Imaging alternative to AVS could boost detection of primary aldosteronism

A noninvasive imaging method for identifying whether the source of a patient’s primary aldosteronism is from unilateral or bilateral adrenal adenomas worked as well as the standard method, invasive adrenal vein sampling, in a head-to-head comparison with 143 patients.

This noninvasive alternative, which also does not require the substantial technical expertise that AVS demands, should make assessment of adenoma laterality in patients with primary aldosteronism (PA) much more widely available and accessible, predicted Dr. Wu, a researcher at Queen Mary University of London.

“It will allow more places to do this, and I think it will definitely allow more patients to be diagnosed” with PA from a unilateral source. AVS “is a real bottleneck,” she said. “We hope metomidate, or molecular imaging using other selective radiotracers, will enable many more patients to be diagnosed and appropriately managed.” Creating new diagnostic options for patients with PA and potentially increasing the number of these patients who are surgical candidates “is the aim of this study.”

Patients with PA develop a curable form of hypertension if their excess aldosterone can be neutralized with a mineralocorticoid receptor antagonist (MRA), or even more definitively by surgical removal of the adrenal aldosteronoma generating the hormonal excess as long as the adenoma is unilateral. Conventional imaging of the adrenals with CT or MRI has proven unreliable for identifying adrenal nodules noninvasively, which has made the invasive and technically challenging standard option of AVS the only game in town.

But some endocrinologists caution that the results from this one study do not suffice to make ¹¹C-metomidate-based PET-CT imaging a widely used alternative.
 

‘This is a first step.’

“This study is a first step. It will take lots more data for endocrinologists to buy into a scan over AVS,” commented David A. D’Alessio, MD, professor and chief of the division of endocrinology and metabolism at Duke University in Durham, N.C.

But Dr. D’Alessio also acknowledged the clear benefits from a safe and effective alternative to AVS.

“A reliable, less invasive, and less technical means of lateralizing excess aldosterone production would increase the number of people [with a unilateral PA source] going to surgery. The reality is that, if you are not a patient at the Mayo Clinic . . .or the National Institutes of Health, then AVS is a bit of crap shoot” that is very operator and institution dependent for its accuracy, Dr. D’Alessio said in an interview.

Metomidate specifically binds to key enzymes of the adrenal corticosteroid biosynthetic pathway, making it a precise targeting agent for a radioactive tag as documented almost a decade ago. One limitation is that this radiotracer labeling of metomidate has a 20-minute half life, which means it must be produced on site, thereby making the technology out of reach for locations that can’t set up this capability.