(See also Introduction to Urinary Tract Infections [UTIs].)
Pathologically there is atrophy and calyceal deformity with overlying parenchymal scarring. Chronic pyelonephritis may progress to chronic kidney disease. Patients with chronic pyelonephritis may have residual foci of infection that may predispose to bacteremia or, among kidney transplant patients, seed the urinary tract and transplanted kidney.
Xanthogranulomatous pyelonephritis (XPN) is an unusual variant that appears to represent an abnormal inflammatory response to infection. Giant cells, lipid-laden macrophages, and cholesterol clefts account for the yellow color of the infected tissue. The kidney is enlarged, and perirenal fibrosis and adhesions to adjacent retroperitoneal structures are common. The disorder is almost always unilateral and most often occurs in middle-aged women with a history of recurrent UTIs. Long-term urinary tract obstruction (usually by a calculus) and infection increase risk. The most common pathogens are Proteus mirabilis and Escherichia coli.
Chronic pyelonephritis is suspected in patients with a history of recurrent urinary tract infections (UTIs) and acute pyelonephritis. However, most patients, except for children with vesicoureteral reflux (VUR), do not have such a history. Sometimes the diagnosis is suspected because typical findings are incidentally noted on an imaging study. Symptoms, because they are vague and nonspecific, may not suggest the diagnosis.
Urinalysis and urine culture and usually imaging tests are done. Urinary sediment is usually scant, but renal epithelial cells, granular casts, and occasionally white blood cell (WBC) casts are present. Proteinuria is almost always present and can be in the nephrotic range if VUR causes extensive renal damage. When both kidneys are involved, defects in concentrating ability and hyperchloremic acidosis may appear before significant azotemia occurs. Urine culture may be sterile or positive, usually for gram-negative organisms.
Initial imaging is usually with ultrasonography, helical CT, or intravenous urography (IVU). The hallmark of chronic pyelonephritis (usually with reflux or obstruction) on imaging is classically a large, deep, segmental, coarse cortical scar usually extending to one or more of the renal calyces. The upper pole is the most common site. Renal cortex is lost, and the renal parenchyma thins. Uninvolved renal tissue may hypertrophy locally with segmental enlargement. Ureteral dilation may be present, reflecting the changes induced by chronic severe reflux. Similar changes can occur with urinary tract tuberculosis.
In XPN, urine cultures almost always grow P. mirabilis or E. coli. CT imaging is done to detect calculi or other obstruction. Imaging shows an avascular mass with a variable degree of extension around the kidney. Sometimes, to differentiate cancer (eg, renal cell carcinoma), biopsy may be required, or tissue removed during nephrectomy can be examined.
The course of chronic pyelonephritis is extremely variable, but the disease typically progresses very slowly. Most patients have adequate renal function for ≥20 years after onset. Frequent exacerbations of acute pyelonephritis, although controlled, usually further deteriorate renal structure and function. Continued obstruction predisposes to or perpetuates pyelonephritis and increases intrapelvic pressure, which damages the kidney directly.
If obstruction cannot be eliminated and recurrent urinary tract infections are common, long-term therapy with antibiotics (eg, trimethoprim/sulfamethoxazole, trimethoprim, a fluoroquinolone, nitrofurantoin) is useful and may be required indefinitely. Complications of uremia or hypertension must be treated appropriately.
For xanthogranulomatous pyelonephritis, an initial course of antibiotics should be given to control local infection, followed by en bloc nephrectomy with removal of all involved tissue.
Patients undergoing renal transplantation who have chronic pyelonephritis may require nephrectomy before the transplant.
Chronic pyelonephritis usually affects patients predisposed to urinary reflux into the renal pelvis (eg, by VUR, obstructive uropathy, or struvite calculi).
Suspect chronic pyelonephritis if patients have recurrent acute pyelonephritis, but the diagnosis is often first suspected based on incidental findings on imaging.
Obtain an imaging study (ultrasonography, helical CT, or intravenous urography [IVU]).
If obstruction cannot be relieved, consider long-term antibiotic prophylaxis.