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Acute Interstitial Nephritis

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Overview

Acute interstitial nephritis (AIN) describes inflammation of the kidney interstitium usually triggered by a hypersensitivity reaction to drugs. It classically presents with a triad of rash, fever, and eosinophilia, however, this occurs rarely.

Causes

Drugs

Drugs are the most common cause of AIN and include:

  • Nearly all penicillins and cephalosporins
  • NSAIDs
  • Rifampicin
  • Proton pump inhibitors
  • Allopurinol

Other causes

Other causes include:

Presentation

Patients classically have a reduction in kidney function without oliguria within days of starting a causative drug. Other features include:

  • The classic triad of AIN – rarely appears as all three (<10% of cases):
    • Rash
    • Fever
    • Eosinophilia
  •  Elevated serum immunoglobulin E (IgE)

Differential Diagnoses

Acute tubular necrosis (ATN)

  • Eosinophilia, rash, and elevated IgE make ATN less likely
  • Urinalysis may show muddy brown casts in ATN

Investigations

  • Urea and electrolytes (U&Es):
    • Urea and creatinine are elevated
  • Urinalysis:
    • May show sterile pyuria – white cells in the urine with a negative bacterial culture
    • Mild-moderate proteinuria may be seen
  • Full blood count (FBC) and white cell differential:
    • May show eosinophilia
  • Trial of discontinuing suspected causative medication:
  • Kidney biopsy – only test that gives a definitive diagnosis:
    • Generally performed if AKI does not improve when withdrawing a causative medication, where the diagnosis is unclear, or if treatment involving immunosuppressants (e.g. corticosteroids) is being considered
    • May show inflammatory infiltrates in the interstitium with varying numbers of eosinophils, lymphocytes and plasma cells

Management

Management involves:

  • Withdrawal of the offending drug
  • Supportive care (e.g. correcting derangements in U&Es and fluid balance)
  • Corticosteroids may be considered in some cases

Complications

The main complication is the development of chronic kidney disease (CKD).

Prognosis

  • Most patients with drug-induced AIN have some degree of impaired kidney function
  • The prognosis is worse with delayed diagnosis and/or management

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