Secondary hypertension is defined as hypertension with a detectable cause and is one of the clinical manifestations of a disease, most of which is clinically curable. Secondary hypertension with obvious characteristics is easier to identify and less likely to be missed, while atypical secondary hypertension is often misdiagnosed as primary hypertension.
I. Epidemiology of secondary hypertension
At present, the prevalence of hypertension in China is about 18.8%, and the number of patients in the country is about 160 million. In the face of such a large population, it is almost impossible to conduct detailed screening for secondary hypertension in each hypertensive patient, so the proportion of secondary hypertension in the whole hypertensive population cannot be accurately counted.
Second, the differential diagnosis of secondary hypertension
Most secondary hypertension has its own pattern of development to a certain stage, and because of the multidisciplinary and interprofessional characteristics of secondary hypertension, the clinical manifestations are complex and diverse, which requires the hypertension specialist to master the knowledge of cardiology, urology, endocrinology, cranial surgery, thoracic surgery, abdominal surgery, psychiatry and obstetrics and gynecology and other diseases related to secondary hypertension. In addition, medically induced hypertension (such as alcohol, licorice, birth control pills, estrogen) and occupational hypertension should also be given high priority.
(A) adrenal disorders
1.Primary aldosteronism
Typical cases of intractable increase in blood pressure, hypokalemia, increased nocturia, etc.. There are two high and two low manifestations. Patients with glucocorticoid-dependent primary aldosterone have short stature and do not develop normally. Patients with early proaldosteronism or atypical cases may not have any characteristic clinical manifestations.
Primary aldosteronism reaches 10-20% in hypertension and can be as high as 9.5% in normokalemic hypertensive patients. The plasma aldosterone/renin activity ratio is currently used as the initial screening method. Imaging can be used to localize the diagnosis. Adrenal venous blood sampling is one of the important methods for the typological diagnosis of primary aldosteronism and is considered the gold standard for determining the cause of primary aldosteronism, which has not been widely performed in China due to the difficulty of operation
2.Pheochromocytoma
The clinical manifestations of pheochromocytoma are complex, diverse, variable and sudden, which makes the diagnosis very difficult, but about 90% of pheochromocytomas are benign tumors and can be cured after diagnosis, so the clinical differential diagnosis is significant, otherwise serious complications or pheochromocytoma crisis can lead to death.
Some patients may present with a complaint of elevated blood pressure, with a sustainable rise in blood pressure, or with a paroxysmal rise in blood pressure, but with normal blood pressure in the absence of an attack. Typically, elevated blood pressure may be accompanied by palpitations, sweating, dizziness, and headache. The following qualitative and localization tests should be performed in the presence of pheochromocytoma features.
24-hour urinary catecholamines, 3-methoxy-4-hydroxy bitter almond acid, and plasma catecholamines are significantly elevated. Patients with pheochromocytoma with a decrease in blood pressure >35/25 mmHg after 2 minutes of phentolamine injection that lasts more than 5 minutes are considered to have a positive phentolamine test. Imaging can determine the number and location of the tumor. 131-meso-iodobenzylguanidine imaging has higher specificity, sensitivity, and resolution than ultrasound and CT scan, and also has a therapeutic effect on malignant pheochromocytoma.
3 .Cushing’s syndrome
Patients have special body shape such as full moon face, buffalo back, centripetal obesity. Plasma cortisol rhythm disappears, and adrenal imaging may reveal enlarged adrenal glands or tumor-like changes.
Blood cortisol cannot be suppressed in 1mg dexamethasone suppression test and small dose dexamethasone suppression test, while blood cortisol can be suppressed in high dose dexamethasone suppression test; tumor or hyperplasia in adrenal gland or tumor in pituitary gland can be seen in imaging examination.
(B) Secondary hypertension due to renal disorders
1, renal substantial hypertension
It is the most prevalent and difficult to eradicate secondary hypertension, and the clinical features are almost always known, and it is the first secondary hypertension that people think of. Detailed medical history; routine urine and renal function tests are of great value in the diagnosis of renal parenchymal hypertension.
