The frequency of secondary hypertension

Renovascular Hypertension

Hypertension constitutes a major health problem and the challenge is to identify patients having ‘surgically’ curable renal vascular disease among the majority with so-called essential hypertension. The best of unsatisfactory diagnostic tests are renography and plasma renin activity both before and during angiotensin II blockade. The necessity of better screening tests has increased because of the recent advances in surgical techniques and especially percutaneous transluminal renal angioplasty. The latter has definitely become the method of choice for correction of suspected hemodynamically significant artery stenoses whenever technically feasible. With improved angioplasty techniques the risk of treating renal artery stenosis without hemodynamic and clinical importance (so-called cosmetic repair) has increased. Unfortunately randomized trials including surgery versus angioplasty are not available. It should be kept in mind that only after correction of the stenosis is achieved and the blood pressure has become normal, can the diagnosis of renovascular hypertension be made with certainty.

Current opinions in renovascular hypertension

Renal artery stenosis and renovascular hypertension are important considerations in patients with hypertension that is difficult to control. The diagnosis may also have prognostic significance for progressive renal disease. The most common causes of renal artery stenosis are atherosclerotic disease and fibromuscular dysplasia. The pathophysiology of renal artery stenosis is reviewed, and the pros and cons of various imaging studies in the appropriate clinical setting are discussed. Treatment includes aggressive control of hypertension, dealing with associated cardiac risk factors, and angioplasty or surgery in specific circumstances.

A Longitudinal Study of the Yield and Clinical Utility of a Specifically Designed Secondary Hypertension Investigation Protocol

OBJECTIVE

It has become common practice to use a day-case based approach to identify from the population of hypertensive patients those with an identifiable cause. We aimed to prospectively identify 96 consecutive hypertensive patients undergoing an algorithmic investigation protocol based around two day case hospital attendances.

METHODS

The overall diagnostic yield and associated costs were recorded and the patients were observed for a mean of 2.5 years with ambulatory blood pressure (BP) monitoring every three months.

RESULTS

A secondary cause of hypertension was identified in 18.1% of patients, three quarters of whom had renovascular disease. There was a fall in blood pressure with time (157/97 vs. 140/85) but this was associated with an increase in the amount of medication required (mean medication score 5.99 vs. 7.65). Improvement in BP occurred irrespective of whether or not a secondary cause was identified. Only 3.2% of patients were cured of their hypertension as a result of enrollment in the protocol. The cost of identifying each case of secondary hypertension was Euro 10, 196.

CONCLUSIONS

A comprehensive protocol aimed at identifying secondary hypertension had a low yield, the majority of whom had renovascular disease. In light of recent data illustrating the lack of improvement in BP following dilatation or bypass of atherosclerotic renovascular disease, it is debatable whether searching for it is justifiable.

The prevalence of secondary and curable hypertension

The prevalence of secondary and curable hypertension was studied retrospectively in 1000 patients. The concept of "secondary hypertension" was used when hypertension was combined with a disease which may have affected the individual's blood pressure. When this definition was applied, 47 of the patients displayed some form of secondary hypertension: stenosis of the renal artery in 10, renoparenchymal disease in 21, hydronephrosis in 3, and endocrine hypertension in 13 (8 of the latter were using oral contraceptives). The blood pressure normalized in 11 and improved in 7 of these patients after operative treatment of the underlying disease or, when appropriate, discontinuance of intake of contraceptive pills. The incidence of secondary hypertension in this and other series is low, and the number of patients with curable hypertension is even lower. In the majority of cases, secondary hypertension can be diagnosed by anamnesis, physical examination and simple tests of blood and urine. If this basic investigation can be extended, the incidence of stenosis of the renal artery should be examined in the first place. Hypertension in young patient and in patients who are difficult to treat often justifies a more extensive investigation.

Simple screening procedure for the diagnosis of primary aldosteronism

A simple screening protocol for the diagnosis of primary aldosteronism was applied to 149 hypertensive patients. The diagnostic criterion for possible primary aldosteronism was the combination of supine plasma renin concentration less than 15 mIU/l (normal range 6-54) and plasma aldosterone concentration greater than 11 ng/100 ml (normal range 3-18). None of 63 persistently normokalaemic hypertensive patients fulfilled this criterion. Seventeen (20%) of 86 hypokalaemic patients showed hormonal values consistent with primary aldosteronism. The presence of an adrenal adenoma was verified in eight of these patients. Thus screening for primary aldosteronism can be restricted to hypokalaemic patients. The prevalence of primary aldosteronism in a hypertensive population was calculated to be less than 1%.

