IMAGING OF DOPAMINE D2 AND SOMATOSTATIN RECEPTORS INVIVO USING SINGLE-PHOTON EMISSION TOMOGRAPHY IN A PATIENT WITH A TSH PRL-PRODUCING PITUITARY MACROADENOMA

A 28-year-old man with a thyroid stimulating hormone/prolactin (TSH/PR L)-secreting pituitary macroadenoma is discussed in relation to dopami ne D2 and somatostatin receptor single-photon emission tomography (SPE T). The patient presented with decreased vision in the left eye as a r esult of a temporal visual field defect and with mild hyperthyroidism. Medical therapy was tried. A test dose of both octreotide and bromocr iptine resulted in an acute reduction in serum levels of TSH, alpha-su bunits and PRL, whereas there was no response to TRIAC. Somatostatin a nd dopamine D2 receptors were present on the tumour as visualised by S PET with the ligands indium-111 diethylene triamine penta-acetic acid (DTPA)-octreotide (In-111-SMS) and iodine-123 iodobenzamide (I-123-IBZ M), respectively. Therefore, treatment with octreotide 150 mug t.i.d. subcutaneously and bromocriptine 10 mg b.i.d. orally was given for > 1 2 and > 6 weeks, respectively. Following this treatment the visual def ects disappeared, although tumour size, as measured by CT scanning, an d serum TSH levels did not decrease. SPET with In-111-SMS and I-123-IB ZM after therapy revealed no change or a possible increase in somatost atin receptor binding potential and a possible decrease in dopamine D2 receptor binding potential. The lack of long-term effects of the medi cal treatment is discussed. It is concluded that a high somatostatin a nd dopamine D2 receptor binding potential in vivo in a TSH/PRL-produci ng adenoma does not necessarily predict a successful outcome of medica l treatment.