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.

The findings establish that the imaging technique, which radioactively tags aldosterone-producing tissue with the marker ¹¹C-metomidate followed by PET-CT imaging, “is just as good” as adrenal vein sampling (AVS), declared Xilin Wu, MBBS, during a presentation at the annual meeting of the Endocrine Society.

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.

MATCHing imaging against AVS

To test the clinical utility of metomidate-based PET-CT directly against AVS, Dr. Wu and her associates enrolled 143 adults with confirmed PA and hypertension at two centers in London and one in Cambridge, England. The MATCH study cohort averaged 53 years of age; two-thirds were men, 58% were White, and 30% were Black. Their median blood pressure was 147/91 mm Hg, and they were maintained on a median of two antihypertensive drugs.

The researchers assessed every patient with both the imaging method and AVS, performed in random order and blindly scored. They then began each patient on a 1-month regimen with an MRA (usually spironolactone but eplerenone [Inspra] was also an option) to test the responsiveness of each patient’s hypertension to this drug class and to gauge their likely response to adrenalectomy. After the MRA test, the researchers assessed the lateralization tests and determined that 78 patients were appropriate candidates for unilateral adrenalectomy while the remaining 65 patients were not and continued on the MRA regimen. They recommended surgery if patients were clear positives by AVS, by PET-CT imaging, or both.

The study had four primary outcomes to assess the ability of the two diagnostic methods to predict the success of surgery based on four increasingly stringent postsurgical criteria calculated in hierarchical sequence: Partial or complete biochemical success, complete biochemical success, partial or complete clinical success (partial meaning any significant reduction in blood pressure), or complete clinical success (systolic pressure reduced to less than 135 mm Hg). Only one of the 78 patients treated with surgery failed to achieve at least a partial biochemical response.

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For each of the four metrics, ¹¹C-metomidate PET-CT produced point estimates of diagnostic accuracy that consistently edged out AVS. While these advantages were not large enough to meet the prespecified threshold for proving superiority, they comfortably showed the noninferiority of this imaging method compared with AVS.

For example, the PET-CT method had 43.6% accuracy for predicting a clinical cure, compared with 39.7% accuracy for AVS. For complete biochemical cure, imaging had 68.8% accuracy, compared with 62.3% for AVS, Dr. Wu reported.

Another notable finding from the study was how strongly a robust blood pressure response to spironolactone predicted the clinical outcome from surgery. Patients whose systolic blood pressure fell below 135 mm Hg on MRA treatment had a nearly 18-fold higher rate of achieving a complete clinical cure following surgery compared with patients who did not have as dramatic a blood pressure response to MRA treatment.

Woefully low rates of PA assessment

But regardless of the success that PET-CT imaging has for identifying surgical candidates, the first step is to identify patients with PA, a diagnosis that’s woefully underperformed worldwide. One example: A separate report at ENDO 2021 retrospectively reviewed nearly 12,000 patients with hypertension and an indication of PA, such as treatment-resistant hypertension or early-onset hypertension, and managed at either of two university outpatient clinics in Michigan during 2010-2019. The report documented that 3% underwent PA assessment.

Diagnosis of patients with PA “is a major problem,” noted Dr. D’Alessio. “I think of PA as an underdiagnosed and undertreated condition, with a huge impact on morbidity and mortality. Any advance in this area is likely to be useful.” But, he added, “I’m dubious whether this [new imaging approach] will increase diagnosis of PA.” What’s needed is “getting more primary care physicians to do more screening” for PA among their patients with hypertension and a suggestion of a PA cause.

“Surgical cures are glamorous, but medical management is also very effective, and we have good, inexpensive drugs to do this,” the MRAs, Dr. D’Alessio said.

The study received no commercial funding. Dr. Wu and her coauthors had no disclosures. Dr. D’Alessio has been a speaker on behalf of Novo Nordisk, a consultant to Intarcia and Lilly, and has received research funding from Lilly and Merck.

mzoler@mdedge.com

Imaging alternative to AVS could boost detection of primary aldosteronism