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Interstitial nephritis
Interstitial nephritis

Interstitial nephritis

Acute interstitial nephritis (AIN) refers to the inflammation of the interstitial space between the tubules within the kidney. This is distinct from glomerulonephritis which involves inflammation of the glomerulus and around it.

There is chronic interstitial nephritis (CIN) and we will touch on this briefly at the end.

Pathophysiology

AIN is believed to be a type I or type IV hypersensitivity reaction leading to infiltration of immune cells.

It commonly occurs due to drugs or infection:

⚠️
Drugs that may cause AIN:
  • NSAIDs
  • Beta-lactam antibiotics such as carbapenems, monobactams, cephalosporins, penicillins.
  • PPIs
  • Immunotherapy cancer drugs
    • PD-1 inhibitors - nivolumab
    • PD-L1 inhibitors - atezolizumab, avelumab, durvalumab
    • CTLA-4 inhibitors - ipilimumab
  • Diuretics
  • H2 antagonists such as cimetidine and rantidine

Other drugs include: allopurinol, phenytoin, mesalazine, warfarin.

Infectious causes may be viral, parasitic, fungal and bacterial (commonly rickettsia and mycobacteria)

⚠️ Risk factors

  • Use of AIN causing drugs
  • HIV - through multiple mechanisms, including antiretroviral drug usage that can cause damage as well as increased risk of infections that may cause AIN.
  • Inflammatory diseases - such as sarcoidosis, Sjögren’s syndrome or SLE.
  • Uveitis - this is known as tubulo-interstitial nephritis with uveitis (TINU) which mainly occurs in young females.

😷 Presentation

It’s presentation is vague and so a good history is important, especially when using offensive drugs.

  • AKI
  • Fever
  • Rash
  • Arthralgia
  • Uveitis
🔺
Hypersensitivity triad:
  1. Fever
  2. Rash
  3. Eosinophilia

However, this is only seen in <10% of patients actually.

🔍 Investigations

  1. 🥇 Serum urea and creatinine - raised (indicative of AKI).
  2. 🥇 Urinalysis - sterile pyuria & white cell casts along with low-grade proteinuria.
  3. 🥇 FBC - eosinophilia.
  4. 🏆 Kidney biopsy - gold-standard and the only test that can confirm diagnosis. It will show interstitial immune infiltrates.

🧰 Management

☠️
Drug-related AIN:
  1. Discontinuation of offensive drug
  2. Supportive care - monitoring electrolytes, urea and creatinine.
🔥
Inflammatory disease-related AIN:

Oral corticosteroids are first-line.

If these are not effective, we can consider diuretics and dialysis.