Diagnostic value of adrenal iodine-131 6-beta-iodomethyl-19-norcholesterol scintigraphy for primary aldosteronism: a retrospective study at a medical center in North Taiwan

[131I]6ß-Iodomethyl-19-norcholesterol SPECT/CT for the Lateralization of Mineralocorticoid Overproduction in Primary Aldosteronism

Primary: aldosteronism is a frequent cause of secondary hypertension. With access to specialized care, an increasing number of patients with aldosteronism are being identified. Primary aldosteronism is treatable by adrenal surgery if aldosterone excess originates from one of the two, and not from both, adrenals. Bilateral hyperplasia requires lifelong mineralocorticoid receptor antagonist treatment. Up till now, adrenal venous sampling (AVS) has been widely used to distinguish between one-sided and two-sided aldosterone overproduction and patient selection for surgery. AVS is an invasive technique, and the unsuccessful sampling of the right adrenal vein during AVS often prevents side comparison, making the AVS procedure useless. Molecular imaging using [131I]6ß-iodomethyl-19-norcholesterol with SPECT CT imaging (SPECT/CT) may be a potential alternative.

METHODS

In 42 consecutive patients with confirmed primary aldosteronism, molecular imaging has been performed. After dexamethasone suppression of the non-affected adrenal tissue, 37 MBq [131I]6ß-iodomethyl-19-norcholesterol was injected i.v., and SPECT/CT images were taken 7 days later. Based on the visual evaluation of the images by two nuclear medicine specialists, patients with one-sided tracer accumulation underwent adrenalectomy. To identify a SPECT/CT parameter that best characterizes the side difference, the maximum counts and the mean counts of spherical VOIs were analyzed.

RESULTS

Of the 42 patients, 24 had one-sided aldosterone overproduction by SPECT/CT. After surgical removal of the involved adrenal, all 24 patients with SPECT/CT-identified unilateral aldosteronism achieved biochemical cure, defined as a normalized potassium level combined with an aldosterone-to-renin ratio ≤ 30. To identify the best measurable parameter of SPECT/CT side difference, the mean counts and maximum counts of a series of spherical VOIs of different diameters were analyzed. The ratio of the mean counts of 3 cm spherical VOIs of the right and left adrenal regions (lateralization index) was the best discriminator; a ratio of ≥1.29 was characteristic of one-sided disease, without overlap between the one-sided and two-sided patient groups.

CONCLUSIONS

[131I]6ß-iodomethyl-19-norcholesterol SPECT/CT with a count-based image interpretation and side-ratio calculation may be an equipollent non-invasive substitute for adrenal venous sampling in the lateralization of mineralocorticoid overproduction. It reliably identifies unilateral disease and facilitates patients' selection for surgical intervention. If confirmed by others, this functional imaging may replace AVS when lateralization is required for management decisions in primary aldosteronism.

Strategies for subtyping primary aldosteronism

Adrenal venous sampling (AVS) is a crucial method for the lateralization of primary aldosteronism (PA). It is advised to halt the use of the patient's antihypertensive medications and correct hypokalemia prior to undergoing AVS. Hospitals equipped to conduct AVS should establish their own diagnostic criteria based on current guidelines. If the patient's antihypertensive medications cannot be discontinued, AVS can be performed as long as the serum renin level is suppressed. The Task Force of Taiwan PA recommends using a combination of adrenocorticotropic hormone stimulation, quick cortisol assay, and C-arm cone-beam computed tomography to maximize the success of AVS and minimize errors by using the simultaneous sampling technique. If AVS is not successful, an NP-59 (131 I-6-β-iodomethyl-19-norcholesterol) scan can be used as an alternative method to lateralize PA. We depicted the details of the lateralization procedures (mainly AVS, and alternatively NP-59) and their tips and tricks for confirmed PA patients who would consider to undergo surgical treatment (unilateral adrenalectomy) if the subtyping shows unilateral disease.

Diagnostic Accuracy of Adrenal Iodine-131 6-Beta-Iodomethyl-19-Norcholesterol Scintigraphy for the Subtyping of Primary Aldosteronism

PURPOSE

To evaluate the diagnostic accuracy of the 131I-6β-iodomethyl-19-norcholesterol (NP-59) adrenal scintigraphy for the subtyping diagnosis of primary aldosteronism (PA), considering as gold standard for the diagnosis of unilateral PA (UPA), either the results of the adrenal venous sampling (AVS) or the outcome after adrenalectomy.

