged 27-46 years were investigated. Except for one patient with acromegaly, all had pure TSH-secreting tumours. One patient was previously untreated, while two had received octreotide, one antithyroid drugs, and one radioiodine. In all patients SPET demonstrated increased uptake of 111In-pentetreotide by the pituitary adenoma. The target to non-target ratio (T/nT) of 111In-pentetreotide uptake was higher than 10 in three patients. Administration of 100 microg octreotide s. c. caused a significant reduction in TSH levels from 4.8+/-1.4 mU/l to a nadir of 3.1+/-1.1 mU/l after 6 h (P<<0.001 by ANOVA). Suppression of TSH secretion ranged from 30% to 60% of the baseline value. The T/nT ratio showed a trend toward a direct relationship with the degree of TSH inhibition after acute octreotide administration (r=0.67; P=NS). Our study showed that 111In-pentetreotide scan visualized somatostatin receptors in all five of the patients with TSH-secreting pituitary adenomas, confirming the frequent presence of somatostatin receptors in these rare tumours, even though the correlation with the TSH inhibition after a single administration of octreotide did not reach significance.

Metabolic In Vivo Visualization of Pituitary Adenomas: a Systematic Review of Imaging Modalities

“…Two authors studied uptake of 111 In-pentreotide, a scintigraphic marker of somatostatin receptors. 16,17 Losa et al evaluated 5 TSH-secreting PAs and observed a corresponding decrease in 111 In-pentreotide uptake and serum TSH levels in the PAs following a dose of octreotide, though the trend was not statistically significant. Yonekura et al additionally observed that positive 123 I-epidepride uptake was an indirect marker of D2 receptors and was therefore valuable for diagnosis and treatment planning.…”

“…GH-secreting PAs cause acromegaly and are responsive to octreotide, a somatostatin analog; however, GH levels normalize in only 30–45% of patients following medical treatment. 12 Thyrotropin (TSH)-secreting adenomas account for 1% of all PAs and are often misdiagnosed as Graves’ disease; 16 as a result, tumors tend to be larger and more invasive when finally discovered, rendering surgical removal difficult. 16,32,33 Eradication of functional residual following surgery is only achieved in about 40% of TSH-secreting PAs, even after adjunctive radiotherapy.…”

Somatostatin Analogs as Radiodiagnostic Tools

“…A positive correlation between the increased 111 Inpentetreotide uptake in TSH-secreting pituitary adenomas and the inhibition of excessive TSH secretion by octreotide has also been shown [22,[33][34][35]. 111 Inpentetreotide scintigraphy was negative in patients with microprolactinomas and ACTH-secreting pituitary microadenomas [26].…”

Somatostatin receptor imaging for neuroendocrine tumors

“…Similarly, a positive correlation between the increased 111 In-pentetreotide uptake in TSH-secreting pituitary adenomas and the inhibition of excessive TSH secretion by octreotide has been shown [35,38]. 111 In-pentetreotide scintigraphy was negative in patients with microprolactinomas and ACTH-secreting pituitary microadenomas [37,39].…”