Can interstitial nephritis present similarly to the described vignette?

Can Interstitial Nephritis Present Like the Above Vignette?

Yes, interstitial nephritis can absolutely present with the clinical features described in the vignette, and should be high on your differential diagnosis for acute kidney injury with these findings. 1, 2

Clinical Presentation of Acute Interstitial Nephritis

Acute interstitial nephritis (AIN) is notably pauci-symptomatic and non-specific in its presentation, which makes it a diagnostic chameleon that can mimic many other renal conditions 3. The classic triad of fever, rash, and arthralgias is absent in up to two-thirds of patients, so don't rely on these features to make or exclude the diagnosis 4.

Common Presenting Features

AIN typically presents with:

• Acute kidney injury with slowly rising serum creatinine - often the only finding 1, 3
• Oliguria - present in some cases 1, 5
• Hematuria and sterile pyuria - frequently seen on urinalysis 4, 3
• White blood cell casts - highly suggestive of interstitial inflammation 6
• Peripheral edema - can occur 1
• Anorexia and nonspecific constitutional symptoms 1

Proteinuria in Interstitial Nephritis

A critical pitfall: interstitial nephritis can present with moderate-to-heavy proteinuria (>1 g/day), even nephrotic-range proteinuria, contrary to traditional teaching 5. This occurs due to cytokine-like permeability factors secreted by inflammatory cells in the interstitium, and does not require concurrent glomerulonephritis 5. This presentation is uncommon but well-documented, so don't exclude AIN just because proteinuria is substantial.

Etiologic Considerations

Medications cause 80-90% of AIN cases 1. The most common culprits include:

• Antibiotics (especially beta-lactams, but many others) 1, 7
• NSAIDs 2, 7
• Proton pump inhibitors 2
• Immune checkpoint inhibitors (presenting 3-10 months after initiation) 1, 2
• Diuretics 7

Less commonly, AIN can result from infections (including acute pyelonephritis with subsequent chronic granulomatous interstitial nephritis) 8, systemic diseases like inflammatory bowel disease 9, or be idiopathic 5.

Diagnostic Approach

The key diagnostic steps are:

1. Review all medications - look for recent additions or changes in the past 3-10 months 1
2. Urinalysis with microscopy - specifically look for WBC casts, eosinophiluria, sterile pyuria, and hematuria 6, 4, 3
3. Rule out other causes - exclude hypovolemia, obstruction, IV contrast exposure, and other nephrotoxic insults 2
4. Check for systemic features - eosinophilia, fever, rash (though often absent) 4, 3

Renal biopsy remains the gold standard for definitive diagnosis, showing normal glomeruli with patchy interstitial infiltrate containing lymphocytes, plasma cells, and eosinophils 7, 4. However, biopsy may not be required in mild cases with rapid improvement after removing the offending agent 4. Consider biopsy if renal function doesn't improve within 5-7 days of withdrawing the suspected causative medication 3.

Important Caveats

• Granulomatous interstitial nephritis can occur and may be associated with small vessel vasculitis 5
• Confusion or altered mental status in the setting of AIN suggests severe uremia or electrolyte disturbances requiring urgent intervention 2
• Normal complement levels and negative autoantibodies are typical, helping distinguish AIN from glomerulonephritis 5
• Imaging is typically unrevealing - kidneys may appear normal or show increased echogenicity in 30-40% of cases 1

The time from exposure to removal of the offending agent is the most important prognostic factor for recovery of renal function 4. Early recognition and immediate discontinuation of the causative medication is paramount 2.