Chronic tubulointerstitial nephritis (CTIN) is a condition of chronic inflammation of the renal tubules and interstitium and can progress to end-stage renal disease (ESRD) after months or years.

Pathophysiology

• Analgesic nephropathy (e.g., resulting from NSAIDs use)
  • Inhibition of prostacyclin synthesis → vasoconstriction of the medullary blood vessels → papillary ischemia and papillary necrosis
  • Associated with an increased risk of urothelial carcinoma; can progress to ESRD

Etiology

• Medications
  • Analgesic nephropathy: combination analgesics , NSAIDs, and acetaminophen

Clinical features

• Painless hematuria, pyuria, oliguria, or polyuria
• Colicky flank pain

Diagnostics

• Blood tests: ↑ BUN and creatinine, ↓ K⁺ or ↑ K⁺; normal anion gap ; anemia of CKD
• Urine chemistries in tubulointerstitial diseases (findings similar to ATIN): sterile pyuria, proteinuria, hematuria, RBC casts, WBC casts
• Renal biopsy: tubulointerstitial fibrosis and tubular atrophy