Imaging of dopamine D2 and somatostatin receptors in vivo 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/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.
Verhoeff
N P
NP
Department of Nuclear Medicine, Academic Medical Centre, Amsterdam Zuidoost, The Netherlands.
Bemelman
F J
FJ
Wiersinga
W M
WM
van Royen
E A
EA
D000284:Administration, Oral; D001971:Bromocriptine / Q000008:administration & dosage*; D006801:Humans; D007279:Injections, Subcutaneous; D008297:Male; D008875:Middle Aged; D015282:Octreotide / Q000008:administration & dosage*; D010911:Pituitary Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy; D015175:Prolactinoma / Q000000981:diagnostic imaging* / Q000188:drug therapy; D017448:Receptors, Dopamine D2; D017481:Receptors, Somatostatin; D013972:Thyrotropin / Q000378:metabolism*; D015899:Tomography, Emission-Computed, Single-Photon
D017448:Receptors, Dopamine D2; D017481:Receptors, Somatostatin; D001971:Bromocriptine; D013972:Thyrotropin; D015282:Octreotide