What is the difference between primary (essential) hypertension and secondary hypertension?

Distinguishing Primary from Secondary Hypertension

Primary (essential) hypertension accounts for approximately 90% of all hypertension cases and has no identifiable cause, resulting from complex interactions between genetic predisposition and environmental factors, while secondary hypertension represents about 10% of cases and has a specific, potentially reversible underlying cause. 1, 2

Primary Hypertension Characteristics

Pathophysiology:

• Results from multifactorial mechanisms including endothelial dysfunction, increased peripheral vascular resistance, vascular remodeling, dysregulation of the renin-angiotensin-aldosterone system, and abnormal renal sodium handling 2
• Represents a polygenic disorder with no single identifiable cause, involving complex gene-environment interactions 1, 3
• Develops gradually over years, typically associated with modifiable risk factors 2

Key Clinical Features:

• Family history of hypertension is commonly present 1, 4
• Gradual onset with blood pressure increasing over time, often correlating with weight gain and aging 4
• Strong association with obesity (responsible for 40-78% of primary hypertension cases), physical inactivity, high sodium intake, and excessive alcohol consumption 2
• Age-related presentation: in adolescents and adults, 85-95% of hypertension cases are primary 1

Secondary Hypertension Characteristics

Defining Features:

• Accounts for approximately 10% of hypertension in the general population, but increases to 10-35% in resistant hypertension populations 1, 2, 5
• Has a specific, identifiable, and potentially reversible underlying cause 1, 5
• In younger children (school-aged), secondary causes account for 70-85% of cases, with this proportion decreasing with age 1

Clinical Red Flags Suggesting Secondary Hypertension:

• Sudden onset or rapid progression of hypertension 1, 6
• Age of onset younger than 30 years (especially before puberty) 1, 6
• Severe or resistant hypertension (uncontrolled on three or more medications) 1, 5
• Absence of family history of hypertension 7
• Malignant or accelerated hypertension 6
• Acute rise in blood pressure in previously controlled patients 1
• Target organ damage disproportionate to duration or severity of hypertension 1

Physical Examination Findings:

• Features of Cushing syndrome 1
• Skin stigmata of neurofibromatosis (suggesting pheochromocytoma) 1
• Palpable enlarged kidneys (polycystic kidney disease) 1
• Abdominal bruits (renovascular hypertension) 1
• Diminished and delayed femoral pulses with reduced femoral blood pressure (aortic coarctation) 1
• Precordial or chest murmurs 1

Most Common Causes of Secondary Hypertension

In Adults:

• Primary aldosteronism (screen with plasma aldosterone-to-renin ratio in resistant hypertension, spontaneous hypokalemia, adrenal mass, or family history of early-onset hypertension) 1
• Obstructive sleep apnea (present in 83% of treatment-resistant hypertension cases) 7, 8
• Renovascular disease (atherosclerotic renal artery stenosis, especially in older adults) 1, 6
• Chronic kidney disease 8, 6
• Drug-induced hypertension (NSAIDs, oral contraceptives, sympathomimetics, corticosteroids) 1

In Children:

• Renal parenchymal disease 6
• Coarctation of the aorta 6

Diagnostic Approach

When to Screen for Secondary Causes:

• Screen all patients presenting with the clinical red flags listed above 1
• Screen patients with resistant hypertension (uncontrolled on three medications including a diuretic) 1, 5
• More detailed diagnostic work-up is warranted when: the patient is younger, blood pressure is higher, and hypertension developed rapidly 1

Initial Screening Tests:

• Basic metabolic panel (assess renal function and potassium) 4
• Urinalysis 4
• Plasma aldosterone-to-renin ratio (if clinical suspicion for primary aldosteronism) 1
• Sleep apnea screening questionnaire 7
• Thyroid function tests 4
• Renal artery duplex ultrasound (if renovascular disease suspected) 7

Critical Clinical Pitfall

Even when a secondary cause is identified and treated, blood pressure rarely returns to normal with long-term follow-up. 5 This indicates either:

• Concomitant essential hypertension was already present 5
• Irreversible vascular remodeling has occurred from prolonged hypertension exposure 5

Therefore, early detection and treatment of secondary causes are essential to prevent irreversible vascular changes, but most patients will still require ongoing antihypertensive therapy even after addressing the secondary cause 5