Background

A 56-year-old man with a history of hepatitis C and diabetes mellitus presents to the emergency department (ED) with right flank pain and subjective fevers of 2-3 days’ duration. The patient describes his pain as being mild in intensity but constant and nonradiating, with a pressure-like quality. The patient takes 20 units of neutral protamine Hagedorn (NPH) insulin injected subcutaneously twice daily for his diabetes, but he states that his self-reported daily blood glucometer readings have been approximately 250-350 mg/dL for the past month.

{mosimage}On physical examination, the patient’s vital signs are a blood pressure of 100/60 mm Hg, a heart rate of 96 bpm, a respiratory rate of 16 breaths/min, and an oral temperature of 102.2°F (39.0°C). The cardiac and respiratory portions of the examination are unremarkable. The patient is noted to have tenderness in the right costovertebral angle. His abdominal examination is unremarkable for any tenderness to palpation, rebound, or guarding.

Clinically significant laboratory results include a white blood cell (WBC) count of 24.4 × 109/L, a blood urea nitrogen (BUN) concentration of 71 mg/dL, a creatinine level of 5.4 mg/dL, and a serum glucose level 629 mg/dL. The urinalysis reveals cloudy urine with copious WBCs, a glucose concentration of 100 mg/dL, a protein concentration of 100 mg/dL, and a large leukocyte esterase.

Renal ultrasonography is performed and reveals an abnormality of the right kidney (see Images 1-2). To further illustrate this abnormality, an abdominal computed tomography (CT) scan was obtained (see Image 3).

What is the diagnosis?

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Hint

This condition most commonly occurs in patients with diabetes.
Authors:
Pramod Gupta, MD, Staff Physician, Department of Radiology, Dallas VA Medical Center, Dallas, Texas

Nahid Eshaghi, MD, Acting Chief of Radiology, Dallas VA Medical Center, Texas

eMedicine Editors:
Erik D. Schraga, MD, Department of Emergency Medicine, Kaiser Permanente, Santa Clara Medical Center, CA

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Answer

{mosimage}Emphysematous pyelonephritis (EPN): Sonograms of the right kidney (see Images 1-2) show several hyperechoic foci (arrows) in the upper pole, with dirty acoustic shadowing (arrowheads). These findings are suggestive of gas in the renal parenchyma. Nonenhanced CT scans (see Image 3) confirmed the abnormalities noted on the sonograms by clearly demonstrating air in the renal parenchyma (arrows). These radiographic findings were consistent with a diagnosis of EPN. Several small calculi are also incidentally noted in the gallbladder (arrowheads).

EPN is a rare, life-threatening, necrotizing infection of the renal parenchyma and perirenal tissues caused by pathogenic gas-forming bacteria. The primary organisms that cause this condition are Escherichia coli (66 %), Klebsiella species (26%), and Proteus (<10%) species, and they can be routinely identified on urine cultures. The vast majority of patients with EPN have underlying, poorly controlled diabetes mellitus. The remaining patients usually have obstructive uropathy, papillary necrosis, or clinically significant functional impairment.

The pathogenesis of EPN is poorly understood. Some authors suggest that high glucose concentrations allow organisms such as E coli to proliferate and produce carbon dioxide; however, this reasoning does not account for the infrequency of EPN despite the regularity of urinary infections in patients with diabetes. The disease is most likely an advanced form of pyelonephritis rather than a specific and unique clinical entity. Furthermore, the pathogenesis of EPN is likely multifactorial in distinction to the etiology of an acute kidney infection—a condition that occurs in otherwise healthy patients or in patients with clearly identifiable risk factors, such as structural or functional alterations in the urinary tract or an underlying immunodeficiency state.

EPN is usually unilateral, with only 5-7% of cases occurring bilaterally. All known cases of EPN have occurred in adults. The clinical presentation resembles that of acute pyelonephritis, with fever, chills, flank pain, nausea, vomiting, and dysuria. Patients may present with sepsis, confusion, lethargy, or coma (in advanced disease). The diagnosis of EPN is typically considered only after treatment for suspected pyelonephritis fails, as the lack of distinct clinical manifestations conceals the condition’s presence.

Because EPN cannot be identified on the basis of clinical findings alone, the diagnosis must be verified with radiographic findings. Plain abdominal radiographs may show gas in or around the affected kidney; however, the inability of this imaging modality to differentiate renal gas from overlying bowel gas may preclude a definitive interpretation of the results. Ultrasonography characteristically shows distinctly echogenic areas in the renal parenchyma and perinephric tissues, often with low-level dirty acoustic shadowing in the posterior aspects. Because of potentially diffuse shadowing caused by gas, the depth of parenchymal involvement may be underestimated, and renal calculi may be obscured. CT is the preferred imaging modality for a definitive diagnosis of EPN. CT scanning can also define the presence of renal calculi and the extent of infection.

A classification scheme based on CT findings divides EPN into types I and II, each with different prognostic implications. Type I EPN is characterized by parenchymal destruction, with streaky or mottled gas collections and an absence of fluid collections. Type II EPN is distinguished by bubbly or loculated gas in the parenchyma or collecting system, with associated renal or perirenal fluid. These fluid collections are thought to represent a favorable immune response consisting of exudates and inflammatory cells. Type I EPN is associated with significantly increased mortality, approaching 70%, as compared with 18% for type II EPN.

First-line treatment for EPN includes aggressive fluid support, correction of electrolyte and acid-base irregularities, hyperglycemic control, and intravenous administration of broad-spectrum antibiotics. Subsequent therapy is focused not only on relief of any obstruction of the affected kidney to preserve remaining function, but also on possible percutaneous drainage of any fluid collections in the affected kidney. Despite aggressive therapy, many patients have a fulminant clinical course, unsuccessful drainage, or failed conservative therapy. These patients may require an urgent nephrectomy. The patient in this case responded to medical management with intravenous antibiotics and was discharged home after a prolonged hospitalization.

References:

Dahnert W. Radiology Review Manual. Philadelphia, Pa: Lippincott, Williams and Wilkins; 1999:788-89.
Grayson DE, Abbott RM, Levy AD, Sherman PM. Emphysematous infections of the abdomen and pelvis: a pictorial review. adiographics 2002 May-Jun;22:543-61. Review. [MEDLINE: 12006686]
Schaeffer AJ. Emphysematous pyelonephritis. In: Walsh PC, Retik AB, Vaughan ED Jr, et al: Campbell’s Urology. 8th ed, Philadelphia, Pa: W.B. Saunders; 2002:556-8.
Shetty S. Emphysematous pyelonephritis. eMedicine Journal [series online]. Last updated: Feb. 2006. Available at: http://www.emedicine.com/med/topic3440.htm.

Rick G. Kulkarni, MD, FACEP, Assistant Professor, Yale School of Medicine, Section of Emergency Medicine, Department of Surgery, Attending Physician, Medical Director, Department of Emergency Services, Yale-New Haven Hospital, CT