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.

[Slight hormonal alterations in a patient with a large pheochromocytoma]

We present a case report that the patient had symptoms suggesting pheochromocytoma, a large tumor (> 50 g) and a single minimally altered laboratorial test, exemplifying a diagnostic pitfall. A 31 y.o. male patient had two acute abdominal events, the last one accompanied by headache, arterial hypertension, facial flushing, perspiration and cutaneous pallor. In another admission, the patient had sustained arterial hypertension and cardiac arrhythmia. From laboratory analysis, the vanililmandelic acid was slightly modified. Scintigraphy disclosed a large adrenal mass suggesting pheochromocytoma. Histopathology confirmed this hypothesis. This report points out that patients with symptoms suggesting pheochromocytoma, even when plasma catecholamines and urinary metanephrines levels are normal, may harbor large tumors with a high catecholamines turnover or that had undergone hemorrhagic necrosis.

An update on renovascular hypertension

Renovascular hypertension (RVH) represents a secondary and potentially remediable form of hypertension. Elevated blood pressure is only one of a broad array of pathophysiologic consequences that are associated with decreased renal perfusion. Our ability to accurately and noninvasively detect stenotic lesions within the renal artery is growing. However, functional assessment of renal parenchyma and hemodynamic significance of renal artery lesions is still limited. Advances in endovascular techniques spurred interest in the concept of ischemic nephropathy and the effect of renal artery revascularization on renal function. Despite the relative frequency of atherosclerotic renal artery stenosis (ARAS), there currently is no consensus on the most appropriate therapy. In this article, we focus on the two most common causes of RVH, ARAS and fibromuscular dysplasia. We discuss the therapeutic strategies, disease mechanisms, clinical findings, evolving trends, and developments.

Forms of mineralocorticoid hypertension

Hypertension with hypokalemia, metabolic alkalosis, and suppressed plasma renin activity defines mineralocorticoid hypertension. Mineralocorticoid hypertension is the consequence of an overactivity of the epithelial sodium channel expressed at the apical membrane of renal cells in the distal nephron. This is usually the case when the mineralocorticoid receptor is activated by its physiologic substrate aldosterone. The best known form of mineralocorticoid hypertension is an aldosterone-producing adrenal tumor leading to primary aldosteronism. Primary aldosteronism can also be caused by unilateral or bilateral adrenal hyperplasia and rarely adrenal carcinoma. Interestingly, most of the inherited monogenic disorders associated with hypertension involve an excessive activation of the mineralocorticoid axis. In some of these disorders, mineralocorticoid hypertension results from activation of the mineralocorticoid receptor by other steroids (cortisol, deoxycorticosterone), by primary activation of the receptor itself, or by constitutive overactivity of the renal epithelial sodium channel. The present review addresses the physiology and significance of the key players of the mineralocorticoid axis, placing emphasis on the conditions leading to mineralocorticoid hypertension.

Influence of antihypertensive medication on aldosterone and renin concentration in the differential diagnosis of essential hypertension and primary aldosteronism

OBJECTIVE

Antihypertensive drugs influence the neurohumoral cardiovascular system and the concentration of hormones involved in blood pressure regulation. Little is known, however, about the extent to which various antihypertensive drugs influence cardiovascular hormone concentrations and thus disturb the differential diagnosis of hypertension in clinical practice. In this study we compare the impact of different antihypertensive medicaments on the renin-angiotensin-aldosterone system in patients with essential hypertension who are screened for primary aldosteronism.

DESIGN AND SUBJECTS

We analysed serum aldosterone (SAC) and plasma renin concentration (PRC) in 37 normotensive controls, 144 hypertensive patients with essential hypertension, and 19 patients with primary aldosteronism. Patients were on different treatment regimens such as single drug or combination therapy with beta-blockers, angiotensin-converting enzyme (ACE) inhibitors or angiotensin II subtype 1 (AT1) receptor antagonists, calcium channel blockers, spironolactone and no treatment.

