Approach
Histopathological diagnosis is definitive. However, biopsies are not performed routinely. A combination of a past history of vesicoureteral reflux (VUR) or prior surgery for obstruction, or recurrent urinary tract infections (UTIs), in conjunction with appropriate imaging studies are used to make a presumptive clinical diagnosis.
History
Past medical history of one of the following may be suggestive:
Renal surgery
UTIs
VUR
Renal stones.
Specific symptoms may include weight loss, chronic flank pain, nausea, vomiting, headache, malaise, fatigue, and cloudy urine.
Some patients are asymptomatic at presentation and have no past medical history.
Physical examination
Patients may have no physical findings indicative of chronic pyelonephritis.
Signs are rarely present until late in the course of the disease, when patients develop hypertension.
Laboratory evaluation
The following tests are recommended for all patients:
Dipstick urinalysis may show leukocytes, haematuria, or proteinuria and is typically the test of choice for screening of kidney disease. It may be normal in chronic kidney disease, so should be done in conjunction with serum creatinine, which reflects the severity of renal impairment. Estimated glomerular filtration rate (eGFR) can be calculated from a formula using age, serum creatinine, sex, and race, and is better at approximating more severe degrees of renal dysfunction.[28]
Urinary sediment may show leukocytes or, rarely, leukocyte casts. Pyuria is not a consistent finding.[13] Urine should be sent for culture to exclude infection for all patients. Urinary nitrites, if positive, can be an indicator of urine infections, but will be falsely negative with some gram-positive non-nitrite-producing bacteria.[29]
Full blood count (FBC) may show raised leukocytosis or normocytic, normochromic anaemia.
Electrolyte panel may demonstrate evidence of hyponatraemia, hyperkalaemia, or acidosis depending on the degree of renal tubular damage and, possibly, volume depletion. C-reactive protein (CRP) may be helpful as a marker for those patients with more severe chronic pyelonephritis.[30]
Imaging
The purpose of renal imaging is to exclude other causes of renal impairment. An abdominal/pelvic computed tomography (CT) scan usually gives the most information, especially if there is a question about what the diagnosis is. Ultrasound is often recommended if renal obstruction is suspected but not confirmed by CT. A kidney-ureter-bladder (KUB) x-ray is less useful than CT, but is a useful baseline investigation, and may show radio-opaque calcifications in the renal tract.
In children and infants with UTI, an aggressive approach to radiological evaluation is recommended due to the long-term effects of reflux on kidney structure and function. Imaging involves ultrasound and a voiding cystourethrogram.[11] Newer methods of detecting VUR have been developed, but which tests to use in which children is still being evaluated.[31]
Ultrasound is non-invasive and may exclude gross pathology, but further imaging is necessary to visualise the renal infrastructure.
Imaging studies such as CT and magnetic resonance imaging (MRI) are necessary to show evidence of scarred, shrunken kidneys. MRI and CT scanning have now replaced intravenous urography and technetium-99m dimercaptosuccinic acid (Tc-99m-DMSA) nuclear scintigraphy in diagnosis, providing more accurate imaging.[32]
CT is more cost-effective than MRI and helps to exclude other diagnoses.
If a patient is allergic to the contrast used in CT or further imaging of the renal system is needed or MRI is readily available, an MRI may be done.
Histopathology
For patients who are asymptomatic, without significant past medical history and with abnormalities detected on laboratory tests or imaging, a biopsy may be warranted to look for treatable causes of renal disease.
However, a renal biopsy is almost never used any more to make the diagnosis of chronic pyelonephritis, as imaging techniques have improved considerably and results of the biopsy do not alter treatment.
Xanthogranulomatous pyelonephritis (XGP)
May present with non-specific symptoms: fevers, malaise, fatigue, weight loss, and back or flank pain are common, making pre-operative diagnosis difficult.[25]
Laboratory evaluation may reveal persistent anaemia and leukocytosis.
Urine cultures are often positive for Proteus (60%), or less often for E coli, Klebsiella, Staphylococcus aureus, or mixed organisms. Imaging studies may demonstrate an enlarged kidney with calculi and a mass that is often indistinguishable from a tumour.[33] For this reason, XGP is often misdiagnosed pre-operatively.[8] CT or MRI scans are the imaging studies most often used to delineate the extent of the disease.[33] Ultrasound can be used to demonstrate renal stones and obstruction.[34] Definitively diagnosed from histopathological examination following nephrectomy.[33][35]
Emphysematous pyelonephritis (EPN)
Patients are acutely ill, often with the classic signs of acute pyelonephritis (i.e., fever, back or flank pain, nausea or vomiting, malaise); a sub-set may be severely ill with sepsis or impending sepsis. Patients usually have an elevated white blood cell count and abnormal urinalysis results. CRP can be significantly raised in patients with EPN.[36] Because most people with EPN live with diabetes mellitus, blood glucose levels are often elevated. Urine cultures and blood cultures may be positive for E coli, Klebsiella, or Proteus infections. Plain x-rays show gas in the renal collecting system and parenchyma.[37] CT or MRI scans are the imaging studies most often used to delineate the extent of the disease.[1] Ultrasound may show air within the renal parenchyma.[34]
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