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 ⚠️.