RESULTS

In patients with essential hypertension, beta-blocker therapy (n = 47) led to a highly significant suppression of renin, whereas serum levels of aldosterone were not significantly altered. ACE inhibitors and AT1 receptor antagonists (n = 55) decreased aldosterone levels only to a minor extent. Calcium channel blockers (n = 23) had no significant influence on SAC or PRC. In patients with primary aldosteronism treated with spironolactone (n = 8), renin escaped suppression and reached very high levels.

CONCLUSION

Beta-blockers and aldosterone antagonists have the strongest impact on the renin-angiotensin system. The decrease in renin concentration by beta-blockers leads to an increase in the ratio of aldosterone to renin, and thus to false-positive results in patients with essential hypertension. Calcium channel blockers, and probably also ACE inhibitors and AT1 receptor antagonists alone or in combination, may be continued during screening for primary aldosteronism by determination of renin and aldosterone concentration.

Is primary aldosteronism underdiagnosed in clinical practice?

1. Primary aldosteronism is a syndrome consisting of hypertension, suppressed renin activity or concentration and high aldosterone levels in plasma or urine. The main steps in diagnosis are the determination of renin and aldosterone levels, the demonstration of renin-aldosterone dissociation and discrimination between idiopathic hyperplasia and Conn's adenoma, with only Conn's adenoma amenable to surgery. 2. Patients with resistant hypertension and/or hypokalaemia should be screened for primary aldosteronism with simple, redundant hormonal tests. The aldosterone to renin ratio is a logical initial screening test, a high ratio demonstrating renin-aldosterone dissociation. Criteria for a high ratio should be determined in each laboratory. 3. In patients with documented primary aldosteronism, computed tomography scan and adrenal vein sampling help to distinguish between idiopathic hyperplasia and Conn's adenoma. 4. Patients with low renin hypertension, idiopathic hyperplasia and Conn's adenoma have overlapping values for plasma concentrations of potassium, renin and aldosterone and the aldosterone to renin ratio. Because primary aldosteronism subtypes are quantitative diseases, the true prevalence of primary aldosteronism cannot be defined. 5. The use of sensitive screening tests (e.g. aldosterone to renin ratio) gives a higher prevalence of diagnosed cases of primary aldosteronism, but not of surgically correctable forms. Therefore, there is no clinical evidence that primary aldosteronism is underdiagnosed. 6. There is a need for tests to predict the postoperative blood pressure outcome of surgery in subjects with Conn's adenoma.

The case for renal revascularization

This report reviews renovascular disease, hypertension and renal parenchymal dysfunction. The primary lesions responsible are discussed as well as the strategies for restoring normal renal perfusion. The natural history studies document progressive impairment of renal perfusion and the consequence of renal dysfunction. Renal revascularization interrupts this pathway by relieving or lessening hypertension and preserving renal function which are the therapeutic options.

Renovascular hypertension: predicting surgical cure with exercise renography

Renal artery stenosis with resultant renovascular hypertension has attracted clinical attention because the disease is potentially curable and because numerous diagnostic and therapeutic modalities compete for clinical acceptance. An exercise-mediated disturbance of renal hippurate transport was recently described, and has been implicated as having a role in nephrogenic fixed hypertension. To predict the final course of renovascular hypertension before operation we carried out a prospective study with the goal of verifying the predictive value of exercise hippurate scintigraphy. The study was to test the hypothesis that patients with disturbance of renal hippurate transport (pathologic renogram) induced by exercise would have stabilized hypertension and would continue to be hypertensive after operation. Thirty-one patients with hypertension who had unilateral or bilateral renovascular stenosis documented on angiography were referred to rest and exercise hippurate scintigrams before operation. The results of the examinations at rest served as standard and were compared with the exercise scintigrams. In 19 of the 31 (61%) patients a disturbance of transrenal hippurate transport evolved during exercise, whereas 12 (39%) patients failed to respond to exercise with altered hippurate kinetics. Twenty-six patients went on to renovascular operations; five had percutaneous transluminal angioplasty. Revascularization results differed markedly when the blood pressure response of patients with positive results on exercise (abnormal) and patients with negative results on exercise (normal) were compared. Ten of 12 patients with hypertension who had normal exercise renograms were cured. In comparison, blood pressure values were little influenced by therapy in patients with an abnormal response, where 17 of 19 patients continued to have hypertensive disease after therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

The angiographic incidence of renal artery stenosis in the arteriosclerotic population

The incidence of renal artery stenosis was evaluated with intra-arterial digital subtraction angiography in 100 consecutive patients referred for peripheral arteriopathy. Fifty-seven patients were normotensive, 43 were hypertensive. In the normotensive group, renal artery stenosis was found in ten patients (17.5%). In the hypertensive group renal artery stenosis was found in twelve patients (28%). It is concluded that the incidence of renal artery stenosis is high in an arteriosclerotic population both in normotensive and hypertensive patients.

