Histopathological diagnosis is definitive BEST PRACTICE

Step-by-step diagnostic approach

Histopathological diagnosis is definitive. However, biopsies are not performed routinely. A combination of a past history of vesicoureteral reflux or prior surgery for obstruction, recurrent UTIs, in conjunction with appropriate imaging studies are used to make a presumptive clinical diagnosis.

History

Past medical history of one the following may be suggestive:

• Renal surgery
• UTIs
• Vesicoureteral reflux
• Renal stones.

Specific symptoms may include weight loss, chronic flank pain, nausea, vomiting, headache, malaise, weight loss, 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 HTN.

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 GFR (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. [21]
• Urinary sediment may show leukocytes or, rarely, leukocyte casts. Pyuria is not a consistent finding. [9] 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. [22]
• 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. CRP may be helpful as a marker for those patients with more severe chronic pyelonephritis. [23]

Imaging

The purpose of renal imaging is to exclude other causes of renal impairment. An abdominal/pelvic 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 KUB (kidney-ureter-bladder) 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. [7]

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 MRI are necessary to show evidence of scarred, shrunken kidneys. MRI and CT scanning have now replaced IV urography and Tc-99m-DMSA nuclear scintigraphy in diagnosis, providing more accurate imaging. [24]

CT is more cost-effective than MRI and helps 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 those 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 anymore 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 preoperative diagnosis difficult. [19]

Laboratory evaluation may reveal persistent anaemia and leukocytosis.

Urine cultures are often positive for Proteus (60%), or less often for E coli, Klebsiella, S aureus, or mixed organisms. Imaging studies may demonstrate an enlarged kidney with calculi and a mass that is often indistinguishable from a tumour. [25] For this reason, XGP is often misdiagnosed preoperatively. [6] CT or MRI scans are the imaging studies most often used to delineate the extent of the disease. [25] Ultrasound can be used to demonstrate renal stones and obstruction. [26] Definitively diagnosed from histopathological examination following nephrectomy. [25] [27]

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 WBC count and abnormal urinalysis results. CRP can be significantly raised in patients with EPN. [28] Because most are diabetic, blood glucose levels often are 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. [29] 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. [26]

http://bestpractice.bmj.com/best-practice/monograph/552/diagnosis/guidelines.html