Makindo Medical Notes

Related Subjects: |Metabolic acidosis |Lactic acidosis |Acute Kidney Injury (AKI) / Acute Renal Failure |Renal/Kidney Physiology |Chronic Kidney Disease (CKD) |Anaemia in Chronic Kidney Disease |Analgesic Nephropathy |Medullary Sponge kidney |IgA Nephropathy (Berger's disease) |HIV associated nephropathy (HIVAN) |Balkan endemic nephropathy (BEN) |Autosomal Dominant Polycystic kidney disease

The classic triad of fever 🌡️, rash 🤒, and eosinophilia 🧪 suggests a systemic hypersensitivity reaction. A renal biopsy should be considered in any patient with non-oliguric acute renal failure (ARF) to confirm the diagnosis of AIN.

About 📖

• Acute Interstitial Nephritis (AIN): An immune-mediated inflammation of the renal interstitium and tubules.
• Always consider new drug exposures 💊 – antibiotics are the most common offenders.
• Unlike many other AKI causes, patients are often non-oliguric (still passing urine) 🚰.

Aetiology 🧬

• Immune-mediated inflammation: Often triggered by drugs, but also autoimmune or infectious causes.
• Histology shows lymphocytes, neutrophils, and eosinophils 🧪 (especially if drug-induced).
• Interstitial oedema and tubulitis contribute to impaired renal function.

Clinical Features 🩺

• Acute renal failure (AKI): Rapid rise in creatinine and urea ⚠️.
• Fever 🌡️ + Rash 🤒 + Eosinophilia 🧪: The “classic triad,” though not always present.
• Flank/lumbar pain: From renal capsule distension.
• May mimic Fanconi syndrome or renal tubular acidosis due to tubular dysfunction.
• Systemic malaise, nausea, and occasionally arthralgia.

Causes 🔍

• Drugs 💊: Proton pump inhibitors, NSAIDs, penicillin, allopurinol, mesalazine (delayed).
• Immune 🧬: Autoimmune disease, transplant rejection.
• Infections 🦠: Pyelonephritis, leptospirosis, TB, hantavirus, legionella.
• Toxins 🧫: Myeloma light chains, mushroom poisoning (Cortinarius).
• Others: Sarcoidosis, systemic diseases.

Investigations 🧪

• U&E: AKI picture – raised creatinine, +/- hyperkalaemia.
• FBC/ESR: Inflammatory response (raised ESR, eosinophilia).
• Urinalysis: Mild proteinuria (<1 g/day), haematuria, pyuria, WCC casts. Hansel stain may show eosinophils (not always present).
• Urine culture: Usually sterile ❌.
• Renal biopsy (gold standard): Interstitial infiltrate (lymphocytes, plasma cells, eosinophils). Granulomas may be seen in sarcoid or drug-induced AIN.

Management ⚕️

• Withdraw offending agent 💊: Most cases recover once the trigger is removed.
• Treat underlying cause: e.g., infection or autoimmune disease.
• Corticosteroids: Early high-dose steroids (e.g., prednisolone 1 mg/kg/day for ≥2 weeks) can accelerate renal recovery if biopsy-proven AIN.
• Supportive care: Correct fluid/electrolyte imbalance, monitor renal function.

Key Clinical Pearls ✨

• Think of AIN in AKI + rash + new drug exposure 💊.
• Eosinophilia is suggestive but not diagnostic 🧪.
• Renal biopsy is often required for confirmation 🔬.
• Withdrawal of the drug can reverse damage, but delayed recognition risks progression to CKD ⚠️.