Pyelonephritis

Analysis of the urine may show signs of urinary tract infection. Specifically, the presence of nitrite and white blood cells on a urine test strip in patients with typical symptoms are sufficient for the diagnosis of pyelonephritis, and are an indication for empirical treatment. Blood tests such as a complete blood count may show neutrophilia. Microbiological culture of the urine, with or without blood cultures and antibiotic sensitivity testing are useful for establishing a formal diagnosis,[9] and are considered mandatory.[15]

If a kidney stone is suspected (e.g. on the basis of characteristic colicky pain or the presence of a disproportionate amount of blood in the urine), a kidneys, ureters, and bladder x-ray (KUB film) may assist in identifying radioopaque stones.[9] Where available, a noncontrast helical CT scan with 5 millimeter sections is the diagnostic modality of choice in the radiographic evaluation of suspected nephrolithiasis.[16][17][18] All stones are detectable on CT scans except very rare stones composed of certain drug residues in the urine.[19] In patients with recurrent ascending urinary tract infections, it may be necessary to exclude an anatomical abnormality, such as vesicoureteral reflux or polycystic kidney disease. Investigations used in this setting include kidney ultrasonography or voiding cystourethrography.[9] CT scan or kidney ultrasonography is useful in the diagnosis of xanthogranulomatous pyelonephritis; serial imaging may be useful for differentiating this condition from kidney cancer.[10]

Acute pyelonephritis with increased cortical echogenicity and blurred delineation of the upper pole.[20]

Ultrasound findings that indicate pyelonephritis are enlargement of the kidney, edema in the renal sinus or parenchyma, bleeding, loss of corticomedullary differentiation, abscess formation, or an areas of poor blood flow on doppler ultrasound.[21] However, ultrasound findings are seen in only 20% to 24% of people with pyelonephritis.[21]

A DMSA scan is a radionuclide scan that uses dimercaptosuccinic acid in assessing the kidney morphology. It is now the most reliable test for the diagnosis of acute pyelonephritis.[22]

Acute pyelonephritis is an exudative purulent localized inflammation of the renal pelvis (collecting system) and kidney. The kidney parenchyma presents in the interstitium abscesses (suppurative necrosis), consisting in purulent exudate (pus): neutrophils, fibrin, cell debris and central germ colonies (hematoxylinophils). Tubules are damaged by exudate and may contain neutrophil casts. In the early stages, the glomerulus and vessels are normal. Gross pathology often reveals pathognomonic radiations of bleeding and suppuration through the renal pelvis to the renal cortex.

Chronic pyelonephritis implies recurrent kidney infections and can result in scarring of the renal parenchyma and impaired function, especially in the setting of obstruction. A perinephric abscess (infection around the kidney) and/or pyonephrosis may develop in severe cases of pyelonephritis.[23]

• Abscess around both kidneys[24]
• Abscess around both kidneys[24]
• 
  Chronic pyelonephritis with reduced kidney size and focal cortical thinning. Measurement of kidney length on the US image is illustrated by ‘+’ and a dashed line.[20]

Xanthogranulomatous pyelonephritis is an unusual form of chronic pyelonephritis characterized by granulomatous abscess formation, severe kidney destruction, and a clinical picture that may resemble renal cell carcinoma and other inflammatory kidney parenchymal diseases. Most affected individuals present with recurrent fevers and urosepsis, anemia, and a painful kidney mass. Other common manifestations include kidney stones and loss of function of the affected kidney. Bacterial cultures of kidney tissue are almost always positive.[25] Microscopically, there are granulomas and lipid-laden macrophages (hence the term xantho-, which means yellow in ancient Greek). It is found in roughly 20% of specimens from surgically managed cases of pyelonephritis.[10]

A 2018 systematic review recommended the use of norfloxacin as it has the lowest rate of side effects with a comparable efficacy to commonly used antibiotics.[29]

In people who do not require hospitalization and live in an area where there is a low prevalence of antibiotic-resistant bacteria, a fluoroquinolone by mouth such as ciprofloxacin or levofloxacin is an appropriate initial choice for therapy.[5] In areas where there is a higher prevalence of fluoroquinolone resistance, it is useful to initiate treatment with a single intravenous dose of a long-acting antibiotic such as ceftriaxone or an aminoglycoside, and then continuing treatment with a fluoroquinolone. Oral trimethoprim/sulfamethoxazole is an appropriate choice for therapy if the bacteria is known to be susceptible.[5] If trimethoprim/sulfamethoxazole is used when the susceptibility is not known, it is useful to initiate treatment with a single intravenous dose of a long-acting antibiotic such as ceftriaxone or an aminoglycoside. Oral beta-lactam antibiotics are less effective than other available agents for treatment of pyelonephritis.[15] Improvement is expected in 48 to 72 hours.[5]

People with acute pyelonephritis that is accompanied by high fever and leukocytosis are typically admitted to the hospital for intravenous hydration and intravenous antibiotic treatment. Treatment is typically initiated with an intravenous fluoroquinolone, an aminoglycoside, an extended-spectrum penicillin or cephalosporin, or a carbapenem. Combination antibiotic therapy is often used in such situations. The treatment regimen is selected based on local resistance data and the susceptibility profile of the specific infecting organism(s).[15]

During the course of antibiotic treatment, serial white blood cell count and temperature are closely monitored. Typically, the intravenous antibiotics are continued until the person has no fever for at least 24 to 48 hours, then equivalent antibiotics by mouth can be given for a total of two–week duration of treatment.[30] Intravenous fluids may be administered to compensate for the reduced oral intake, insensible losses (due to the raised temperature) and vasodilation and to optimize urine output. Percutaneous nephrostomy or ureteral stent placement may be indicated to relieve obstruction caused by a stone. Children with acute pyelonephritis can be treated effectively with oral antibiotics (cefixime, ceftibuten and amoxicillin/clavulanic acid) or with short courses (2 to 4 days) of intravenous therapy followed by oral therapy.[31] If intravenous therapy is chosen, single daily dosing with aminoglycosides is safe and effective.[31]

Fosfomycin can be used as an efficacious treatment for both UTIs and complicated UTIs including acute pyelonephritis. The standard regimen for complicated UTIs is an oral 3g dose administered once every 48 or 72 hours for a total of 3 doses or a 6 grams every 8 hours for 7 days to 14 days when fosfomycin is given in IV form.[32]

Treatment of xanthogranulomatous pyelonephritis involves antibiotics as well as surgery. Removal of the kidney is the best surgical treatment in the overwhelming majority of cases, although polar resection (partial nephrectomy) has been effective for some people with localized disease.[10][33] Watchful waiting with serial imaging may be appropriate in rare circumstances.[34]

If no improvement is made in one to two days post therapy, inpatients should repeat an urine analysis and imaging. Outpatients should check again with their doctor.[35]