Primary aldosteronism: diagnosis and noninvasive lateralization procedures

Primary Aldosteronism: Changing Definitions and New Concepts of Physiology and Pathophysiology Both Inside and Outside the Kidney

In the 60 years that have passed since the discovery of the mineralocorticoid hormone aldosterone, much has been learned about its synthesis (both adrenal and extra-adrenal), regulation (by renin-angiotensin II, potassium, adrenocorticotrophin, and other factors), and effects (on both epithelial and nonepithelial tissues). Once thought to be rare, primary aldosteronism (PA, in which aldosterone secretion by the adrenal is excessive and autonomous of its principal regulator, angiotensin II) is now known to be the most common specifically treatable and potentially curable form of hypertension, with most patients lacking the clinical feature of hypokalemia, the presence of which was previously considered to be necessary to warrant further efforts towards confirming a diagnosis of PA. This, and the appreciation that aldosterone excess leads to adverse cardiovascular, renal, central nervous, and psychological effects, that are at least partly independent of its effects on blood pressure, have had a profound influence on raising clinical and research interest in PA. Such research on patients with PA has, in turn, furthered knowledge regarding aldosterone synthesis, regulation, and effects. This review summarizes current progress in our understanding of the physiology of aldosterone, and towards defining the causes (including genetic bases), epidemiology, outcomes, and clinical approaches to diagnostic workup (including screening, diagnostic confirmation, and subtype differentiation) and treatment of PA.

Evaluation of primary aldosteronism

PURPOSE OF REVIEW

The purpose of this review is to briefly summarize current knowledge on diagnosis and treatment of primary aldosteronism, the most frequent cause of endocrine hypertension.

RECENT FINDINGS

The prevalence of primary aldosteronism increases with the severity of hypertension, from 2% in patients with grade 1 hypertension to 20% among resistant hypertensives. The detection of primary aldosteronism is of particular importance, not only because it provides an opportunity for a targeted treatment but also because it has been extensively demonstrated that patients affected by primary aldosteronism are more prone to cardiovascular events and target organ damage than patients with essential hypertension. The diagnosis of primary aldosteronism is a three-step process; screening, confirmation and subtype diagnosis.

SUMMARY

We review, the strategies to correctly identify primary aldosteronism, highlighting the central role of the new guidelines and the diagnostic aspects still under debate.

Aldosteronomas--state of the art

Primary aldosteronism (PA) is the most common cause of secondary hypertension in nonsmokers. Widespread screening of unselected hypertensives has identified PA in as many as 15% of patients. With such screening efforts using the PAC/PRA ratio and PAC, the widespread prevalence of the disease has become apparent while the relative percentage of APA has decreased. PA is confirmed by demonstrating lack of aldosterone suppressibility with sodium loading. Subtype evaluation is best achieved with high resolution CT scanning and AVS in the appropriate setting. In patients with PA and a unilateral source of aldosterone excess, laparoscopic adrenalectomy is the treatment of choice with excellent outcomes and low morbidity as compared with older open approaches. Patients with IHA, or those not amenable or agreeable to surgery, are best managed with a MR antagonist.

Clinical Use of Laboratory Tests for the Identification of Secondary Forms of Arterial Hypertension

The prevalence of secondary hypertension can be underestimated if appropriate tests are not performed. The importance of selecting patients with a high pre-test probability of secondary forms of hypertension is first discussed. The laboratory tests currently used for seeking a cause of hypertension are critically reviewed, with emphasis on their operative features and limitations. Strategies to identify primary aldosteronism, the most frequent form of secondary hypertension, and to determine its unilateral or bilateral causes are described. Treatment entails adrenalectomy in unilateral forms, and mineralocorticoid receptor blockade in bilateral forms. Renovascular hypertension is also a common, curable form of hypertension, that should be identified as early as possible to avoid the onset of cardiovascular target organ damage. The tests for its confirmation or exclusion are discussed. The various tests available for the diagnosis of pheochromocytoma, which is much rarer than the above but extremely important to identify, are also described, with emphasis on recent developments in genetic testing. Finally, the tests for diagnosing some rarer monogenic forms and other renal and endocrine causes of arterial hypertension are explored.

Diagnosis and management of primary aldosteronism

PURPOSE OF REVIEW

To illustrate the steps for clinical management of primary aldosteronism from screening evaluation to surgical and/or medical treatment.