METHODS

A retrospective multicenter study was performed on PA patients from 14 Spanish tertiary hospitals who underwent NP-59 scintigraphy with an available subtyping diagnosis. Patients were classified as UPA if biochemical cure was achieved after adrenalectomy or/and if an AVS lateralization index > 4 with ACTH stimulation or >2 without ACTH stimulation was observed. Patients were classified as having bilateral PA (BPA) if the AVS lateralization index was ≤4 with ACTH or ≤2 without ACTH stimulation or if there was evidence of bilateral adrenal nodules >1 cm in each adrenal gland detected by CT/MRI.

RESULTS

A total of 86 patients with PA were included (70.9% (n = 61) with UPA and 29.1% (n = 25) with BPA). Based on the NP-59 scintigraphy results, 16 patients showed normal suppressed adrenal gland uptake, and in the other 70 cases, PA was considered unilateral in 49 patients (70%) and bilateral in 21 (30%). Based on 59-scintigraphy results, 10.4% of the patients with unilateral uptake had BPA, and 27.3% of the cases with bilateral uptake had UPA. The AUC of the ROC curve of the NP-59 scintigraphy for PA subtyping was 0.812 [0.707-0.916]. Based on the results of the CT/MRI and NP-59 scintigraphy, only 6.7% of the patients with unilateral uptake had BPA, and 24% of the cases with bilateral uptake had UPA. The AUC of the ROC curve of the model combining CT/MRI and 59-scintigraphy results for subtyping PA was 0.869 [0.782-0.957].

CONCLUSION

The results of NP-59 scintigraphy in association with the information provided by the CT/MRI may be useful for PA subtyping. However, their diagnostic accuracy is only moderate. Therefore, it should be considered a second-line diagnostic tool when AVS is not an option.

Advances in the molecular imaging of primary aldosteronism

Primary aldosteronism (PA) is the most common cause of secondary hypertension. It predisposes to adverse outcomes such as nephrotoxicity and cardiovascular damage, which are mediated by direct harm from hypertension to the target organs. Accurate subtype diagnosis and localization are crucial elements in choosing the type of treatment for PA in clinical practice since the dominant side of aldosterone secretion in PA affects subsequent treatment options. The gold standard for diagnosing PA subtypes, adrenal venous sampling (AVS), requires specialized expertise, the invasive nature of the procedure and high costs, all of which delay the effective treatment of PA. Nuclide molecular imaging is non-invasive and has wider applications in the diagnosis and treatment of PA. This review aims to provide a summary of the application of radionuclide imaging in the diagnosis, treatment management and prognostic assessment of PA.

Development of Fluorinated NP-59: A Revival of Cholesterol Use Imaging with PET

Imaging of cholesterol use is possible with the ¹³¹I scintiscanning/SPECT agent NP-59. This agent provided a noninvasive measure of adrenal function and steroid synthesis. However, iodine isotopes resulted in poor resolution, manufacturing challenges, and high radiation dosimetry to patients that have limited their use and clinical impact. A ¹⁸F analog would address these shortcomings while retaining the ability to image cholesterol use. The goal of this study was to prepare and evaluate a ¹⁸F analog of NP-59 to serve as a PET imaging agent for functional imaging of the adrenal glands based on cholesterol use. Previous attempts to prepare such an analog of NP-59 have proven elusive. Preclinical and clinical evaluation could be performed once the new fluorine analog of NP-59 production was established. Methods: The recent development of a new reagent for fluorination along with an improved route to the NP-59 precursor allowed for the preparation of a fluorine analog of NP-59, FNP-59. The radiochemistry for the ¹⁸F-radiolabeled ¹⁸F-FNP-59 is described, and rodent radiation dosimetry studies and in vivo imaging in New Zealand rabbits was performed. After in vivo toxicity studies, an investigational new drug approval was obtained, and the first-in-humans images with dosimetry using the agent were acquired. Results: In vivo toxicity studies demonstrated that FNP-59 is safe for use at the intended dose. Biodistribution studies with ¹⁸F-FNP-59 demonstrated a pharmacokinetic profile similar to that of NP-59 but with decreased radiation exposure. In vivo animal images demonstrated expected uptake in tissues that use cholesterol: gallbladder, liver, and adrenal glands. In this first-in-humans study, subjects had no adverse events and images demonstrated accumulation in target tissues (liver and adrenal glands). Manipulation of uptake was also demonstrated with patients who received cosyntropin, resulting in improved uptake. Conclusion: ¹⁸F-FNP-59 provided higher resolution images, with lower radiation dose to the subjects. It has the potential to provide a noninvasive test for patients with adrenocortical diseases.

