Renal Artery Stenosis

Snapshot

• A 23-year-old woman with no significant past medical history presents to her primary care physician for an annual physical exam.  She was found to have a blood pressure of 156/94 mmHg. She has never had any episodes of high blood pressure in the past and she has no family history of hypertension. She is prescribed captopril. After two weeks, she presents to the emergency room with hypertensive urgency. Captopril was immediately stopped and after stabilizing her blood pressure, an ultrasound revealed bilateral renal artery stenosis.

Introduction

• Clinical definition
  • renal artery stenosis (RAS) occurs when one or both of the renal arteries are narrowed
    • this often causes renovascular hypertension
• Epidemiology
  • prevalence
    • 7% in the United States
    • present in up to 1/3 of patients with malignant or resistant hypertension
  • demographics
    • atherosclerotic disease
      • patients > 50 years of age
    • fibromuscular dysplasia
      • young women
  • risk factors
    • atherosclerosis and its risk factors (e.g., smoking and fatty diet)
    • fibromuscular dysplasia
    • in kidney transplant patients
    • high calcium or phosphorous levels
    • high low-density lipoprotein cholesterol levels
• Pathogenesis
  • narrowing of artery lumen due to
    • atherosclerosis
    • fibromuscular dysplasia
    • narrowed arteries lead to reduced renal perfusion
      • reduced perfusion leads to activation of renin-angiotensin system 
        • increased renin → hypertension, hypokalemia, and hypernatremia
      • chronic renal hypoperfusion leads to chronic stimulation and hyperplasia of the juxtaglomerular apparatus 
      • unilateral renal stenosis 
        • angiotensin II induces pressure natriuresis of the non-stenotic kidney causing hyponatremia in conjunction with hypertension 
      • bilateral renal stenosis 
        • can lead to volume overload
        • heart failure
        • pulmonary edema
• Associated conditions
  • other manifestations of atherosclerotic disease
    • carotid artery disease
    • lower extremity artery disease
    • coronary heart disease
• Prognosis
  • prognostic variable
    • negative
      • elevated serum creatinine
      • comorbid heart disease
      • comorbid chronic obstructive pulmonary disease (COPD)
  • survival with treatment
    • 91% at 1 year
    • 67% at 5 years
• 41% at 10 years

Presentation

• History
  • hypertension before 30 years of age
    • if abrupt onset in a young women, consider fibromuscular dysplasia
  • resistant or malignant hypertension
  • worsening renal function after taking an ACE inhibitor or angiotensin receptor blocking (ARB) agent
    • may indicate bilateral renal artery stenosis (RAS) because ACE inhibitors and ARBs further decrease glomerular filtration rate and worsen renal function
  • sudden unexplained volume overload (heart failure or pulmonary edema)
• Physical exam
  • extremities
    • may have edema if volume overloaded
  • abdomen
    • abdominal or flank bruit through systole and diastole
  • vitals
• hypertension

Imaging

• Ultrasound
  • indications
    • often initial imaging in those < 60 years of age in patients with suspected RAS
  • sensitivity and specificity
    • sensitivity 88-93%
    • specificity 82-89%
• CT angiography
  • indications
    • in patients with normal renal function and suspected RAS
  • sensitivity and specificity
    • sensitivity 90%
    • specificity 94%
• MR angiography
  • indications
    • in patients with renal insufficiency and suspected RAS
  • sensitivity and specificity
    • sensitivity 75-97%
• specificity 64-93%

Studies

• Labs
  • serum creatinine to assess renal function
    • elevated creatinine may indicate atherosclerosis-associated RAS
    • normal creatinine may indicate fibromuscular dysplasia-associated RAS
  • urine protein to assess renal function
    • typically below nephrotic range (< 3.5 g in 24 hours)
• Invasive catheter angiography
  • gold standard for diagnosis
  • only indicated if high suspicion of disease but inconclusive imaging or if revascularization is planned
• Histology
  • fibromuscular dysplasia
    • medial fibroplasia
• Diagnostic criteria  
  • reduction of diameter of > 60%
• string-of-beads appearance on angiography in fibromuscular dysplasia

Differential

• Essential hypertension
  • typically responsive to therapy
• Primary hyperaldosteronism
  • high levels of aldosterone
• Obstructive sleep apnea
• lethargy and fatigue

Treatment

• Medical
  • ACE-inhibitors or ARBs 
    • indications
      • persistent hypertension
    • contraindicated in bilateral RAS or RAS in patients with single kidney  
  • calcium channel blockers or β-blockers
    • given if patients do not respond to ACE-inhibitors or ARBs
• Operative
  • revascularization
    • indications
      • severe complications of RAS
        • unexplained heart failure
        • unexplained pulmonary edema
        • chronic kidney disease
        • inadequately controlled hypertension
    • outcomes
      • may not improve outcomes in those with atherosclerotic RAS
      • cures up to 58% of hypertension in patients with fibromuscular dysplasia-associated RAS
    • complications
      • contrast-induced acute kidney injury or allergic reaction (< 3%)
• bleeding, hematoma, or arteriovenous fistula

Complications

• Renal dysfunction can progress to end-stage renal disease
  • incidence
    • 4% in one study of 68 adults over 39 months
  • treatment
    • dialysis and kidney transplant