Predicting Treatment Response in Primary Aldosteronism Using 11C-Metomidate Positron Emission Tomography

Background Appropriate treatment of primary aldosteronism (PA) depends on accurate lateralization. 11C-metomidate (MTO) is a tracer used in PET that provides functional information about the adrenal cortex. We aimed to perform MTO PET for patients with PA who are managed according to the guideline and to verify its correlation with other lateralization modalities and usefulness in outcome prediction. Methods Seventeen patients with PA who underwent MTO PET and had ≥1 lateralization modality (adrenal venous sampling and/or NP-59 adrenal scintigraphy) were included. SUVmax of each adrenal gland (higher uptake side, HSUVmax; lower uptake side, LSUVmax) and the ratio of HSUVmax to LSUVmax (contrast) were compared with lateralization modalities, postsurgical outcomes, and medical treatment outcomes. Cutoff values were used as outcome predictors. Results HSUVmax and LSUVmax increased in the order of bilateral, unilateral, and negative findings of CT, with opposite order of contrast. High discordant rate between MTO PET and other lateralization modalities was noted. Biochemical responders (n = 8) had significantly lower HSUVmax and LSUVmax than nonresponders, and clinical responders (n = 6) had borderline lower HSUVmax than nonresponders. By optimal cutoff values of HSUVmax and LSUVmax, MTO PET was able to predict biochemical and clinical outcomes in patients with medical treatment. Conclusion According to adrenal CT findings, MTO PET presented different uptake patterns. Patients with PA under medical treatment showed significantly lower tracer uptake in responders. Thus, MTO PET may be a useful imaging biomarker to predict medical treatment outcome. Multicenter prospective study with a larger number of patients is needed for further validation.