Emphysematous Pyelonephritis (EPN)
Emphysematous pyelonephritis (EPN) is a severe infection of the renal parenchyma that causes gas accumulation in the tissues (see the image below). EPN most often occurs in persons with diabetes mellitus, especially women. Its presentation is similar to that of acute pyelonephritis, but EPN often has a fulminating course, and can be fatal if not recognized and treated promptly. [1, 2]
Typical presenting features of EPN include the following:
Abdominal or flank pain (71%)
Nausea and vomiting (17%)
Acute renal impairment (35%)
Altered sensorium (19%)
Other possible findings include the following:
Crepitus over the flank area may occur in advanced cases of EPN
Pneumaturia is uncommon unless emphysematous cystitis is present
Subcutaneous emphysema and pneumomediastinum have been reported 
Comorbidities include alcoholism, malnourishment, renal calculi, and diabetic ketoacidosis
See Presentation for more detail.
Laboratory findings include the following:
Leukocytosis with a left shift
An elevated creatinine level
Positive blood culture results
Computed tomography (CT) scanning is the definitive imaging test for EPN. CT may show the following:
Gas patterns that are streaky, streaky and mottled, or streaky and bubbly
Rimlike or crescent-shaped gas collections in the perinephric area
Gas in the renal vein or inferior vena cava and along the psoas muscle
Perinephric abscess may lead to significant gas accumulation in the perinephric space
A stone may be seen in the collecting system
Other imaging study findings are as follows:
Kidneys, ureter, and bladder imaging often reveals gas distribution over the region of the kidneys
Renal ultrasonograms often reveal high echogenic areas with dirty shadowing
Several different staging systems for EPN have been suggested. A system proposed by Michaeli et al and modified by Huang and Tseng is as follows  :
Class 1: Gas confined to the collecting system
Class 2: Gas confined to the renal parenchyma alone
Class 3A: Perinephric extension of gas or abscess
Class 3B: Extension of gas beyond the Gerota fascia
Class 4: Bilateral EPN or EPN in a solitary kidney
See Workup for more detail.
Conservative treatment is indicated in the following situations:
Patients with compromised renal function
Early cases associated with gas in the collecting system alone, and patient is in otherwise stable condition
Class 1 and class 2 EPN
Class 3 and class 4 EPN: In the presence of fewer than 2 risk factors (eg, thrombocytopenia, elevated serum creatinine levels, altered sensorium, shock)
Conservative treatment consists of the following:
Relief of obstruction with percutaneous drainage or stent placement
Rapid control of diabetes, if present
Initial antibiotic therapy should target gram-negative bacteria and should take into account individual patient characteristics and local patterns of antibiotic resistance. In patients with renal compromise, doses must be adjusted according to creatinine clearance
Nephrectomy is indicated as follows:
Treatment of choice for most patients
No access to percutaneous drainage or internal stenting (after patient is stabilized)
Gas in the renal parenchyma or “dry-type” EPN
Possibly bilateral nephrectomy in patients with bilateral EPN
Class 3 and class 4 EPN: In the presence of more than 2 risk factors (eg, thrombocytopenia, elevated serum creatinine, altered sensorium, shock)
For patient education resources, see Urinary Tract Infections.
A case of pneumaturia was reported in 1671.  Kelly and MacCullum reported the first case of gas-forming renal infection in 1898.  Historicallly, EPN has been described by terms such as renal emphysema and pneumonephritis; Schultz and Klorfein recommended the term emphysematous pyelonephritis in 1962. 
The mortality rate associated with EPN was high before the advent of antibiotics. Advances in imaging technology, control of diabetes, resuscitative management, and minimally invasive treatment have improved the outcome in patients with EPN.
Until the late 1980s, emergency nephrectomy and/or open surgical drainage plus antibiotics was the accepted treatment for EPN. Since then, however, a nephron-sparing approach has gradually gained preference for less-severe cases. Percutaneous catheter drainage has demonstrated good success with low mortality, although some patients do require subsequent nephrectomy. 
EPN is a severe infection of the renal parenchyma that causes gas accumulation in the tissues. The infection often has a fulminating course and can be fatal if left untreated. However, urinary tract infections are common in persons with diabetes, and not all of these infections lead to EPN. The factors that predispose to EPN in persons with diabetes may include uncontrolled diabetes, high levels of glycosylated hemoglobin, and impaired host immune mechanisms.
