What is secondary hypertension?

What is secondary hypertension?

Hypertension is high blood pressure. Blood pressure secondary to some other disease is called secondary hypertension. Hypertension without any other known cause is called primary hypertension or essential hypertension. Usual hypertension which we hear of in adults is primary hypertension. But hypertension in children, though rare, is most often secondary. In fact it is mentioned that secondary hypertension is more common in the extremes of age.

There are several causes for secondary hypertension which have to be excluded before we can conclude that hypertension is primary. Hence it is customary to test for secondary hypertension whenever high blood pressure is detected. The extent to which testing is done depends on the age and associated conditions. Younger the age, more extensive the testing usually. This is because finding out a potentially curable secondary cause may avoid lifelong medications. On the contrary, missing such a condition early may mean a lost opportunity of total cure for hypertension in that individual.

One of the important causes of secondary hypertension is kidney disease. In children, the usual cause for secondary hypertension is during an episode of transient kidney disease following a bacterial infection. That disease usually has associated decrease in urine output and consequent retention of fluid in the body. They can develop swelling of feet and puffiness of face due to the extra fluid in the body. In severe cases, fluid may collect in the lungs and cause breathlessness. This condition can be diagnosed by appropriate urine and blood tests to assess the function of the kidneys.

Chronic kidney disease is another important cause of secondary hypertension both in children and adults. Hence assessment of the status of kidneys is routinely done in every person with high blood pressure. In addition to blood tests and urine analysis, an ultrasound study of the kidneys, urine tubes and urinary bladder are useful in excluding structural abnormalities. Sometimes an obstruction to the flow of urine from the kidneys like stones may be found, removal of which will improve kidney function.

Narrowing of the blood vessels supplying oxygenated blood to the kidneys (renal artery stenosis) is another remediable cause for secondary hypertension. Renal artery stenosis can occur one side or both sides. Significant renal artery stenosis can be treated by surgical repair or by balloon angioplasty with stent insertion. Long standing renal artery stenosis will damage the kidneys causing kidney failure which will worsen the hypertension.

Diseases of adrenal glands situated just above the kidneys are also an important cause of secondary hypertension. Certain hormones produced by the adrenal glands can increase the blood pressure. This can occur just by excessive function of hormone producing cells of the adrenal glands or by tumours of the adrenal gland. Both these conditions may be rectified by surgery leading to total cure of the high blood pressure.

Excessive production of hormones of the thyroid gland and parathyroid glands located in the neck can also produce secondary hypertension. Increased function of thyroid glands is associated with a fast heart rate and a bounding pulse and a warm body. The condition can be documented by blood tests showing increased thyroid function. Many of them have visible enlargement of the thyroid gland in front of the neck. Parathyroid glands are not visible externally and increase in their function is often mistaken for other conditions like bone disease or kidney stone disease. Function of the parathyroid glands can also be checked by blood tests.

Another important treatable cause of high blood pressure is an obstruction to the aorta known as coarctation of aorta. Aorta is the largest blood vessel carrying oxygenated blood to the whole body. Obstruction usually occurs in the upper part of the aorta as a birth defect. This produces high blood pressure in the arms and low blood pressure in the legs. Importance of checking blood pressure in the legs during initial evaluation for high blood pressure is mainly to rule out this treatable cause for hypertension.

Obstructive sleep apnea (OSA) or obstruction of air passages during sleep is another important cause of secondary hypertension. They have snoring, disturbed sleep at night and consequent day time sleepiness. Obstructive sleep apnea can be diagnosed by a sleep study. There are several surgical and non-surgical treatment options for sleep apnea. Weight reduction is an important modality of treatment of obstructive sleep apnea as it is often associated with obesity. Continuous positive airway pressure (CPAP) machine is very useful in treating OSA.

There is a long list of medications taken for other diseases which can increase the blood pressure. Hormonal birth control pills, non-steroidal anti-inflammatory drugs (pain killers), , antidepressants, and nasal decongestants are some of them. But this cause is usually evident without further tests. Secondary hypertension should also be considered when there is difficulty in controlling high blood pressure.