Adrenal imaging with iodomethyl-norcholesterol (I-131) in primary aldosteronism

Twenty consecutive patients with primary aldosteronism (PAl) underwent dexamethasone suppression (DS) imaging with 6beta-[131I]-iodomethyl-19-norcholesterol (NP-59): A) to establish the value of the adrenal scan in distinguishing aldosteronomas from bilateral hyperplasia; b) to determine its ability to locate aldosteronomas when present; and c) to compare the efficacy of NP-59 in this current series against that reported previously with NM-145 in PAl. Ten of twenty patients had an aldosteronoma, five had histologically confirmed hyperplasia, and five had presumed hyperplasia. With NP-59, nine of ten tumors were correctly located (90%) , correct distinction between tumor and hyperplasia was possible in 90%, and a locating DS scan was specific for tumor in 90%. In a combined series of different patients with PAl imaged with NM-125, 21 of 25 tumors were correctly located (84%), tumor was distinguished from hyperplasia in 86%, and the specificity of the localizing scan was 92%. The imaging delay required from tracer injection to attainment of an interpretable scan averaged 2.7 days with NP-59 and 4.8 days with NM-145. In summary, no significant differences were noted in the clinical results achieved with these two agents. The preferred agent is NP-59, since the study can be completed with less average time delay than is possible with NM-145.