(See also Introduction to Urinary Tract Infections [UTIs] Introduction to Urinary Tract Infections (UTIs) Urinary tract infections (UTIs) can be divided into upper tract infections, which involve the kidneys (pyelonephritis), and lower tract infections, which involve the bladder (cystitis), urethra... read more .)
Reflux of infected urine into the renal pelvis is the usual mechanism. Causes include obstructive uropathy Obstructive Uropathy Obstructive uropathy is structural or functional hindrance of normal urine flow, sometimes leading to renal dysfunction (obstructive nephropathy). Symptoms, less likely in chronic obstruction... read more , struvite calculi, Urinary Calculi Urinary calculi are solid particles in the urinary system. They may cause pain, nausea, vomiting, hematuria, and, possibly, chills and fever due to secondary infection. Diagnosis is based on... read more and, most commonly, vesicoureteral reflux Vesicoureteral Reflux (VUR) Vesicoureteral reflux is retrograde passage of urine from the bladder back into the ureter and sometimes also into the renal collecting system, depending on severity. Reflux predisposes to urinary... read more (VUR).
Pathologically, there is atrophy and calyceal deformity with overlying parenchymal scarring. Chronic pyelonephritis may progress to chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more . Patients with chronic pyelonephritis may have residual foci of infection that may predispose to bacteremia Bacteremia Bacteremia is the presence of bacteria in the bloodstream. It can occur spontaneously, during certain tissue infections, with use of indwelling genitourinary or IV catheters, or after dental... read more or, among kidney transplant Kidney Transplantation Kidney transplantation is the most common type of solid organ transplantation. (See also Overview of Transplantation.) The primary indication for kidney transplantation is End-stage renal failure... read more 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 Urinary Calculi Urinary calculi are solid particles in the urinary system. They may cause pain, nausea, vomiting, hematuria, and, possibly, chills and fever due to secondary infection. Diagnosis is based on... read more ) and infection increase risk. The most common pathogens are Proteus mirabilis and Escherichia coli.
Symptoms and Signs
Symptoms and signs are often vague and inconsistent. Some patients have fever, flank or abdominal pain, malaise, or anorexia. In xanthogranulomatous pyelonephritis, a unilateral mass can usually be palpated.
Urinalysis and urine culture
Chronic pyelonephritis is suspected in patients with a history of recurrent urinary tract infections (UTIs) and acute pyelonephritis Acute pyelonephritis Bacterial urinary tract infections (UTIs) can involve the urethra, prostate, bladder, or kidneys. Symptoms may be absent or include urinary frequency, urgency, dysuria, lower abdominal pain... read more . 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 Urinalysis In patients with renal disorders, symptoms and signs may be nonspecific, absent until the disorder is severe, or both. Findings can be local (eg, reflecting kidney inflammation or mass), result... read more 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 Genitourinary TB Tuberculosis outside the lung usually results from hematogenous dissemination. Sometimes infection directly extends from an adjacent organ. Symptoms vary by site but generally include fever... read more .
In xanthogranulomatous pyelonephritis, urine cultures almost always grow P. mirabilis or E. coli. CT imaging is done to detect calculi Urinary Calculi Urinary calculi are solid particles in the urinary system. They may cause pain, nausea, vomiting, hematuria, and, possibly, chills and fever due to secondary infection. Diagnosis is based on... read more 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 Renal Cell Carcinoma Renal cell carcinoma (RCC) is the most common renal cancer. Symptoms can include hematuria, flank pain, a palpable mass, and fever of unknown origin (FUO). However, symptoms are often absent... read more ), 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.
Correction of the obstruction
Long-term antibiotic therapy
Sometimes nephrectomy, sometimes followed by renal transplantation
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 Hypertensive Emergencies A hypertensive emergency is severe hypertension with signs of damage to target organs (primarily the brain, cardiovascular system, and kidneys). Diagnosis is by blood pressure (BP) measurement... read more 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 Kidney Transplantation Kidney transplantation is the most common type of solid organ transplantation. (See also Overview of Transplantation.) The primary indication for kidney transplantation is End-stage renal failure... read more 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.