Evolution of the cardiometabolic profile of primary hyperaldosteronism patients treated with adrenalectomy and with mineralocorticoid receptor antagonists: results from the SPAIN-ALDO Registry

OBJECTIVE

To analyze the evolution of the cardiometabolic profile of patients with primary hyperaldosteronism (PA) after the treatment with surgery and with mineralocorticoid receptor antagonists (MRA).

DESIGN

Retrospective multicentric study of patients with PA on follow-up in twelve Spanish centers between 2018 and 2020.

RESULTS

268 patients with PA treated by surgery (n = 100) or with MRA (n = 168) were included. At baseline, patients treated with surgery were more commonly women (54.6% vs 41.7%, P = 0.042), had a higher prevalence of hypokalemia (72.2% vs 58%, P = 0.022) and lower prevalence of obesity (37.4% vs 51.3%, P = 0.034) than patients treated with MRA. Adrenalectomy resulted in complete biochemical cure in 94.0% and clinical response in 83.0% (complete response in 41.0% and partial response in 42.0%). After a median follow-up of 23.6 (IQR 9.7-53.8) months, the reduction in blood pressure (BP) after treatment was similar between the group of surgery and MRA, but patients surgically treated reduced the number of antihypertensive pills for BP control more than those medically treated (∆antihypertensives: -1.3 ± 1.3 vs 0.0 ± 1.4, P < 0.0001) and experienced a higher increased in serum potassium levels (∆serum potassium: 0.9 ± 0.7 vs 0.6 ± 0.8mEq/ml, P = 0.003). However, no differences in the risk of the onset of new renal and cardiometabolic comorbidities was observed between the group of surgery and MRA (HR = 0.9 [0.5-1.5], P = 0.659).

CONCLUSION

In patients with PA, MRA and surgery offer a similar short-term cardiovascular protection, but surgery improves biochemical control and reduces pill burden more commonly than MRA, and lead to hypertension cure or improvement in up to 83% of the patients.

Bilateral Adrenalectomy in a Patient With Refractory Primary Aldosteronism Due to Adrenal Hyperplasia

Primary aldosteronism (PA) is a frequent cause of secondary hypertension. The main cause of PA is bilateral adrenal hyperplasia, and treatment is usually medical with mineralocorticoid receptor antagonists (MRAs) such as spironolactone or eplerenone. In this paper, we present a rare clinical case of a middle-aged female with refractory arterial hypertension and hypokalemia that complementary medical tests confirmed PA due to bilateral hyperplasia, and despite a maximum dose of spironolactone and oral potassium supplements, there was no clinical response. Because of this, finally, the patient needed surgical treatment based on bilateral adrenalectomy, which was effective. This is unusual and poorly described in the medical literature.

Diagnosis of primary hyperaldosteronism

Primary aldosteronism (PA) is the most common cause of secondary arterial hypertension. Moreover, it is associated with a higher cardio-metabolic risk than the observed in patients with essential arterial hypertension (EHT). Therefore, a high index of clinical suspicion for PA is mandatory. If an elevated aldosterone/renin ratio is confirmed, confirmatory tests should be performed, with the exception in those patients with florid PA, with, with spontaneous hypokalaemia, plasma aldosterone > 20 ng/dL and suppressed renin, in whom this step would not be strictly necessary. Intravenous saline infusion test or captopril test are the commonly used confirmatory tests. The last step in the diagnosis of PA is the localization study, being the computerized axial tomography (CT) of the adrenal glands the initial test of choice, and adrenal venous sampling (AVS), the definitive localization test in most cases. This review summarizes the available data about the diagnosis of PA, from screening to confirmatory study and localization.

Adrenal vein sampling: technique and protocol, a systematic review

Primary aldosteronism is the leading cause of secondary hypertension worldwide. Its deleterious effects outstrip those due to blood pressure elevation alone. An essential part of the work-up of a patient with primary aldosteronism is determining if aldosterone production is unilateral or bilateral. With the former, surgery offers a potential cure and better overall outcomes. Adrenal vein sampling is considered the most reliable method to determine whether production is unilateral or bilateral. Sampling may be non-diagnostic when the vein cannot be properly cannulated. But with proper knowledge and experience as well as the utilization of certain techniques, procedure success can be high. Multiple protocols exist; their rationale and drawbacks are reviewed here. This article will give the reader an overview of techniques for improving procedural success as well as background, rationale and evidence to guide one in choosing the appropriate procedural and interpretation protocol.

