Hypertension: Secondary Causes
If you have high blood pressure (hypertension) there are about nine chances out of 10 that it will be essential hypertension or primary hypertension, which implies that you do not have any clear cause for it. Likely, your hypertension is the outcome of your genes that you have inherited and the lifestyle that you have followed (your salt intake, diet, weight, exercise, smoking, stress, alcohol intake, etc.). This is described in detail under the following patient handouts: Instructions for a Healthy Diet to Help Lower Your Blood Pressure and to Prevent Cardiovascular Disease: The DASH Diet and Dietary Salt Restriction.
You have about one chance in 10 that your hypertension has a specific cause, termed secondary hypertension. Sometimes the underlying cause can be corrected and the hypertension improved or even cured. Secondary causes of hypertension are generally due to problems with the kidneys or with specific endocrine glands that secrete hormones into the bloodstream.
Kidney disease is usually accompanied by high blood pressure. Kidney disease is suggested if you have a raised blood urea nitrogen (BUN) or blood creatinine (Cr), or your kidneys are leaking protein into your urine. However, special types of kidney problems can lead to high blood pressure even in the absence of a raised BUN or creatinine or any abnormality in the urine test. These are conditions that cause a narrowing of the artery to your kidney and a decrease in its perfusion with blood, renovascular hypertension. About one patient in 20 with high blood pressure has renovascular hypertension as the underlying cause.
There are two conditions that can lead to a narrowing of the artery to the kidney and give rise to renovascular hypertension. One is termed fibromuscular dysplasia, which, although uncommon, is found especially in young women. The second cause of a narrowed renal artery is atherosclerotic renal artery stenosis, or hardening of the artery to one or both kidneys. This usually occurs later in life.
Occasionally, the narrowed artery can be detected sufficiently early that there is little damage to the kidney. Correction of the narrowed artery can reduce or even cure the high blood pressure. Unfortunately, the condition usually becomes apparent only after the kidney has been damaged and is shrunken. At that stage, the options for treatment are reduced. Nevertheless, your physician may consider a plan with you to correct the narrowed artery to the kidney if your kidney function deteriorates despite control of your blood pressure. An intervention to correct a narrowed artery usually takes the form of an angioplasty and stent. It is usually undertaken by an interventional radiologist or a vascular surgeon. They will discuss the procedure with you. It entails a full day in the hospital where a needle is inserted under local anesthetic into an artery in your groin, and a catheter is pushed through the needle up into the aorta, to the level of your kidneys. Dye is injected through the catheter to examine the narrowed segment of the artery. A balloon may be inflated on the tip of the catheter to enlarge the artery in a process called angioplasty, and kept open with a stent, which is a metal device that springs open within the artery to hold the wall open.
Unfortunately, this procedure carries some risk of contrast-induced neuropathy, which is kidney damage from the dye. This is more frequent in patients who already have kidney damage and have diabetes. A second complication is atheroembolism, which is caused by the dislodging of some of the hardened artery material from the inside of your aorta during the procedure. This material can float downstream in your blood and wedge in the small blood vessels to your feet, leading to damage of the skin of the toes or to the small vessels of your kidneys, leading to loss of kidney function. Overall, the risk that you may develop a significant degree of contrast-induced nephropathy is less than one in 25, if you do not have kidney failure or diabetes. The risk that you may develop atheroembolism is less than one in 50.
Other causes of secondary hypertension relates to glandular (endocrine) abnormalities. The most important is an excessive secretion of a hormone called aldosterone from one or both of your adrenal glands. You have an adrenal gland on top of each of wach of your kidneys. If you have high blood pressure, you have about one chance in 20 that it is caused by an excessive secretion of aldosterone into your blood.
There are two major causes of an excess of aldosterone secretion. Both cause an increase in blood pressure and an excessive loss of potassium in the urine which can give rise to low blood potassium. If both adrenal glands are overactive, this is treated by drugs that block aldosterone that include spironolactone [Aldactone] or eplerenone [Inspra]. The second cause is a benign tumor of the adrenal glands. This tumor can sometimes be detected by the radiologist from a CAT scan and removed by a surgeon using a laparoscopic procedure. This usually improves the blood pressure. A benign adrenal tumor is the cause of high blood pressure in only about five patients in every 100.
A number of other hormonal conditions can cause secondary hypertension. They are relatively uncommon, and therefore will not be discussed further in this overview.
For further information about secondary hypertension, please review Wilcox. C.S. and Tisher, C. C.: Handbook of Nephrology and Hypertension, Sixth Edition.
For a more detailed discussion on the treatment of different forms of secondary hypertension, please see Wilcox, C.S.: Therapy in Nephrology and Hypertension, Third Edition
Both of these books are available for loan to patients in the Division of Nephrology and Hypertension. The office is on the sixth floor of the Pasquerilla Health Care Building in Georgetown University Medical Center. Please remember to return these books within two weeks so that they will be available for other patients to borrow.
This handout was prepared by Christopher S Wilcox MD, Ph.D.