Pyelonephritis classification

Pyelonephritis is an upper urinary tract infection. Pyelonephritis may be classified according to the duration of disease and etiology into 5 subtypes: acute uncomplicated, acute complicated, chronic, emphysematous, and xanthogranulomatous pyelonephritis. Most cases of Pyelonephritis are acute uncomplicated and occur in normal healthy individuals with no history of a structural urinary tract anomaly or any long-term disease. Classification of pyelonephritis helps understand dynamics and specify treatments according to the duration, severity and the type of pyelonephritis.

There are five different types of pyelonephritis:^{[1][2][3][4][5][6][7]}

• Acute Uncomplicated Pyelonephritis

• Acute pyelonephritis is a common clinical diagnosis in normally healthy patients who present with fever, chills, and flank tenderness.^[8][9]
• Infections typically result from ascending retrograde spread through the collecting ducts into the renal parenchyma.
• Patients are referred for CT evaluation of acute pyelonephritis when symptoms are poorly localized or complications are suspected.

• Acute Complicated Pyelonephritis

• Acute complicated Pyelonephritis is the type that occurs in patients with known structural abnormalities of the urinary tract, pregnant or post menopausal women or in the presence of a disease like diabetes.
• Acute complicated pyelonephritis requires a prolong duration of broad spectrum antibiotics.
• CT scan is used for confirmation and for detection of complications.

• Chronic Pyelonephritis

• Chronic pyelonephritis is a somewhat controversial disease from a pathogenetic standpoint. It is unclear that, whether it is an active chronic infection, arises from multiple recurrent infections, or represents stable changes from a remote single infection.
• Hypertension is frequently a long-term sequela and so is an iliopsoas abscess.

• Emphysematous Pyelonephritis

• Emphysematous pyelonephritis represents a severe life-threatening infection (overall mortality rate of approximately 50%) of the renal parenchyma with gas-forming bacteria.
• Underlying poorly controlled diabetes mellitus is present in up to 90% of patients who develop emphysematous pyelonephritis.
• Patients present clinically with varying degrees of renal failure, lethargy, acid-base imbalances, and hyperglycemia.
• E coli is the causative bacterial source in approximately 70% of cases.
• It can be further divided into type 1 and 2 depending on presence of fluid and pattern of gas accumulation.

• Xanthogranulomatous Pyelonephritis

• Xanthogranulomatous pyelonephritis (XGP) is a rare inflammatory condition usually secondary to chronic obstruction caused by nephrolithiasis and resulting in infection and irreversible destruction of the renal parenchyma.
• XGP is associated with a staghorn calculus in approximately 70% of cases.
• Patients with diabetes are particularly predisposed to the formation of XGP.
• Treatment is nephrectomy.
• At histologic analysis, the inflammatory mass is composed of lipid-laden macrophages and chronic inflammatory cells.

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