Brief overview of hypertension

Hypertension, or high blood pressure, is a major health issue that affects people of all ages, although it is more prevalent among adults and the elderly. Hypertension occurs when the force of blood against the walls of the blood vessels (arteries) is too high. Although most people will not feel specific symptoms, high blood pressure can bring about numerous complications if not treated.¹

Your blood pressure is measured by two variables: systolic and diastolic pressure. The systolic pressure (the higher number) reflects the force when your heart pumps blood, while the diastolic pressure (the lower number) is the force in your arteries when your heart is at rest between beats.

Blood pressure should ideally be between 90/60 mmHg and 120/80 mmHg. If your blood pressure is consistently elevated above 140/90 mmHg (or 130/80 mmHg in other guidelines), it is a sign of hypertension.^1,2 

A wide range of risk factors contribute to high blood pressure, including age, family history, and lifestyle habits. These factors are mainly linked to primary hypertension, also known as essential hypertension, where the cause is not entirely clear.³

However, there is another type of high blood pressure where the cause is clear. This is called secondary hypertension. It occurs when your blood pressure is elevated due to certain underlying conditions, such as kidney disease, hormonal problems, or medications. This article focuses on secondary hypertension.

Causes of secondary hypertension

Renovascular hypertension

One of the most prevalent causes of secondary hypertension is renovascular hypertension. It is triggered by the narrowing or blockage of the renal arteries, which supply blood to the kidneys. When this occurs, blood flow to the kidneys decreases, prompting the release of a hormone called renin to regulate blood pressure. Renin then stimulates the release of other hormones, such as angiotensin and aldosterone, leading to an increase in blood pressure. Renovascular hypertension is frequently associated with conditions like renal artery stenosis, fibromuscular dysplasia, and renal artery dissection.^4,5

Renal diseases

Secondary hypertension can be caused by renal diseases such as renal parenchymal hypertension, polycystic kidney disease, glomerulonephritis, chronic pyelonephritis, congenital abnormalities, and many more.⁶ 

Endocrine hypertension

When discussing blood pressure, the endocrine system plays a crucial role. Several hormones have specific roles in blood pressure regulation. For example, aldosterone, produced by the adrenal gland, helps retain sodium (salt) and water, which can elevate blood pressure. Adrenaline, also known as epinephrine, is released during stress, resulting in increased heart rate and blood pressure. Thyroid hormones, produced by the thyroid gland, influence body metabolism and heart rate, indirectly affecting blood pressure.

A group of endocrine diseases, such as Cushing’s syndrome, primary aldosteronism, hypo/hyperthyroidism, and phaeochromocytoma (an adrenal gland tumour), are the most common causes of endocrine hypertension. These conditions generally occur due to excessive hormone secretion caused by gland enlargement, tumours, or other issues.^6,8,9

Vascular disorders

One of the most common vascular disorders that cause secondary hypertension is coarctation of the aorta. It occurs when the aorta, the body's largest artery, is narrower than usual from birth. Consequently, the heart must exert greater force to pump blood throughout the body, resulting in high blood pressure.⁵

Other potential causes 

• Drug-induced hypertension: Caused by various medications, including non-steroidal anti-inflammatory drugs (NSAIDs), antidepressants, atypical antipsychotics such as clozapine and olanzapine, oral contraceptives, sodium-containing antacids, decongestants like phenylephrine or pseudoephedrine, and many others
• Obstructive sleep apnea: This interruption can result from relaxation of the throat walls or blockage by excess tissue. When this occurs, the body responds by releasing chemicals that increase blood pressure
• Pre-eclampsia: When there is a problem with the placenta during pregnancy, a condition called pre-eclampsia might occur, causing blood pressure to increase and resulting in the presence of proteins in urine along with other symptoms⁷ 

What are the symptoms?