RECENT FINDINGS

It is now widely accepted that primary aldosteronism represents the most common form of endocrine hypertension and its early diagnosis is crucial for hypertensive patients who can be cured by the surgical removal of an aldosterone-secreting adenoma or benefit from a specific medical treatment with mineralocorticoid receptor antagonists. Recent evidence indicates that hyperaldosteronism is indeed associated with detrimental consequences on cardiovascular system, renal function and glucose metabolism.

SUMMARY

The diagnostic protocol for primary aldosteronism requires multistep evaluation and should begin with a screening test, followed when appropriate, by confirmatory test and functional and anatomical evaluation. Finally, although it is technically difficult and the cut-off levels for acceptance of the success are not standardized, the subtype forms should be identified using a selective adrenal venous sampling.

Primary aldosteronism, a major form of low renin hypertension: from screening to diagnosis

There is general consensus on the use of (but not cut-off values for) the aldosterone/plasma renin activity ratio as a screening test for primary aldosteronism. There is also agreement on the need for subsequent confirmatory testing, but not on the protocols to be chosen. The four most common confirmatory tests in clinical practice are oral sodium loading, intravenous saline infusion, captopril challenge and fludrocortisone administration plus sodium loading. The choice of test reflects multiple variables: patient factors (including accessibility, compliance and safety), established practice and cost. Finally, subtype forms and lateralization of aldosterone production should be established by bilateral adrenal venous sampling, despite its technical difficulty and varying criteria for success.

New concepts in adrenal vein sampling for aldosterone in the diagnosis of primary aldosteronism

Improved diagnostic techniques and adoption of a systematic and thorough diagnostic workup can lead to identification of the surgically correctable forms of primary aldosteronism (PA) far more frequently than expected. Adrenalectomy can provide long-term normalization of blood pressure and correction of PA in most patients with an aldosterone-producing adenoma. Forms needing surgical correction are generally held to be less common than forms requiring medical therapy; however, this can be a misconception arising from the lack of systematic use of adrenal vein sampling (AVS). Currently AVS still remains the "gold standard" for identifying unilateral causes of PA that are surgically curable. The criteria for selecting patients to undergo AVS, the technique for performing AVS, and the criteria for analyzing and interpreting its results are summarized here.

Surgically correctable hypertension caused by primary aldosteronism

Surgically correctable forms of primary aldosteronism are generally held to be less common than forms requiring medical therapy. However, with the availability of improved diagnostic techniques and the adoption of a systematic and thorough diagnostic work-up they can be identified more commonly than expected. Adrenal vein sampling (AVS) for measurement of cortisol and aldosterone has emerged as the 'gold standard' diagnostic test for identifying unilateral causes of primary aldosteronism that are amenable to surgical cure. Adrenalectomy can provide long-term normalisation of blood pressure and correction of primary aldosteronism in about 55% of patients with an aldosterone-producing adenoma and can markedly ameliorate blood pressure control in the rest. This chapter summarises the diagnostic work-up suggested for identifying these forms and examines the other diseases mimicking mineralocorticoid excess that enter into the differential diagnosis of surgically curable primary aldosteronism.

Diagnosis of primary aldosteronism: from screening to subtype differentiation

Numerous studies conducted in recent years have reported an increase in the prevalence of primary aldosteronism (PA). This increase has arisen because of changes in our screening methods used to detect PA, notably the widespread use of the ratio of plasma aldosterone concentration to plasma renin activity. A positive screening result, however, is not diagnostic and requires a confirmatory test. Strategies for screening and confirmation of PA and the techniques to identify the two main subtypes of PA--aldosterone-producing adenoma (APA) and bilateral adrenal hyperplasia (BAH)--are particularly important because hypertension in APA can be cured by adrenalectomy, whereas individuals affected with BAH can receive targeted medical treatment with mineralocorticoid receptor antagonists.

Conn’s syndrome (primary hyperaldosteronism) simulating polymyositis

A 44-year-old woman presented with typical polymyositis findings associated with hypokalemia. Abdominal CT as well as plasma renin and aldosterone levels showed a right surrenal adenoma secreting aldosterone. Unilateral adrenalectomy was performed and resolved all the clinical and laboratory manifestations. Hypokalemia should be considered in the differential diagnosis of polymyositis, even in the face of inflammatory cell infiltration in the muscle biopsy.

Primary aldosteronism

Approaching the fiftieth year since its original description, primary aldosteronism is now thought to be the commonest potentially curable and specifically treatable form of hypertension. Correct identification of patients with primary aldosteronism requires that the effects of time of day, posture, dietary sodium intake, potassium levels and medications on levels of aldosterone and renin be carefully considered. Accurate elucidation of the subtype is essential for optimal treatment, and adrenal venous sampling is the only reliable means of differentiating aldosterone-producing adenoma from bilateral adrenal hyperplasia. With genetic testing already available for one inherited form, making more cumbersome biochemical testing for that subtype virtually obsolete and bringing about improvements in treatment approach, an intense search is underway for genetic mutations causing other, more common familial varieties of primary aldosteronism.

