SUN-175 Repeat Unstimulated AVS with Aid of Plasma Metanephrines Identifies Unilateral Primary Aldosteronism When Initial AVS and Metomidate PET-CT Fails To

Introduction Adrenal venous sampling (AVS) is the reference test for identifying unilateral primary aldosteronism (PA). However, in patients with corticol co-secreting adrenal nodules, elevated cortisol levels may affect the interpretation of aldosterone-cortisol (AC) ratios. ACTH-stimulation may further confound results. In such patients, the use of plasma metanephrines instead of cortisol as a correcting factor may be helpful. Case Summary A 54 year old lady presented with 8 years of hypertension and hypokalaemia (nadir 2.2mmol/L) while on amlodipine 10mg and valsartan 80mg daily. PA was confirmed by a post-saline infusion aldosterone 1075pmol/L. CT identified a 2.4cm right lipid rich adrenal adenoma. Serum cortisol post 1mg overnight dexa-suppression test was unsuppressed at 63mmol/L. First AVS was done sequentially under ACTH stimulation and suggested lateralization to the right, with lateralization ratio (LR) 3.4. However, this was <4, and there were bilaterally low AC ratios compared to peripheral vein. Metomidate PET-CT scan then showed increased uptake over the nodule, but lower than the contralateral gland. In view of these findings, repeat AVS was done simultaneously without ACTH stimulation. Given the possibility of a co-secreting adenoma, plasma metanephrines were also measured. Second AVS showed right-sided lateralization (LR 11.8). Using metanephrines as a correction factor, the LR was even more elevated at 22.3, with contralateral suppression. She underwent right adrenalectomy and was cured of hypertension and hypokalaemia at 6 months post surgery. Aldosterone renin ratio has normalized: aldosterone <4ng/dL, plasma renin activity 0.6ng/ml/hr. Clinical Lessons While ACTH stimulation helps to improve success rates of cannulation by increasing cortisol gradients, most studies show that it lowers LR. Furthermore, this would be concerning in patients with cortisol co-secreting adenomas. In this case, repeat AVS without ACTH demonstrated improved lateralization to the right. The use of metanephrine as a correcting factor appears to be a better indicator of right sided disease. However, while plasma metanephrines have been shown to be useful to indicate correct catheter placement, it has not been adopted as a correction factor for dilution yet. Finally, in addition to affecting AVS results, cortisol-cosecreting tumors may also affect 11C-Metomidate PET-CT imaging. Conclusion In patients with suspected cortisol co-secreting adenomas, unstimulated AVS and use of plasma metanephrines may help to identify unilateral PA even when conventional AVS and metomidate scans fail to. Further studies on using metanephrines as a correcting factor for lateralisation would be helpful.