Feasibility of Iodine-131 6β-Methyl-Iodo-19 Norcholesterol (NP-59) Scintigraphy to Complement Adrenal Venous Sampling in Management of Primary Aldosteronism: A Case Series

Purpose

Primary aldosteronism (PA) is mainly comprised of aldosterone-producing adenoma and bilateral idiopathic adrenal hyperplasia. Current guidelines recommend adrenal venous sampling (AVS) as a gold standard method to classify the subtypes. However, because of technical challenges in AVS including invasiveness of AVS and a wide range of success rate for cannulation, it is not uncommon that appropriate decisions could not be made depending on AVS. The aim of this study is to elucidate the proper role of I‑131‑6β‑iodomethyl‑norcholesterol (NP-59) scintigraphy in management of PA.

Patients and Methods

Between January 2009 and October 2018, patients with PA were retrospectively reviewed for the study. Five patients were included in the study who had NP-59 scintigraphy with non-conclusive AVS results or without AVS. We described the clinical outcome of patients in whom clinical decisions were made according to NP-59 scintigraphy results.

Results

Patients in the presenting cases were diagnosed for PA. AVS, the most reliable test to identify unilateral APA, were not applicable because of hypersensitivity to contrast dye (patient 1), and use of antiplatelet agents after acute cerebral infarction (patient 2). NP-59 scintigraphy was performed in patients 3 and 4 whose result of AVS and CT scan were inconsistent. In patient 5, who had bilateral adrenal adenomas (two in the left and one in the right adrenal gland), both unsuccessful catheterization and coexistence of cortisol overproduction made AVS results unreliable.

Conclusion

Based on clinical outcomes of these case series, it is noticeable that NP-59 scintigraphy could play a substantial role in management of PA in selected cases.

Adrenal Incidentaloma

An adrenal incidentaloma is now established as a common endocrine diagnosis that requires a multidisciplinary approach for effective management. The majority of patients can be reassured and discharged, but a personalized approach based upon image analysis, endocrine workup, and clinical symptoms and signs are required in every case. Adrenocortical carcinoma remains a real concern but is restricted to <2% of all cases. Functional adrenal incidentaloma lesions are commoner (but still probably <10% of total) and the greatest challenge remains the diagnosis and optimum management of autonomous cortisol secretion. Modern-day surgery has improved outcomes and novel radiological and urinary biomarkers will improve early detection and patient stratification in future years to come.

131I-6β-iodomethyl-19-norcholesterol adrenal scintigraphy as an alternative to adrenal venous sampling in differentiating aldosterone-producing adenoma from bilateral idiopathic hyperaldosteronism

OBJECTIVE

To assess the correlation value between adrenal venous sampling (AVS) and I-6β-iodomethyl-19-norcholesterol (NP-59) adrenal scintigraphy in differentiating aldosterone-producing adenoma (APA) from bilateral idiopathic hyperaldosteronism (BHA), and the use of NP-59 scintigraphy as an alternative to AVS.

METHODS

Overall, 29 patients with APA or BHA who underwent AVS and dexamethasone-suppression NP-59 scintigraphy were included between 2010 and 2017. The correlation value between AVS and dexamethasone-suppression NP-59 scintigraphy was assessed using each lateralisation index (LIAVS and LI1NP-59). Tumour presence and size were evaluated using computed tomography. The sensitivity and specificity of dexamethasone-suppression NP-59 scintigraphy for APA according to each lateralisation index threshold were calculated.

RESULTS

Of 29 patients, 12 presented with APA and 17 with BHA according to AVS. The correlation value between LIAVS and LI1NP-59 was 0.63 (P < 0.001). If the cut-off points were 2.55 and 1.80 in all cases, the sensitivity and specificity were 0.33 and 1.00 as well as 0.58 and 0.94, respectively. In adrenal microtumours (maximum diameter ≤10 mm), no cases revealed a cut-off point of >1.8. However, in adrenal macrotumours (maximum diameter >10 mm), the cut-off point of 2.55 represented the best compromise (sensitivity: 0.44; specificity: 1.00).

CONCLUSION

NP-59 scintigraphy can be used as an alternative to AVS if there is a strong lateralisation on NP-59 scintigraphy and adrenal macrotumours observed on the computed tomography when AVS is technically challenging, particularly in the right adrenal vein cannulation, and if contraindications, such as allergy to contrast materials and renal failure, are observed.