Primary aldosteronism: are we diagnosing and operating on too few patients?

Many cases of potentially curable primary aldosteronism are currently likely to be diagnosed as essential hypertension unless screening tests based on suppression of renin are carried out in all hypertensive patients. More than half of the patients with primary aldosteronism detected in this way have normal circulating potassium levels, so measurement of potassium is not enough to exclude primary aldosteronism. When primary aldosteronism is diagnosed, fewer than one-third of patients are suitable for surgery as initial treatment, but this still represents a significant percentage of hypertensive patients. After excluding glucocorticoid-suppressible primary aldosteronism, adrenal venous sampling is essential to detect unilateral production of aldosterone and diagnose angiotensin-responsive aldosterone-producing adenoma. One cannot rely on the computed tomography scan. If all hypertensive patients are screened for primary aldosteronism and the workup is continued methodically in those with a positive screening test, patients with unilateral overproduction of aldosterone who potentially can be cured surgically are not denied the possibility of cure.

Bilateral aldosterone-producing adenomas in two patients diagnosed by immunohistochemical analysis of steroidogenic enzymes

Bilateral adrenal aldosterone-producing adenomas (APA) are rare. It is important to distinguish bilateral APA from idiopathic hyperaldosteronism (IHA) which is due to bilateral hyperplasia of the adrenal cortex. We present two patients with bilateral APA in whom the diagnosis was made histochemically by analyzing steroidogenic enzymes. They showed hypokalemia, high plasma aldosterone concentration (PAC) and suppressed plasma renin activity (PRA). Bilateral adrenal tumors were represented by computed tomography, and surgical resection was performed. In both cases, cytochrome P-450 and other enzymes that were involved in aldosterone synthesis were found mainly in tumor, but little in the zona glomerulosa of the adjacent adrenals, which showed paradoxical hyperplasia. Such cases are difficult to distinguish from IHA. The two disorders were differentiated by immunohistochemical analysis of steroidogenic enzymes.

Primary aldosteronism: difference in clinical presentation and long-term follow-up between adenoma and bilateral hyperplasia of the adrenal glands

Since 1974 primary aldosteronism has been diagnosed in 71 patients in our outpatient clinic. Thirty-four patients had a unilateral aldosterone-producing adenoma, whereas bilateral adrenal hyperplasia was diagnosed in 37 patients. Although at the time of diagnosis the mean potassium values were lower and mean aldosterone levels were higher in patients with an adenoma, as compared to those with bilateral hyperplasia, these laboratory data did not allow us to differentiate between the two leading causes of primary aldosteronism in the individual patient due to pronounced overlap of laboratory values between the two groups. During the first few years, a successful differential diagnosis was made by adrenal phlebography and separate sampling of plasma aldosterone in both adrenal veins; later non-invasive imaging techniques such as computed tomography and radionuclide scanning were used. The best results were obtained in patients with adenoma who underwent adrenalectomy. Fifty-six percent of these patients were clinically and biochemically cured; 28% were improved and had normal blood pressure values during drug treatment. In contrast, patients with bilateral hyperplasia were treated pharmacologically, but only in half of the patients could normal blood pressure values be achieved. Two thirds of the male patients developed gynecomastia during spironolactone treatment. As expected, unilateral adrenalectomy was unsuccessful in the 7 patients with bilateral hyperplasia who underwent surgery. Our results confirm that surgical treatment of adrenal adenomas and drug treatment of bilateral hyperplasias are the appropriate therapy in primary aldosteronism. A differential diagnosis cannot be made on the basis of clinical and non-invasive laboratory data alone; imaging techniques have to be included in the diagnostic process.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of diagnostic tests in the differential diagnosis of primary aldosteronism: unilateral adenoma versus bilateral micronodular hyperplasia

Effective management of primary aldosteronism is dependent upon correct localization of excessive aldosterone production. We report our results of localization studies in patients with biochemically and pathologically confirmed primary aldosteronism. Retrospective chart review identified 69 patients with unilateral adrenal adenoma and 11 with adrenal hyperplasia. Correct unilateral versus bilateral localization of excessive aldosterone production was predicted in 70% versus 71%, respectively, by adrenal venography, 100% versus 63% by adrenal vein hormone sampling, 46% versus 56% by adrenal nuclear scanning and 69% versus 13% by anomalous postural decline of aldosterone. Adrenal computerized tomography appeared to localize correctly 86% versus 80% of the lesions. Unilateral adrenalectomy normalized blood pressure in 79% of the patients with unilateral adenomas versus only 18% of those with adrenal hyperplasia. Once primary aldosteronism is confirmed, localization by adrenal vein sampling, adrenal venography and adrenal computerized tomography is most effective in directing antihypertensive therapy.

