Symptoms: Fever, Abdominal Pain, Vomiting
A 55-year-old diabetic woman presents with three days of subjective fevers, generalized abdominal pain, nausea, and vomiting. She is hemodynamically stable, and has a urinalysis significant for 31–75 WBC, 31–75 RBC, and moderate bacteria.
A CT scan of her abdomen and pelvis shows multiple large nonobstructing renal calculi in the right renal pole with intraparenchymal gas.
What is her diagnosis? See p. 24.
Emphysematous pyelonephritis is a life-threatening necrotizing infection of the upper urinary tract characterized by the production of gas within the kidney or perinephric space. The exact incidence of emphysematous pyelonephritis is unknown, with the largest case series to date describing only 522 patients. (Nat Rev Urol 2009;6:272.)
It most commonly affects diabetics (90%), typically women, and immunocompromised patients (Arch Intern Med 2000;160:797), but has been reported to occur in patients with polycystic kidney disease (J Urol 1998;159:1633) and renal transplantation. (Brit J Urol 1995;75:71.) Nondiabetic patients who have a ureteric obstruction are also known to develop emphysematous pyelonephritis 30 percent of the time, so the at-risk population is much larger. (Nat Rev Urol 2009;6:272.)
Emphysematous pyelonephritis is on a spectrum of disease progression that results from gas production in the renal parenchyma. The exact mechanism is unknown, but is thought to require the presence of gas-forming bacteria, impaired tissue perfusion, and elevated glucose levels in the tissues. (Arch Intern Med 2000;160797.) Gas-forming bacterial pathogens that cause it are most commonly E. coli and Proteus, but cases from Klebsiella, anaerobic Streptococcus, Candida, Acinetobacter, Proteus, Streptococcus, Pseudomonas, Bacteroides fragilis, Clostridium, and Aspergillus have been reported. (Urol 2012;79:1281; Nat Rev Urol 2009;6:272.)
Gas localized to the collecting system is known as emphysematous pyelitis, and is considered a separate clinical entity than emphysematous pyelonephritis because it has an excellent prognosis and is often considered benign. (Radiology 2001;218:647.) Gas that extends into the renal parenchyma is considered emphysematous pyelonephritis. Renal parenchymal gas can be focal or diffuse, and can spread via the collecting system into the perinephric and paranephric spaces.
Patients with emphysematous pyelonephritis often present with vague nonspecific symptoms including fever, abdominal or flank pain, vomiting, nausea, and dysuria. Patients with diabetes may report difficulty maintaining euglycemia. Patients may also present in fulminate septic shock or acute renal failure. Rarely they may complain of pneumaturia or have signs of crepitus on the flank. (Lancet 2001;357:194.)
Emphysematous pyelonephritis is a radiological diagnosis made by CT scan, abdominal radiograph, or renal ultrasound. CT scan is considered the definitive modality because of its ability to fully characterize the extent and position of gas within the kidney and collecting system and identify any tissue destruction. More than one radiological classification system is used for emphysematous pyelonephritis, but the one developed by Huang and Tseng (Arch Intern Med 2000;160:797) is most commonly used:
- Class I: Gas in collecting system only.
- Class II: Parenchymal gas only.
- Class IIIa: Extension of gas into perinephric space.
- Class IIIb: Extension of gas into pararenal space.
- Class IV: Emphysematous pyelonephritis in a solitary kidney or bilateral disease.
CT scan is also often used to monitor response to treatment. (Arch Intern Med 2000;160:797) The differential diagnosis of gas in the renal or ureteral system is limited. Instrumentation (e.g., cystoscopy) is a common cause of air in the urinary tract with renal laceration or trauma less common.
Treatment of patients with emphysematous pyelonephritis and septic shock should follow standard resuscitation protocols. Patients with comorbid diabetes should have their electrolytes aggressively monitored and treated. Patients with urinary obstruction and hydronephrosis should have the obstruction relieved (e.g., by stent or percutaneous nephrostomy drain). Nephrectomy was once the treatment of choice for patients with confirmed emphysematous pyelonephritis, but now growing evidence supports using conservative measures and treatment with early empiric intravenous antibiotics targeting Gram-negative bacteria, even in patients with bilateral emphysematous pyelonephritis and in septic shock. (BMC Nephrology 2002;3:10; Urol 2012;79:1281.) The treatment approach, either surgical (i.e., emergency nephrectomy vs. stent or nephrostomy tube) or nonsurgical, must be tailored to the patient's condition, severity of disease, and situation (e.g., obstruction vs. no obstruction). (Nat Rev Urol 2009;6:272.)
This patient responded well to conservative management with empiric intravenous antibiotics. Her sugars stabilized, and she was discharged with a plan for two weeks of oral antibiotics.
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