In vivo imaging of pituitary tumours using a radiolabelled dopamine D2 receptor radioligand.
OBJECTIVE
Knowledge of the dopamine D2 receptor status of pituitary tumours may play a predictive role in differential diagnosis and therapeutic decisions. This study was performed to evaluate the value of pituitary dopamine D2 receptor scintigraphy with (S)-2-hydroxy-3-123I-iodo-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl) methyl]benzamide (123I-IBZM) in the diagnostic evaluation of patients with pituitary tumours.


METHODS
Scintigraphy using 123I-IBZM was performed in 5 patients with PRL-secreting macroadenomas, 2 patients with PRL-secreting microadenomas, 17 patients with clinically non-functioning pituitary adenomas (NFPAs), 12 patients with GH-secreting adenomas and 1 patient with a TSH-secreting macroadenoma.


RESULTS
Single-photon emission tomography (SPECT) showed significant uptake of 123I-IBZM in the pituitary region in 3/5 macroprolactinoma patients. These results closely correlated with the response of plasma PRL levels to the dopamine D2 receptor agonist quinagolide. In two scan-positive prolactinoma patients, repeated SPECTs during therapy with quinagolide showed a reduction in the pituitary uptake of 123I-IBZM. Pituitary SPECT was negative in the 2 microprolactinoma patients, who responded to quinagolide administration. In 4/17 patients with NFPA, significant uptake of the radioligand in the pituitary region was observed. In 2/3 scan-positive NFPA patients, who were treated with quinagolide, shrinkage of the pituitary tumours was observed. Treatment with quinagolide resulted in stabilization of tumour growth in the other scan-positive patients. Four out of 17 patients with NFPA and a negative SPECT were treated with quinagolide. Tumour growth was observed in 1 patient, and tumour size did not change in the other 3 patients. The pituitary region of none of the 12 acromegaly patients showed significant uptake of 123I-IBZM. Sensitivity of the GH-secreting adenomas to quinagolide was demonstrated in 8/12 patients in vivo by an acute test, and in 6/9 of the tumours in vitro. Pituitary SPECT was negative in the patient with the TSH-secreting macroadenoma and this tumour also showed no sensitivity to quinagolide in vivo or in vitro.


CONCLUSIONS
We conclude that 123I-IBZM is a ligand for in vivo imaging of dopamine agonist- sensitive macroprolactinomas, but not for microprolactinomas or GH-secreting adenomas. The technique potentially provides a means of predicting the dopamine agonist-responses of non-functioning pituitary adenomas in vivo.
de Herder
W W
WW
Department of Internal Medicine III, University Hospital Rotterdam, The Netherlands.
Reijs
A E
AE
Kwekkeboom
D J
DJ
Hofland
L J
LJ
Nobels
F R
FR
Oei
H Y
HY
Krenning
E P
EP
Lamberts
S W
SW
D000236:Adenoma / Q000097:blood / Q000000981:diagnostic imaging / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000634:Aminoquinolines / Q000627:therapeutic use; D001549:Benzamides; D003287:Contrast Media; D018491:Dopamine Agonists / Q000627:therapeutic use; D018492:Dopamine Antagonists; D005260:Female; D013006:Growth Hormone / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D010902:Pituitary Gland / Q000000981:diagnostic imaging; D010911:Pituitary Neoplasms / Q000097:blood / Q000000981:diagnostic imaging* / Q000188:drug therapy; D011388:Prolactin / Q000097:blood; D015175:Prolactinoma / Q000097:blood / Q000000981:diagnostic imaging* / Q000188:drug therapy; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2 / Q000032:analysis*; D013972:Thyrotropin / Q000378:metabolism; D015899:Tomography, Emission-Computed, Single-Photon
D000634:Aminoquinolines; D001549:Benzamides; D003287:Contrast Media; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2; C046650:quinagolide; C055743:3-iodo-2-hydroxy-6-methoxy-N-((1-ethyl-2-pyrrolidinyl)methyl)benzamide; D011388:Prolactin; D013972:Thyrotropin; D013006:Growth Hormone