A Legion of Inflammation: Legionella-Induced Nephritis

Introduction: Acute interstitial nephritis (AIN) is an acute inflammatory process of the renal interstitium with varied clinical manifestations and drugs being the most common offendor. Infections or autoimmune disease can incite or potentiate AIN. We present a case of pulmonary renal syndrome initially thought to be vasculitis that ultimately proved to be infection related AIN. Case Description: A 60-year-old female presented with 2 days of fever and dyspnea. Physical examination showed diffuse crackles bilaterally. Sodium was 132mEq/L, total CO2 14mmol/L, anion gap 17mmol/L, creatinine 6.36mg/dL (baseline 0.97mg/dL), CK 4282, AST 230, ALT 80, alk phos 128, and bilirubin 0.4. Urinalysis showed 1+ proteinuria, 2+ blood, 25-50 white cells/hpf, and >100 rbc/hpf without dysmorphic features or rbc casts. CT chest showed multifocal pneumonia, and treated with ceftriaxone and azithromycin. Pulmonary and kidney function declined requiring mechanical ventilation and dialysis. No active bleeding seen on bronchoscopy. ANCA and anti-GBM antibodies were negative. Legionella PCR from a tracheal aspirate returned positive. Kidney biopsy showed interstitial infiltration by mononuclear leukocytes with a few admixed neutrophils and eosinophils consistent with AIN. There was marked interstitial edema and peritubular capillaritis. A few granular casts stained positive for myoglobin. After treatment and control of infection, she was treated with a tapering course of prednisone over 3 weeks and had recovery of kidney function within 3 months. Discussion: The patient’s AKI was most likely due to Legionella-related severe AIN with mild pigment nephropathy, both of which may complicate Legionella infection. Legionella is an uncommon cause of pulmonary renal syndrome. Given overlapping clinical features, it is important to consider toxic, infectious and autoimmune causes of AKI. Kidney biopsy is warranted when the diagnosis remains uncertain to help define prognosis and management. Corticosteroids may have a role for persistent kidney dysfunction after treatment of infection.