Secondary Hypertension

What is secondary hypertension?

It is hypertension that is secondary to another disease or an identifiable cause. This can be a disease affecting the kidneys, arteries, endocrine system or nervous system. It can also be due to pre-eclampsia that occurs during pregnancy, obstructive sleep apnea, cancer, particular medications and many other causes.

How is secondary hypertension treated?

Secondary hypertension is best treated by controlling the underlying condition. Below, we talk about some of the more common causes of secondary hypertension in more detail and how these can be treated.

Kidney disease

The kidneys are the organs that control the volume of blood in the body and so they play a huge part in controlling blood pressure. If they are disrupted by disease, hypertension can set in. Diseases include:

• Polycystic kidney disease (PKD). This is when there are numerous fluid filled cysts covering the kidneys, causing them to become enlarged. There is no specific treatment that can get rid of the cysts, but blood pressure is controlled with drugs used to treat essential hypertension.
• Chronic glomerulonephritis, a disease where the glomeruli (filtration tubes of the kidneys) or the blood vessels of the kidneys become inflamed, usually in both kidneys. Prednisone, which is a steroid, is used to treat the disease. This in turn leads to lowered blood pressure over time.
• Tumours of the kidney, including pheochromocytoma and juxtaglomerular cell tumours. Pheochromocytomas secrete large amounts of catecholamines such as adrenaline, which cause a rise in blood pressure. Treatment is by surgical removal of the tumour, but until then, hypertension is treated with alpha-blockers. Juxtaglomerular cell tumours are also treated in this way. These tumours secrete renin, which is used by the body to raise blood pressure via the renin-angiotensin system.

Arteries

Problems with the arteries are one of the major causes of secondary hypertension, especially atherosclerosis. This is a condition where the artery wall thickens due to fatty build-ups inside the lumen of the artery, sometimes due to high cholesterol. These can become thickened and coated in calcium (calcified), which makes the arteries rigid instead of flexible.

When this occurs in one of the arteries leading to the kidneys, it is called renal artery stenosis. When someone has this condition, blood can’t flow as easily through the renal arteries, meaning that the blood entering the kidneys is at a lower pressure than in the rest of the body. Baroreceptors (pressure receptors) sense this low pressure and ‘think’ that the whole body is affected by this low pressure so they set up a mechanism to increase the blood pressure of the body. This is done by stimulating renin secretion by the kidney. This results in increased levels of aldosterone and angiotensin II in the blood, which increase blood volume by promoting reabsorption of water and sodium into the blood. Therefore we see hypertension.

How is renovascular disease treated?

• Risk factors that affect blood vessels have to be reduced by measures such as stopping smoking and by lowering cholesterol in the blood by using medication such as statins.
• A stent can be used to keep the artery from blocking. This is a wire mesh tube inserted into the artery to the kidney to improve blood flow.

Endocrine system

The endocrine system is the system in the body that secretes and maintains the correct balance of hormones in the bloodstream and tissues. These include hormones that control our blood pressure.

Cushing’s syndrome

This is a condition where there is an excessive level of cortisol in the blood, either due to taking steroid medication that contains glucocorticoids or because of a tumour that secretes cortisol.  Cortisol is a hormone that is normally secreted by the adrenal glands during stress. It can raise blood pressure by enhancing the constricting effect that adrenaline has on blood vessels.

Most of the time this can be treated by tapering off the medication causing the Cushing’s syndrome. However, if the condition is caused by a cortisol-releasing tumour, surgical removal of the tumour is required.

Hyperthyroidism

Hyperthyroidism occurs when the thyroid gland is overproducing thyroid hormones, such as thyroxin. This is the main hormone produced by the thyroid gland. It acts to speed up the metabolism of the body and can raise blood pressure by increasing the body’s sensitivity to adrenaline.

How is hyperthyroisism treated?

• Thyrostatic drugs can be taken. These are drugs used to inhibit production of thyroid hormones. The most commonly used thyrostatic in the UK is carbimazole

References

 www.patient.co.uk - "Statins and Other Lipid Lowering Drugs"

US National Institute of Health - "Stents"

Klabunde E, Cardiovascular Physiology Concepts "Secondary Hypertension"