Renal Hypertension: Understanding the Causes

Renal hypertension, also known as secondary hypertension, is a type of high blood pressure caused by underlying kidney disease or abnormalities. This condition can be broadly classified into two main categories — renal parenchymal hypertension and renovascular hypertension. Each has distinct causes and mechanisms that contribute to elevated blood pressure.

Renal Parenchymal Hypertension

Renal parenchymal hypertension is the most common form of secondary hypertension linked to various kidney diseases. Conditions such as acute glomerulonephritis, chronic glomerulonephritis, diabetic nephropathy, chronic pyelonephritis, polycystic kidney disease, and post-kidney transplant complications can all lead to this type of hypertension. In fact, it is estimated that 80–90% of patients with end-stage renal disease also suffer from high blood pressure.

One of the primary reasons for this is the significant loss of functional kidney units, or nephrons. This loss leads to sodium and water retention, which increases extracellular fluid volume. Additionally, activation of the renin-angiotensin-aldosterone system (RAAS) and reduced sodium excretion further elevate blood pressure. As a result, the increased pressure within the glomeruli of the kidneys creates a vicious cycle, worsening kidney damage and further elevating blood pressure.

Renovascular Hypertension

Renovascular hypertension occurs when there is a narrowing or blockage in one or both main renal arteries or their branches. This restriction in blood flow to the kidneys can trigger a hypertensive response due to the activation of the RAAS system as the kidney senses reduced blood flow.

Common Causes of Renal Artery Narrowing

Several conditions can cause renal artery stenosis, including:

• Polyarteritis nodosa — a form of vasculitis commonly seen in younger individuals.
• Fibromuscular dysplasia — a non-inflammatory vascular disorder, often diagnosed in adolescents and young adults.
• Atherosclerosis — the most common cause in older adults, characterized by plaque buildup in the arteries.

If the narrowing is detected and treated early, blood pressure may return to normal following intervention. However, if the stenosis develops over a long period or occurs in individuals who already have essential hypertension, blood pressure may not fully normalize even after the structural issue is corrected.