The symptoms of secondary hypertension may vary depending on the underlying cause. However, a common feature shared across different causes is the difficulty in managing blood pressure using typical medications that are usually effective for primary hypertension. The patient may be resistant to medication and not respond to standard treatments. If the underlying cause of elevated blood pressure is not addressed first, the chances of treating high blood pressure will be very low.⁵

Diagnosing secondary hypertension

While most people who seek treatments for hypertension typically have primary hypertension, it is important to always watch for the signs of underlying conditions that may be causing hypertension. Some indicators of secondary hypertension include:¹⁰

• Non-responsiveness to standard medications
• Manifestation of signs or symptoms suggestive of other conditions, such as high levels of sweating, increased heart rate, weight gain or loss, abnormal hair growth, irregular menstrual cycles, heat or cold intolerance, weakness, sleep disturbances, excessive fatigue, and more
• The onset of hypertension at a younger age (30 years and below) without traditional risk factors or family history
• Abnormal findings in laboratory tests
• Sudden worsening of hypertension in a patient with previously stable control

When healthcare providers observe any of the above indicators, further evaluation will be conducted to establish a diagnosis. In addition to history-taking and physical examination, additional tests may include:⁷

• Kidney function tests (creatinine, urea, glomerular filtration rate), and detection of protein in the urine
• Electrolyte levels in the body, especially calcium and potassium
• Hormonal function tests, such as plasma aldosterone/renin ratio and thyroid function tests (TSH, T4/T3 levels)
• Imaging modalities like ultrasound, Magnetic Resonance Imaging (MRI), Computerised Tomography (CT) scans, and biopsies for patients suspected of having tumours or malignancies
• Renal Doppler ultrasound to diagnose renal artery stenosis
• Dexamethasone suppression test for suspected Cushing’s syndrome
• Any other additional tests suitable for diagnosing or excluding certain conditions

Treatment approaches

As secondary hypertension has identifiable causes, addressing those causes is crucial to achieving treatment goals. Treating the underlying cause can lead to improvement in hypertension and can provide a potential cure rather than temporary symptom management. Management of this condition typically involves a multidisciplinary approach involving various specialities. In general, the treatment approach will include:

Anti-hypertensive medications

• Diuretics: Help the body eliminate sodium and water
• ACE inhibitor: Helps reduce blood pressure by blocking the angiotensin-converting enzyme (ACE) that narrows blood vessels
• Beta-blockers: This medication will slow the heartbeat and reduce heart workload
• Calcium channel blocker: Relaxes blood vessels and slows the heart rate

Lifestyle modifications

• Dietary changes, mainly controlling salt intake
• Weight management if you are overweight or obese
• Exercising regularly
• Avoid smoking and limit alcohol consumption

Other approaches based on underlying causes, such as:

• Surgical or medical treatment for hormonal imbalance
• Medications, angioplasty, or surgery for kidney disease
• Continuous positive airway pressure (CPAP) for sleep apnea
• Revascularisation for fibromuscular dysplasia

FAQs

What is the most common cause of secondary hypertension?

The most common underlying causes of secondary hypertension are:⁵

• Renal parenchymal disease
• Endocrine disorder
• Renovascular disorder

What is the difference between secondary hypertension with essential/primary hypertension?

The main difference is that in primary hypertension, there is no specific or definitive cause, while in secondary hypertension, the cause is known. Most people with hypertension have primary hypertension. The attributed risk factors for primary hypertension are family history, age, and lifestyle habits.¹¹

Can secondary hypertension be cured?

Yes, once the main cause of it is treated. However, it is important to note that many factors can potentially affect the treatment outcomes. 

What kind of foods can cause high blood pressure?

Foods that are high in salt (sodium) and sugars will contribute to high blood pressure.¹²

Which type of hypertension is life-threatening?

The most critical form of hypertension is known as a hypertensive emergency. It occurs when your blood pressure rises above 180/120 mmHg and is accompanied by evidence of organ damage, such as damage to the heart, eyes, or kidneys. When a person is experiencing this, the treatment has to be immediate to prevent life-threatening complications such as stroke, heart attack, or organ failure.¹³

Summary

Secondary hypertension occurs when high blood pressure is caused by a specific identifiable condition. The main difference between secondary hypertension and primary hypertension lies in its cause. Some of the most prevalent causes of secondary hypertension include:

• Renovascular disease
• Renal diseases such as chronic kidney disease, polycystic kidney disease, glomerulonephritis, chronic pyelonephritis, and congenital abnormalities
• Endocrine problems, including Cushing syndrome, primary aldosteronism, and adrenal gland tumours
• Other causes such as coarctation of the aorta, pregnancy, medications, and sleep apnea

When there are indications that your hypertension may not be primary, healthcare providers will conduct additional evaluations to diagnose the underlying condition. Treating the underlying cause can improve hypertension and provide a potential cure for the cause rather than just giving temporary symptom relief.