Emphysematous Pyelonephritis

Emphysematous pyelonephritis is a severe necrotising infection of the renal parenchyma and perirenal tissues caused by gas forming organisms, with gas within the kidney, collecting system or perinephric tissue. Escherichia coli (about 70 percent) and Klebsiella pneumoniae (about 20 percent) are the most common, followed by Proteus, Pseudomonas, Enterobacter and Candida.

Diabetes mellitus is present in 70 to 90 percent (hyperglycaemia and impaired host response). Urinary tract obstruction (stones, papillary necrosis, tumour) is present in about 25 to 40 percent. Women are affected more (about 3 to 6:1), with the left kidney slightly more often.

Mortality is about 20 to 40 percent historically (up to 70 to 80 percent for fulminant disease treated with antibiotics alone). It has fallen to about 10 to 20 percent with modern combined therapy.

Classification by CT:

• class 1: gas confined to the collecting system only (emphysematous pyelitis, mortality 10 percent)
• class 2: gas in the renal parenchyma without extension to the extrarenal space (mortality 10 percent)
• class 3A: extension of gas or abscess to the perinephric space (mortality 29 percent)
• class 3B: extension to the pararenal space (mortality 29 percent)
• class 4: bilateral disease or solitary kidney (mortality 50 percent)

Poor prognostic factors: thrombocytopenia (below 60 x 10^9/L), acute kidney injury (creatinine above 2 to 3 mg/dL), shock, altered mental status, and disseminated intravascular coagulation.

• Fever, chills, flank and abdominal pain, nausea and vomiting, often severe.
• Failure to respond to 48 to 72 hours of antibiotics for presumed pyelonephritis.
• Septic shock, altered mental status, and acute kidney injury.
• Pneumaturia, flank mass and crepitus (rare).
• Hyperglycaemia and diabetic ketoacidosis, metabolic acidosis, and hyperkalaemia.
• Costovertebral angle tenderness; urine shows pyuria, bacteriuria and sometimes frank pus.

• Non-contrast or contrast CT of the abdomen is the diagnostic standard: gas within the renal parenchyma and collecting system (mottled or streaky gas, or crescent of gas), perinephric extension and abscess, and the presence of obstruction, stones or tumour; the CT class guides treatment.
• Plain radiograph (mottled gas over the kidney, crescent sign) and ultrasound (hyperechoic foci with dirty shadowing); CT is far more sensitive.
• Urine and blood cultures (positive in about 50 percent), urine analysis with pyuria and bacteriuria.
• Laboratory: complete blood count (leucocytosis, thrombocytopenia), creatinine, blood glucose, HbA1c, electrolytes, arterial blood gas and lactate, coagulation, and C-reactive protein.
• Assess for obstruction by ultrasound or CT.

Management is aggressive resuscitation and antibiotic therapy, with early drainage or nephrectomy for severe disease, in an intensive care unit setting when septic.

• Resuscitation: intravenous crystalloid (30 mL/kg), vasopressors for shock, control of hyperglycaemia with insulin infusion (target 140 to 180 mg/dL), correction of acidosis and electrolytes, and thromboprophylaxis as appropriate.
• Empiric broad spectrum antibiotics immediately (within 1 hour), adjusted to culture. Options:
  • piperacillin tazobactam 4.5 g every 6 hours
  • meropenem 1 g every 8 hours (for ESBL risk)
  • ceftriaxone 2 g daily plus gentamicin 5 mg/kg daily (adjust to renal function)
  • ciprofloxacin 400 mg every 12 hours
  Duration is 2 to 4 weeks (with an intravenous phase of at least 1 to 2 weeks, followed by oral therapy).
• Relief of obstruction: ureteral stent or percutaneous nephrostomy urgently when obstructed (a critical step, as antibiotic therapy alone fails).
• Class 1 and 2: antibiotics, with percutaneous catheter drainage (pigtail or nephrostomy tube, 8 to 12 Fr) for gas or fluid collections, with success in about 70 to 90 percent; the combination is superior to antibiotics alone.
• Class 3 and 4 or failure to improve in 48 to 72 hours: percutaneous drainage first in a stable patient (renal salvage).
• Emergency nephrectomy for fulminant disease, unresponsive sepsis, diffuse gas with extensive parenchymal destruction, or no response to drainage. Nephrectomy has a mortality of about 10 to 25 percent, and a lower mortality than medical therapy alone for the high risk class.
• Bilateral disease: drainage and antibiotic therapy, with nephrectomy of the worse kidney.
• Management of risk factors: control of diabetes, treatment of stone or obstruction after infection resolves, and avoidance of recurrence.
• Follow up: repeat CT at 1 to 2 weeks, serial creatinine and glucose, ultrasound for residual abscess, and a nuclear renal scan (DMSA) at 3 months to assess residual function.
• Renal replacement therapy may be needed for acute kidney injury; long term chronic kidney disease follows in many.