Imaging of dopamine D2 and somatostatin receptors in vivo using single-photon emission tomography in a patient with a TSH/PRL-producing pituitary macroadenoma

Abstract

A 28-year-old man with a thyroid stimulating hormone/prolactin (TSH/PRL)-secreting pituitary macroadenoma is discussed in relation to dopamine D2 and somatostatin receptor single-photon emission tomography (SPET). The patient presented with decreased vision in the left eye as a result of a temporal visual field defect and with mild hyperthyroidism. Medical therapy was tried. A test dose of both octreotide and bromocriptine resulted in an acute reduction in serum levels of TSH, alpha-subunits and PRL, whereas there was no response to TRIAC. Somatostatin and dopamine D2 receptors were present on the tumour as visualised by SPET with the ligands indium-111 diethylene triamine penta-acetic acid (DTPA)-octreotide (111In-SMS) and iodine-123 iodobenzamide (123I-IBZM), respectively. Therefore, treatment with octreotide 150 micrograms t.i.d. subcutaneously and bromocriptine 10 mg b.i.d. orally was given for > 12 and > 6 weeks, respectively. Following this treatment the visual defects disappeared, although tumour size, as measured by CT scanning, and serum TSH levels did not decrease. SPET with 111In-SMS and 123I-IBZM after therapy revealed no change or a possible increase in somatostatin receptor binding potential and a possible decrease in dopamine D2 receptor binding potential. The lack of long-term effects of the medical treatment is discussed. It is concluded that a high somatostatin and dopamine D2 receptor binding potential in vivo in a TSH/PRL-producing adenoma does not necessarily predict a successful outcome of medical treatment.

Thyrotropin-Secreting Pituitary Tumors*

“…Moreover, in vivo evidence for both SRIH and dopamine D2 receptors was obtained by Verhoeff et al (175) by using single photon emission tomography with in In-octreotide and [ I]iodobenzamide. The absence of clear correlation with the tumor size reduction on octreotide and bromocriptine treatment suggests that this technique may not predict the successful outcome of medical treatment.…”

Hormone levels and tumour size response to quinagolide and cabergoline in patients with prolactin‐secreting and clinically non‐functioning pituitary adenomas: predictive value of pituitary scintigraphy with 123I‐methoxybenzamide

“…Recently, the presence of Dz receptors on pituitary tumours was demonstrated in vivo by means of single-photon emission computed tomography (SPET) using 'zI-methoxybenzamide ('%BZM) and '231-epidepride (de Herder et al, 1996;Pirker et al, 1996;Ferone et al, 1998;de Herder et al, 1999). A significant correlation between tracer uptake in the pituitary adenoma and clinical response to quinagolide or bromocriptine treatment was observed in a few selected patients with PRL-, GH-or a-subunit secreting adenomas (Verhoeff et al, 1993;Scillitani et al, 1995;de Herder et al, 1996;Pirker et al, 1996;Ferone et al, 1998;de Herder et al, 1999). This approach might be of great clinical relevance in patients with NFA, in whom the lack of biochemical markers makes the monitoring of the efficacy of pharmacotherapy very difficult.…”

In vivo imaging of pituitary tumours using a radiolabelled dopamine D2 receptor radioligand

“…Variable effects of dopamine agonists in TSH-secreting tumours have been reported, and suppression of the inappropriate TSH secretion by these agents has been demonstrated in a few cases (Karlsson et al, 1993;Verhoeff et al, 1993).…”