Practice Essentials
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]
Signs and symptoms
Typical presenting features of EPN include the following:
-
Fever (79%)
-
Abdominal or flank pain (71%)
-
Nausea and vomiting (17%)
-
Dyspnea (13%)
-
Acute kidney injury (35%)
-
Altered sensorium (19%)
-
Shock (29%)
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 [3]
-
Comorbidities include alcoholism, malnourishment, renal calculi, and diabetic ketoacidosis
See Presentation for more detail.
Diagnosis
Laboratory findings include the following:
-
Leukocytosis with a left shift
-
Pyuria
-
Infected urine
-
Thrombocytopenia
-
An elevated creatinine level
-
Positive blood culture results
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 (KUB) 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 [4] :
-
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.
Management
Conservative treatment is indicated in the following situations:
-
Patients with compromised kidney 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:
-
Prompt hydration
-
Fluid resuscitation
-
Systemic antibiotics
-
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 compromised kidney function, doses must be adjusted according to creatinine clearance
Nephrectomy is indicated as follows:
-
Treatment of choice for most patients [5]
-
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)
See Treatment and Medication for more detail.
For patient education information, see Kidney Infection (Pyelonephritis).
Background
A case of pneumaturia was reported in 1671. [1] Kelly and MacCullum reported the first case of gas-forming kidney infection in 1898. [6] Historicallly, EPN has been described by terms such as renal emphysema and pneumonephritis; Schultz and Klorfein recommended the term emphysematous pyelonephritis in 1962. [7]
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. [7]
Pathophysiology
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. [8] Analyses of the gas content in EPN have 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. [9, 10]
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.
Etiology
EPN is typically caused by enteric gram-negative facultative anaerobes. [11] 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.
A case of EPN complicated by methicillin-resistant Staphylococcus aureus (MRSA) has been reported. [12]
Rarely, fungi (eg, Aspergillus fumigatus, Candida species) and protozoa (Entamoeba histolytica) have been isolated in patients with EPN. [13, 2, 14]
Epidemiology
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 glucose. 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. [15]
Rare cases have been reported in persons who do not have diabetes, with kidney failure and immunosuppression as contributing factors. Of those patients, 22% have obstructed upper tracts, 4% have polycystic kidneys, and 4% have end-stage kidney disease. Obstruction is the main cause of EPN in persons without diabetes. EPN has been reported in transplanted kidneys. [16, 17]
The left kidney is affected more commonly than the right. Bilateral cases have also been reported.
Prognosis
Untreated cases of 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%. [4] 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. [18] The presence of thrombocytopenia, acute kidney injury, hypoalbuminemia, and septic shock at presentation also confers poor prognosis. [19] Comorbid diabetic ketoacidosis, although rare, is associated with high mortality. [20]
In a series of 68 cases, high leukocyte and lymphocyte counts were the main risk factors for urosepsis but were not associated with higher risk of mortality on multivariate regression analysis. [21]
Risk of mortality is higher in patients treated with antibiotics alone than in those who receive additional interventions such as percutaneous drainage of the abscess. [22] EPN that receives medical treatment only may progress to uncontrollable sepsis that requires surgical intervention. Perinephric abscess and kidney failure are other possible complications.
A number of risk scores have been proposed to predict at presentation those patients with the highest risk for mortality. In 2024, Trujillo-Santamaría and colleagues published a mortality risk score based on the following clinical and laboratory findings [23] :
-
Quick Sepsis-related Organ Failure Assessment score ≥2 (2 points)
-
Anemia (1 point)
-
Paranephric gas extension (1 point)
-
Leukocyte count > 22,000/μL (1 point)
-
Thrombocytopenia (1 point)
-
Hyperglycemia (1 point)
The score was developed with 400 patients from 15 centers and validated with 170 patients from 7 centers. The mortality rates were as follows:
-
< 5% for scores ≤3
-
36% for a score of 4
-
63% for a score of 5
-
83% for a score of 6
-
100% for a score of 7
-
Kidneys, ureter, and bladder imaging showing a streaky gas pattern over the entire right kidney in a patient with emphysematous pyelonephritis.
-
Emphysematous pyelonephritis. Kidneys, ureter, and bladder imaging showing gas over the region of the right kidney. White arrows outline the area. The faint outline of a staghorn calculus can be seen in the right kidney.
-
Emphysematous pyelonephritis. Renal sonogram showing hyperechoic shadows suggestive of gas along the lower pole of the kidney.
-
Emphysematous pyelonephritis. CT scan showing gas in the left kidney, with stones and xanthogranulomatous pyelonephritis.
-
CT scan showing right renal and perinephric gas in a patient with emphysematous pyelonephritis.
-
CT scan showing gas in both kidneys and the inferior vena cava in a patient with bilateral emphysematous pyelonephritis.
-
Algorithm for the management of emphysematous pyelonephritis.
