Acute interstitial nephritis

Question 1

What is the primary cause of acute interstitial nephritis (AIN)?

Answer 1

AIN is caused by hypersensitivity reactions to medications (most common), infections, or systemic diseases, leading to interstitial inflammation and renal dysfunction.

Question 2

Which medications are most commonly associated with acute interstitial nephritis (AIN)?

Answer 2

• Antibiotics (beta-lactams like penicillins, cephalosporins, sulfonamides, rifampin)
• NSAIDs
• Proton pump inhibitors (PPIs, e.g., omeprazole)
• Diuretics (loop diuretics, thiazides)
• Antivirals (acyclovir), anticonvulsants (phenytoin), allopurinol

Question 3

What autoimmune disorders cause acute interstitial nephritis (AIN)?

Answer 3

• Sarcoidosis
• Sjögren syndrome
• Systemic lupus erythematosus (SLE)

Question 4

What are some infectious causes of acute interstitial nephritis (AIN)?

Answer 4

• Legionella, Mycobacterium tuberculosis, Cytomegalovirus (CMV), Epstein-Barr virus (EBV)

Question 5

What are the classic clinical features of acute interstitial nephritis (AIN)?

Answer 5

• Acute kidney injury (rising creatinine, oliguria or normal urine output)
• Fever, rash, arthralgias (though rarely all present together)
• Malaise, nausea, non-bloody vomiting

Question 6

What are the characteristic urinalysis findings in acute interstitial nephritis (AIN)?

Answer 6

• WBC casts (suggesting tubulointerstitial inflammation)
• Pyuria (white blood cells in urine) without infection
• Mild proteinuria
• Eosinophiluria (detected by Wright or Hansel stain, though nonspecific)

Question 7

What is the most specific histopathologic finding of acute interstitial nephritis (AIN) on renal biopsy?

Answer 7

Tubulointerstitial mononuclear cell infiltration (T cells, macrophages) with edema, often with eosinophils.

Question 8

How can AIN be differentiated from acute tubular necrosis (ATN)?

Answer 8

• AIN has WBC casts, ATN does not.
• AIN has eosinophilia/eosinophiluria, ATN does not.
• AIN is often medication-induced, ATN is usually due to ischemia (shock, sepsis) or nephrotoxins (aminoglycosides, contrast).

Question 9

How is acute interstitial nephritis (AIN) diagnosed?

Answer 9

AIN is diagnosed clinically based on medication exposure, eosinophilia, and urine findings. Biopsy is rarely needed.

Question 10

What is the first-line treatment for acute interstitial nephritis (AIN)?

Answer 10

• Discontinue the offending drug immediately.
• If renal function does not improve within a few days, corticosteroids may be considered.
• Supportive care (hydration, electrolyte management).

Question 11

What is the prognosis of acute interstitial nephritis (AIN)?

Answer 11

• Most cases resolve after stopping the offending agent, but some progress to chronic kidney disease (CKD).
• Early steroid use may help in severe cases.