Prospective Study on the Prevalence of Secondary Hypertension among Hypertensive Patients Visiting a General Outpatient Clinic in Japan

Secondary hypertension (SH) including endocrine hypertension has been reported to be uncommon. We estimated the prevalence of SH among hypertensive patients. We prospectively studied 1,020 hypertensive patients. As an initial screening, we measured plasma aldosterone concentration, plasma renin activity, serum cortisol concentration and plasma catecholamine concentration and conducted abdominal ultrasonography (US). As a secondary screening, we performed furosemide plus upright test, captopril renography, dexamethasone suppression test, 24-h urine catecholamine measurement and abdominal CT. Finally, primary aldosteronism with the exception of idiopathic hyperaldosteronism, pheochromocytoma, and Cushing's syndrome were diagnosed by histopathological examination of surgical specimens. Idiopathic hyperaldosteronism was clinically diagnosed by adrenocorticotrophic hormone (ACTH)-stimulated adrenal venous sampling and renovascular hypertension by renal arteriography. There were 61 patients with primary aldosteronism, 5 with renovascular hypertension, 11 with Cushing's syndrome, 10 with preclinical Cushing's syndrome and 6 with pheochromocytoma, and the prevalence of SH was 9.1% among 1,020 hypertensive patients. In 76 (82%) of 93 patients with SH, hypertension was cured or improved after unilateral adrenalectomy, transsphenoidal pituitary adenectomy or percutaneous transluminal angioplasty. With the exception of US and CT, all initial and secondary screening tests were found to be sensitive and specific for differentiating SH from essential hypertension (EH). In conclusion, the measurement of various hormone concentrations was very sensitive for ruling out SH--a condition for which, in the present study, there were few specific signs or symptoms--while CT and US examinations were not always useful for differentiating SH from EH. The prevalence of curable SH among hypertensive subjects was higher in this study, which was conducted by our simple method of screening tests, than in previous reports. Hypertensive patients should be screened for SH and the underlying disease treated appropriately to avoid long-term use of antihypertensive drugs and risks of atherosclerotic complications.