Fermentation of glucose with carbon dioxide production by the pathogens has been proposed as the cause of gas in the tissues. Schainuck et al proposed that fermentation products from tissue necrosis produced carbon dioxide.  Three analyses of the gas content din EPN demonstrated that the major components include nitrogen (60%), hydrogen (15%), carbon dioxide (5%), and oxygen (8%). Huang et al concluded that mixed acid fermentation is the mechanism of gas production, based on the presence of hydrogen. [8, 9]
Although carbon dioxide is released by the bacteria, the final tissue equilibrium achieved by tissues and gas bubbles determines the final carbon dioxide content. Diabetic microangiopathy may also contribute to the slow transport of catabolic products and may lead to accumulation of gas.
Emphysematous pyelonephritis (EPN) is typically caused by enteric gram-negative facultative anaerobes.  Escherichia coli is isolated in 66% of patients, and Klebsiella species are reported in 26% of patients. Proteus,Pseudomonas, and Streptococcus species are other organisms found in patients with EPN. Mixed organisms are observed in 10% of patients. Positive blood culture results are identical to urine culture results in 54% of patients.
Emphysematous pyelonephritis (EPN) is a rare condition. Only 1-2 cases per year are encountered in a typical busy urologic department in the United States. However, the frequency of reports from developing nations suggests that this may be a reflection of access to health care and health education.
The mean age of patients with EPN is reportedly 55 years, with a range of 19-81 years. The condition is 6 times more common in women. Ninety-five percent of patients have diabetes. In most patients, the diabetes is uncontrolled, with high levels of glycosylated hemoglobin (72%) or of blood sugar. Because the condition preferentially affects persons with diabetes, the reported frequency reflects how poorly diabetes is controlled in these geographical areas. Renal stones are another predisposing condition and therefore affect the frequency of EPN.
Rare cases have been reported in persons who do not have diabetes, with renal failure and immunosuppression as contributing factors. Of these patients, 22% have obstructed upper tracts, 4% have polycystic kidneys, and 4% have end-stage renal disease. Obstruction is the main cause of EPN in persons without diabetes. EPN has been reported in transplanted kidneys. [13, 14]
The left kidney is affected more commonly than the right. Bilateral cases have also been reported.
Untreated cases of emphysematous pyelonephritis (EPN) result in death. The mortality rate associated with the disease was high before the advent of antibiotics; however, advances in imaging technology, diabetes control, resuscitative management, and minimally invasive treatment have improved patient outcomes.
Huang and Tseng reported an overall EPN mortality rate of 19%.  They also reported significant treatment success rates with percutaneous drainage and antibiotics (66%) and with nephrectomy (90%).
Factors associated with a poor prognosis in patients with EPN include altered level of consciousness, multiple organ failure, hyperglycemia, and leukocytosis. 
EPN that receives only medical treatment may lead to uncontrollable sepsis that requires surgical intervention. Perinephric abscess and renal failure are other possible complications.
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Sugandh Shetty, MD, FRCS Associate Professor of Urology, Oakland University William Beaumont School of Medicine; Attending Physician, Department of Urology, William Beaumont Hospital
Sugandh Shetty, MD, FRCS is a member of the following medical societies: American Urological Association
Disclosure: Nothing to disclose.
Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Ajay K Singh, MB, MRCP, MBA Associate Professor of Medicine, Harvard Medical School; Director of Dialysis, Renal Division, Brigham and Women’s Hospital; Director, Brigham/Falkner Dialysis Unit, Faulkner Hospital
Disclosure: Nothing to disclose.
Edward David Kim, MD, FACS Professor of Surgery, Division of Urology, University of Tennessee Graduate School of Medicine; Consulting Staff, University of Tennessee Medical Center
Edward David Kim, MD, FACS is a member of the following medical societies: American College of Surgeons, American Society for Reproductive Medicine, American Society of Andrology, American Urological Association, Sexual Medicine Society of North America, Tennessee Medical Association
Disclosure: Serve(d) as a speaker or a member of a speakers bureau for: Endo, Avadel.
Emphysematous Pyelonephritis (EPN)
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