Secondary Hypertension 

1. When Should You Suspect Secondary Hypertension? 

• Onset <30 years (without obesity/family history)
• Onset >55 years with sudden worsening
• Resistant hypertension (≥3 drugs including diuretic)
• Malignant/accelerated hypertension
• Sudden deterioration in renal function after ACEi/ARB
• Unexplained hypokalaemia
• Episodic headache, palpitations, sweating
• Discrepant arm-leg BP
• Recurrent flash pulmonary oedema

2. Causes of Secondary Hypertension

A. Renal Causes (Most Common)

1️⃣ Renal Parenchymal Disease

Most common cause overall.

Pathophysiology

• ↓ Nephron mass → sodium retention
• RAAS activation
• Volume expansion
• Sympathetic activation

Causes

• Chronic glomerulonephritis
• Diabetic nephropathy
• Reflux nephropathy
• Polycystic kidney disease
• Obstructive uropathy

Clues

• Abnormal urinalysis
• Elevated creatinine
• Small kidneys on ultrasound (except PKD)

Investigation

• Urine protein
• eGFR
• Renal ultrasound

2️⃣ Renovascular Hypertension

Causes

• Atherosclerosis (elderly males)
• Fibromuscular dysplasia (young females)

Pathophysiology

Renal hypoperfusion → RAAS activation → ↑ Angiotensin II → vasoconstriction + aldosterone

Clues

• Resistant HTN
• Flash pulmonary oedema
• Renal bruit
• Rise in creatinine after ACEi

Investigation

• Doppler US
• CT angiography
• MR angiography

Management

• ACEi (caution bilateral)
• Revascularisation (selected cases)

B. Endocrine Causes

1️⃣ Primary Hyperaldosteronism (Conn’s Syndrome)

Pathophysiology

↑ Aldosterone → sodium retention + potassium loss

Clues

• Resistant HTN
• Hypokalaemia
• Metabolic alkalosis

Screening Test

Aldosterone-renin ratio (ARR)

High aldosterone + suppressed renin = diagnostic clue

Confirmatory tests

• Saline suppression test
• Adrenal vein sampling

Management

• Unilateral adenoma → surgery
• Bilateral hyperplasia → spironolactone

Hypertension + hypokalaemia = Think primary aldosteronism

2️⃣ Phaeochromocytoma

Tumour of chromaffin cells.

Classic Triad

• Headache
• Sweating
• Palpitations

Pathophysiology

↑ Catecholamines → α1 vasoconstriction

Diagnosis

• Plasma free metanephrines
• 24-hour urinary metanephrines
• MRI abdomen

Associations

• MEN2
• NF1
• VHL

Management

1. Alpha-blockade (phenoxybenzamine)
2. Then beta-blocker
3. Surgery

Never give beta-blocker before alpha-blockade.

3️⃣ Cushing’s Syndrome

Mechanism

Cortisol has mineralocorticoid activity → sodium retention.

Clues

• Central obesity
• Striae
• Diabetes
• Osteoporosis

Screening

• Overnight dexamethasone suppression test

4️⃣ Thyroid Disorders

Hyperthyroidism

• ↑ Systolic BP
• Wide pulse pressure

Hypothyroidism

• ↑ Diastolic BP

C. Vascular Causes

Coarctation of Aorta

Congenital narrowing of aorta.

Clues

• Young patient
• Radio-femoral delay
• Rib notching
• Upper limb HTN, lower limb hypotension

D. Obstructive Sleep Apnoea (OSA)

Very common cause.

Mechanism

• Intermittent hypoxia
• Sympathetic activation
• RAAS activation

Clues

• Snoring
• Daytime sleepiness
• Resistant HTN

E. Drug-Induced Hypertension

• NSAIDs
• Steroids
• OCP
• Cyclosporine
• Tacrolimus
• Erythropoietin
• Cocaine
• Decongestants

Always take drug history.

3. Investigation Strategy 

Step 1: Basic Screening

• U&E
• Creatinine
• Urine ACR
• TSH
• Fasting glucose
• Lipid profile

Step 2: If Suspicion Based on Clues