What are the causes of hypertension?

Causes of Hypertension

Hypertension can be classified as primary (essential) hypertension, accounting for 90-95% of cases with no identifiable cause, or secondary hypertension, which has specific underlying causes that may be potentially reversible. 1

Primary Hypertension

Risk Factors and Contributing Elements

• Lifestyle factors:

  • Weight gain/obesity
  • High-sodium diet
  • Decreased physical activity
  • Excessive alcohol consumption (>3 drinks/day) 2
  • Job changes requiring increased travel and meals away from home 2

• Non-modifiable factors:

  • Family history of hypertension
  • Advancing age
  • Male sex (higher risk than females) 2
  • Genetic predisposition 2

Secondary Hypertension (5-10% of cases)

Common Causes

1. Obstructive Sleep Apnea:

   • Most prevalent secondary cause, especially in resistant hypertension
   • Present in up to 83% of patients with resistant hypertension
   • Mechanism: Intermittent hypoxemia leads to increased sympathetic nervous system activity 2

2. Renal Parenchymal Disease:

   • Presents with edema, fatigue, frequent urination
   • Detected through abnormal eGFR, urinalysis, renal ultrasound 2

3. Primary Aldosteronism:

   • Present in approximately 20% of resistant hypertension cases
   • Often without hypokalemia in early stages
   • Screening: Aldosterone-to-renin ratio 2, 3

4. Renovascular Hypertension:

   • Due to renal artery stenosis (atherosclerotic or fibromuscular dysplasia)
   • More common in older patients (atherosclerotic) or young women (fibromuscular dysplasia)
   • Screening: Renal Doppler ultrasound, CT/MR angiography 3

Less Common Causes

1. Pheochromocytoma:

   • Presents with episodic hypertension, headaches, palpitations, sweating
   • Screening: 24-hour urinary or plasma metanephrines 2, 3

2. Cushing's Syndrome:

   • Features: Central obesity, facial rounding, easy bruising
   • Screening: 24-hour urinary free cortisol, dexamethasone suppression test 2, 3

3. Thyroid Disorders:

   • Hyperthyroidism: Increased cardiac output
   • Hypothyroidism: Increased peripheral resistance
   • Screening: Thyroid-stimulating hormone 3

4. Hyperparathyroidism:

   • Associated with hypercalcemia
   • Screening: PTH, calcium, phosphate levels 3

5. Aortic Coarctation:

   • More common in children and young adults
   • Physical finding: BP difference between arms and legs
   • Diagnosis: Echocardiogram, CT angiogram 3

Drug-Induced Hypertension

• Medications that can cause or worsen hypertension:
  • NSAIDs
  • Oral contraceptives
  • Corticosteroids
  • Decongestants
  • Anticancer drugs (especially vascular endothelial growth factor inhibitors)
  • Recreational drugs (cocaine, amphetamines) 2

Clinical Features Suggesting Secondary Hypertension

History and Physical Examination

• Onset of hypertension before age 30 or after age 50 1
• Severe or resistant hypertension (BP >140/90 mmHg despite three medications including a diuretic) 3
• Sudden worsening of previously controlled hypertension
• Specific symptoms:
  • Snoring, hypersomnolence (sleep apnea)
  • Muscle cramps, weakness (hypokalemia from aldosteronism)
  • Episodic headaches, palpitations, sweating (pheochromocytoma)
  • Weight loss, heat intolerance (hyperthyroidism) 2

Physical Examination Findings

• BP differences between arms or between arms and legs
• Abdominal or carotid bruits (renovascular disease)
• Cushingoid features (central obesity, facial rounding, striae)
• Enlarged kidneys (polycystic kidney disease)
• Neck circumference >40 cm (sleep apnea) 2

Laboratory and Diagnostic Testing

• Basic testing for all hypertensive patients:

  • Fasting blood glucose
  • Complete blood count
  • Lipid profile
  • Serum creatinine with eGFR
  • Serum electrolytes (sodium, potassium, calcium)
  • Thyroid-stimulating hormone
  • Urinalysis
  • Electrocardiogram 2

• Additional testing when secondary causes are suspected:

  • Specific hormone tests
  • Imaging studies
  • Sleep studies 3

Clinical Approach

When evaluating a patient with hypertension, consider the possibility of secondary causes, particularly in patients with:

• Resistant hypertension
• Young age of onset
• Severe hypertension with target organ damage
• Specific symptoms or physical findings suggestive of secondary causes
• Abnormal basic laboratory tests 1, 4

Early identification of secondary causes is crucial as some forms may be potentially curable or require specific treatment approaches beyond standard antihypertensive therapy.