[Status of the captopril test in the diagnosis of hypertension]

The place of captopril (C) testing in the screening for renovascular hypertension is still controversial. Baseline and C-stimulated plasma renin concentrations (PRC) were measured in 113 hypertensives, who where referred for the exclusion of secondary hypertension. In addition intravenous digital subtraction angiography (DSA) and a renal scintigraphy were performed. When renal artery disease was revealed by DSA or renin was stimulated the renal arteries were visualized by direct arteriography (and treated by angioplasty if possible). 86 patients underwent each diagnostic test: 21% had renovascular hypertension. Unilateral renal artery stenosis (n = 10) was detected by the captopril test (cutoff values: baseline greater than 40 microU/ml, after C greater than 180 microU/ml, sensitivity 100%). Bilateral renal artery stenosis (n = 8) was missed when the disease was equally severe on either side (sensitivity 50%). The specificity of C testing was 82%, overall sensitivity (uni- and bilateral disease 78%, prevalence 21%, predictive value of the positive test 0.56, predictive value of the negative test 0.93). With i.v.-DSA the renal arteries were technically evaluable in 91% (82/92) of cases. The sensitivity for the detection of all renal artery stenoses was 79% (uni-lateral 100%, bilateral 40%, specificity 97%). The sensitivity of renal scintigraphy for the detection of unilateral renal artery stenoses was 50%, for the detection of bilateral renal artery stenoses 43%, specificity 81%. The present study demonstrates the usefulness of captopril for the detection of unilateral renal artery stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal angiography may be used primarily in the diagnosis of renovascular hypertension

Three hundred and twenty consecutive patients with hypertension were referred to examination with intravenous urography. Only 2 of the 320 urograms performed showed abnormalities possibly related to hypertension. Renal angiography was performed in 39 (12%) of the patients. Seventeen (7%) subjects had renal artery stenosis, of whom 8 (2.5%) were referred to surgery. Four became normotensive and the other 4 had a more treatable hypertension. Urography is an expensive and insensitive method for evaluation of patients with hypertension and should be abandoned. Proper treatment of renovascular hypertension demands the performance of renal angiography. We therefore suggest a program for primary use of renal angiography in the examination of patients with suspected renovascular hypertension.

Surgical management of primary aldosteronism (Conn's syndrome), a correctable cause of hypertension

Clinical, operative and pathological findings in a series of 18 patients with aldosterone producing adrenal cortical adenomas are reviewed. All patients presented with hypertension and hypokalaemia. The main challenges in preoperative diagnosis were to differentiate primary aldosteronism from other causes of hypokalaemia, such as diuretic therapy, to establish the presence of a discrete adenoma and to localize the tumour to the left or right adrenal gland. A high rate of success was achieved in predicting a surgical diagnosis of aldosterone-producing adenoma. This was attributed to thorough biochemical evaluation of the underlying metabolic state by measurement of renal potassium handling and by determining the responses of the renin-aldosterone axis to changes in sodium balance. Preoperative tumour localization, using adrenal phlebography or scintiscanning, was accomplished in only eight cases. Our experience suggests that the transabdominal approach is preferable for cases in which a unilateral lesion is not clearly identified by imaging techniques.

Results of intravenous digital subtraction angiography (IVDSA) as a screening method for renovascular hypertension

Since January 1982 we have combined urography in hypertensive patients with intravenous angiography of the renal arteries. In more than 80% of 163 patients the examination was of good diagnostic quality and both renal arteries were well visualised. IVDSA has a lower morbidity and cost than conventional angiography. It is more accurate than urography and therefore offers better screening of a selected group of hypertensive patients.

The hunt for renal hypertension

The proportion of cases of hypertension with a renal cause which can be corrected by surgery is very small. Radiological diagnosis of such a cause is expensive and time-consuming; hence the rewards of intensive investigation are small compared with the cost. Measurement of plasma-renin offers a good method of selecting those patients who require further investigation, if the cut-off point is carefully considered in the light of the acceptable incidence of false-positive and false-negative results.