II. Pathophysiology

  1. Renal interstitial inflammation
  2. T-Cell mediated Hypersensitivity Reaction (Allergic Reaction affecting the Kidney)

III. Causes

  1. See Infectious Causes of Acute Interstitial Nephritis (includes miscellaneous causes)
  2. Medications
    1. See Medication Causes of Interstitial Nephritis
    2. Most common causes
      1. NSAIDs
      2. Antibiotics
      3. Proton Pump Inhibitors

IV. Findings: Symptoms and Signs

  1. Classic Presentation of rash, fever and urine Eosinophilia in only 10% of patients (within days of starting causative medication)
  2. Classic Symptom Triad (e.g. Methicillin induced Hypersensitivity)
    1. Low grade fever (>70% of cases)
    2. Rash (>30% of cases)
    3. Arthralgia (>15% of cases)
  3. Acute Renal Failure
    1. Oliguria
    2. Malaise
    3. Nausea or Vomiting

V. Labs: General

  1. Urinalysis
    1. Eosinophiluria
    2. Proteinuria
    3. Fractional Excretion of Sodium >1%
      1. Common to intrinsic Kidney disease (ATN, GN) in which Sodium cannot be retained despite decreased perfusion
  2. Renal Function tests with Renal Insufficiency
    1. Serum Creatinine increased
    2. Blood Urea Nitrogen increased
  3. Miscellaneous
    1. Hyperchloremic Metabolic Acidosis

VI. Labs: Renal biopsy

  1. Inflammation of renal interstitium
    1. Mononuclear cell and T-Lymphocyte infiltrate
  2. Glomerular and vascular sparing

VII. Management

  1. Consider Corticosteroid course
    1. Initial: Prednisone 1 mg/kg/day PO for 2 weeks
    2. Next: Prednisone tapered off over 3-4 weeks
    3. Consider Cyclophosphamide in steroid non-responders
  2. Eliminate possible causes
  3. Optimize fluid status
  4. Manage Hyperkalemia and other Electrolyte abnormalities
  5. Symptomatic relief of fever and Arthralgias
  6. Avoid nephrotoxic medications

VIII. Prognosis

  1. Recovery in weeks if cause eliminated within 2 weeks
  2. Renal biopsy findings suggestive of poor prognosis
    1. Diffuse inflammation
    2. Neutrophils >1%
    3. Significant interstitial fibrosis

IX. Complications

  1. Acute Renal Failure
    1. Responsible for up to 15% of Acute Renal Failure

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