Laparoscopic adrenalectomy: the initial 3 cases

Laparoscopic adrenalectomy was performed on 3 patients with primary aldosteronism. Traction with 2 steel skewers placed subcutaneously over the costal arch was combined with conventional intraperitoneal carbon dioxide gas insufflation. This combination provided a good operative field at 8 mm. Hg insufflation pressure. The laparoscopic approach to the adrenal gland requires neither a large skin and muscle incision nor resection of rib(s), and offers lower morbidity and rapid convalescence. Laparoscopic adrenalectomy is a new minimally invasive operation for the treatment of adrenal adenoma.

Bilateral adrenal tumours in primary aldosteronism: localization of a unilateral aldosteronoma by dexamethasone suppression scan

In a patient with primary aldosteronism, in which the postural endocrine tests suggested the presence of an aldosteronoma rather than hyperplasia, bilateral adrenal tumours were found by computer tomography. Adrenal scintigraphy using 6-131I-iodomethyl-19-norcholesterol (NP59) during dexamethasone suppression showed early unilateral adrenal visualization on the left side. After removal of the left adrenal gland, which contained a 2 x 2 x 2 cm adenoma, the blood pressure and aldosterone levels returned to normal. A CT-scan, performed 1 year after the pre-operative CT-scan, showed no change in size of the right adrenal tumour, consistent with a non-functioning adenoma. In this patient, the NP59 scan adequately distinguished a non-functioning from an aldosterone-producing adrenal tumour.

Primary aldosteronism: diagnosis and treatment

The syndrome of primary aldosteronism produces few signs or symptoms. The diagnosis should be suspected when either spontaneous hypokalemia or easily provoked hypokalemia is found in a patient with hypertension. Hypokalemia in association with inappropriate kaliuresis, low plasma renin activity, and a high plasma aldosterone concentration/plasma renin activity ratio are the findings on initial screening tests that should suggest primary aldosteronism. The diagnosis must be confirmed by demonstrating nonsuppressible aldosterone excretion in conjunction with normal cortisol excretion. The choice of therapy is based on distinguishing unilateral from bilateral adrenal disease. With a unilateral adrenal adenoma, surgical removal reverses the hypokalemia and frequently cures the hypertension. In most patients with bilateral adrenal hyperplasia who are treated surgically, however, hypertension persists; thus, the initial treatment in these patients should be pharmacologic.

Possible association of aldosterone producing adenoma and non-functioning adrenal tumor

A 37-year-old woman presented with hyperaldosteronism, suppressed renin levels, and a left adrenal mass on CT scanning. Selective adrenal venous sampling indicated a marked rise of the aldosterone level in the right adrenal vein, while the level in the left vein was low. On laparotomy, an aldosterone producing adenoma (APA) of 12x10x5 mm in size was found in the right adrenal gland and was resected, while the left mass was left in situ. The post-operative course showed normalization of both the clinical and biochemical features of primary aldosteronism, with no sign of recurrence or of enlargement of the remaining adrenal mass in 2.5 years of follow up, suggesting the possible coexistence of a "non-functioning" tumor. This case demonstrates the importance of adrenal venous sampling for the localization of APA particularly since the presence of the APA may be masked by a visualized but unrelated adrenal mass.

Primary hyperaldosteronism

Primary hyperaldosteronism is a challenging diagnosis because of its low incidence and variable pathophysiology. Serum potassium, properly done, is the routine screening test, but is not without its limitations. Confirmation of the diagnosis requires demonstration of abnormally high and nonsuppressible values for aldosterone in plasma and urine and low plasma renin activity. Sophisticated biochemical profiling and localization procedures often are required to identify those subtypes that will benefit from surgical management, including aldosterone-producing adenomas, primary adrenal hyperplasia, unilateral hyperplasia, and aldosterone-producing renin responsive adenomas. Glucocorticoid-suppressible hyperaldosteronism and isolated aldosterone-producing adrenal carcinoma are rare additional subtypes to be identified. Differentiation among these subtypes is a developing process that can be expected to continue to improve with new techniques and new understanding of underlying pathophysiology.