Acute Interstitial Nephritis

Snapshot

• A 60-year-old man presents to the emergency room with a 1-day history of fever and a new skin rash. He is taking methicillin for a soft tissue infection. On physical exam, he has costovetebral tenderness, and a diffuse maculopapular rash over his trunk. His serum creatinine is elevated at 3 mg/dL. Urinalysis reveals white blood cells. Further testing with Wright stain is positive for eosinophils in the urine.

Introduction

• Clinical definition
  • acute interstitial nephritis (AIN), also known as tubulointerstitial nephritis, is an acute immune-mediated interstitial inflammation of the kidneys
• Epidemiology
  • demographics
    • middle-aged adults
• Etiology
  • drug-induced hypersensitivity (majority of cases)  
    • typically developed between 1 week to 9 months
    • 5 Ps
      • Pee (diuretics, especially sulfa ones)
      • Pain-free (NSAIDs)
      • Penicillins and cephalosporins
      • Proton pump inhibitors
      • rifamPin
  • systemic infections
  • autoimmune diseases
    • systemic lupus erythematosus
    • sarcoidosis
• Pathogenesis
  • type IV hypersensitivity reaction
  • T-cell-mediated attack on tubular cells
• Prognosis
• typically resolves after withdrawal of inciting agent

Presentation

• Symptoms
  • primary symptoms
    • fever
    • hematuria
    • arthralgia
    • can be asymptomatic
• Physical exam
  • rash
    • maculopapular
• flank/costovertebral angle tenderness

Studies

• Labs 
  • serum eosinophilia
  • elevated serum creatinine
• Urinalysis with microscopy and sediment analysis
  • white blood cell casts 
  • hematuria
  • eosinophiluria
    • seen with Hansel or Wright stain
• Renal biopsy
  • not usually indicated
• Histology
  • severe tubular damage
  • interstitial edema
  • T-cell and eosinophilic infiltration
• Diagnostic criteria
  • elevated creatinine
• urinalysis with white cell casts and eosinophiluria

Differential

• Acute tubular necrosis from NSAIDs
  • no rash or eosinophils
• Renal atheroemboli
  • also presents with eosinophiluria, eosinophilia, and skin rash
• rash is typically livedo reticularis with digital infarcts and not maculopapular

Treatment

• Conservative
  • discontinue inciting drug 
    • indications
      • for all drug-induced hypersensitivity cases
• Medical
  • glucocorticoids      
    • indications
• if creatinine continues to rise after stopping drugs

Complications

• Renal failure requiring dialysis