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The Quarterly Journal of Nuclear Medicine 1999 September;43(3):179-87


language: English

Scintigraphy with 99mTc-pertechnetate in the evaluation of functional thyroidal autonomy

Meller J., Becker W.

From the Department of Nuclear Medicine Georg August University, Göttingen, Germany


Iodine defi­cien­cy and ­iodine defi­cien­cy dis­or­ders are ­still ­present in sev­er­al ­parts of Europe. Sonography is nei­ther spe­cif­ic in the diag­no­sis nor sen­si­tive in the eval­u­a­tion of the ­amount of auton­o­mous thy­roid tis­sue. Thyroidal auton­o­my is ­defined as a func­tion­al ­state of the thy­roid and there­fore ­only func­tion­al scin­ti­graph­ic imag­ing, pref­er­ably per­formed ­with 99mTc-per­tech­ne­tate (99mTcO4-), ­will ­offer ­both ­high sen­si­tiv­ity and spec­i­fic­ity in its diag­no­sis. Recently the clon­ing and char­ac­ter­isa­tion of the Na+/I- sym­port­er (NIS) ­offered a deep­er under­stand­ing of ­iodine and per­tech­ne­tate ­uptake in the thy­roid ­gland. Overexpression of the Na+/I- sym­port­er fol­low­ing acti­va­tion of the aden­y­late-­cyclase-cAMP-cas­cade has ­been dem­on­strat­ed in hot nod­ules, ­which ­gives for the ­first ­time an expla­na­tion for the ­enhanced ­iodine clear­ance of auton­o­mous thy­roid­al tis­sue on a molec­u­lar lev­el. The scin­ti­graph­ic eval­u­a­tion of thy­roid­al auton­o­my is per­formed ­both as a quan­ti­ta­tive and qual­ita­tive thy­roid scin­tig­ra­phy, ­using a gam­ma cam­e­ra fit­ted ­with an on-­line com­put­er ­system. A ­strong and lin­e­ar cor­re­la­tion ­between the glo­bal 99mTc-per­tech­ne­tate thy­roid ­uptake (­TCTU) and 123I clear­ance has ­been rec­og­nised. Therefore ­TCTU-val­ues can be ­used as a reli­able equiv­a­lent of the ­iodine clear­ance in the eval­u­a­tion of actu­al thy­roid func­tion. The clin­i­cal val­ue of the ­TCTU in the diag­no­sis of thy­roid­al auton­o­my is lim­it­ed ­because it rep­re­sents ­iodine clear­ance of ­both nor­mal and auton­o­mous tis­sue. As a con­se­quence scin­ti­graph­ic diag­no­sis and quan­tifi­ca­tion of auton­o­my can ­only be estab­lished if the glo­bal 99mTc-per­tech­ne­tate thy­roid ­uptake ­under sup­pres­sion (TCTUs) is deter­mined. This meth­od is sen­si­tive in ­risk strat­ifi­ca­tion of spon­ta­ne­ous or ­iodine ­induced hyper­thyr­oi­dism, in the esti­ma­tion of the tar­get vol­ume ­prior to radio­io­dine ther­a­py inde­pen­dent­ly of its dis­tri­bu­tion and in the eval­u­a­tion of ther­a­peu­tic suc­cess ­after defin­i­tive ther­a­py.

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