Special examination items such as intravenous pyelogram help in the differential diagnosis. Patients with acute glomerulonephritis are often unremarkable due to a marked decrease in glomerular filtration rate; if it shows delayed excretion of contrast and a reduced bilateral renal shadow, the diagnosis of chronic glomerulonephritis is facilitated.
Intravenous pyelogram in patients with chronic pyelonephritis may show scarring and atrophic changes in the renal pelvis and kidneys.
It should be noted that the symptoms of chronic glomerulonephritis may be insidious, especially when renal failure and bilateral renal shadow narrowing occur, not easily distinguished from hypertensive disease kidney damage, differential diagnosis difficulties can be done in the early kidney biopsy.
2.Reninoma
Although the current data shows that the prevalence of reninoma is not high, it should not be ignored in the differential diagnosis. Untimely diagnosis and treatment may lead to malignant acute hypertension, which can be cured by clear diagnosis. Patients have a young age of onset, mostly under 30 years old, with a short course of hypertension and rapid progression, mostly presenting with malignant hypertension, hypokalemia, and nocturia, but mostly without periodic paralysis.
(C) hypertension due to vascular disorders
1.Aortic constriction
CTA or MRI can show the stenotic part of the aorta, and digital imaging of the aorta can show the location, morphology and the relationship between other surrounding vessels. Current instruments that can measure both the index of the degree of atherosclerosis (PWV) and the index of the degree of luminal stenosis are clinically important in screening for aortic disease.
Features of aortitis or fibromuscular dysplasia: young age of onset, mostly under 30 years old; more common in women than men; no family history of hypertension; short duration and rapid progression of hypertension, mostly presenting with malignant acute hypertensive manifestations; asymmetric blood pressure in the extremities, sometimes showing pulselessness; vascular murmurs can mostly be heard in the head and neck, upper abdomen and low back; mild decrease in blood potassium, mostly between 3.0-3.5 mmol/L. The fundus changes are obvious, progressing rapidly and showing ischemic fundus lesions.
2.Renal vascular hypertension
Medical history of sudden onset of hypertension, especially in young or elderly people, hypertension is malignant, or benign hypertension suddenly aggravated, diastolic blood pressure is moderately or severely elevated and hypertensive patients who do not respond to drug therapy should be suspected of renal vascular hypertension.
About 50% of patients with renal vascular hypertension have vascular murmurs on abdominal auscultation, which are mostly located at 3 cm-7 cm above the umbilicus and on both sides, and sometimes a high-pitched systolic-diastolic or continuous vascular murmur can be heard at the spinal rib angle.
Abdominal ultrasonography: If one side of the kidney is significantly smaller than the opposite side in longitudinal axis, with a diameter difference of 1.5 cm or more, renal vascular hypertension is highly suspected.
Intravenous pyelogram: If one kidney excretes contrast later than the contralateral side, if the kidney outline is irregular or significantly smaller than the contralateral side (diameter difference of 1.5 cm or more), if the contrast density is higher than the contralateral side, or if there are indentations in the upper ureter and renal pelvis (possibly indentations in the enlarged ureteral artery), all suggest the possibility of renal vascular pathology.
Selective renal arteriography remains the current gold standard for confirming renal vascular hypertension. The PRA measurement of the divided renal vein confirms increased renin production in the affected kidney and is important in assessing the function of renal artery stenosis.
As a result of renal artery stenosis, renal blood flow decreases, glomerular parietal cells secrete increased renin, and blood pressure increases, which is a common cause of secondary hypertension.
(iv) Anxiety-depressive hypertension
Anxiety and depressive disorders are now gaining clinical attention and are characterized by diverse symptoms, forcing patients to consult relevant departments because of their complex somatization symptoms.
(V) Obstructive sleep apnea syndrome
Foreign epidemiology shows a strong correlation between sleep apnea syndrome and hypertension, with at least 30% of hypertensive patients having OSAS and 60%-90% of OSAS patients having hypertension. In patients with short neck, nail bed or cyanosis in the mouth and lips, especially obese patients, OSAS should be excluded. Polysomnography sleep monitoring can confirm the diagnosis with more than 30 recurrent episodes of apnea or apnea hypoventilation index ≥ 5 times/hour during 7 hours of sleep per night.