ACUTE PYELONEPHRITIS

Acute pyelonephritis
A clinical diagnosis based on the presence of fever, flank pain, and tenderness, often with an elevated white count. It may affect one or both kidneys. There are usually accompanying symptoms suggestive of a lower UTI (frequency, urgency, suprapubic pain, urethral burning or pain on voiding) responsible for the ascending infection which resulted in the subsequent acute pyelonephritis. Nausea and vomiting are common.

Differential diagnosis
includes cholecystitis, pancreatitis, diverticulitis, appendicitis.

Risk factors
vesicoureteric reflux (VUR); urinary tract obstruction; calculi; spinal cord injury (neuropathic bladder); diabetes mellitus; congenital malformation; pregnancy; indwelling catheters.

Pathogenesis and microbiology
initially, there is patchy infiltration of neutrophils and bacteria in the parenchyma. Later changes include the formation of inflammatory bands extending from renal papilla to cortex, and small cortical abscesses. 80% of infections are secondary to E. coli (possessing P pili virulence factors). Other infecting organisms: Enterococci (Streptococcus faecalis), Klebsiella, Proteus, and Pseudomonas.
Urine culture will be positive for bacterial growth, but the bacterial count may not necessarily be be >105cfu/ml of urine Thus, if you suspect a diagnosis of acute pyelonephritis from the symptoms of fever and flank pain, but there are <105cfu/ml of urine, manage the case as acute pyelonephritis.

Investigation and treatment
- For those patients who have a fever but are not systemically unwell, outpatient management is reasonable. Culture the urine and start oral antibiotics according to your local antibiotic policy (which will be based on the likely infecting organisms and their likely antibiotic sensitivity). We use oral ciprofloxacin, 500mg bd for 10 days.
- If the patient is systemically unwell, culture urine and blood, start intravenous fluids and intravenous antibiotics, again selecting the antibiotic according to your local antibiotic policy. We use IV ampicillin 1g TDS and gentamicin 3mg/kg as a once-daily dose.
- Arrange a KUB X-ray and renal ultrasound, to see if there is an underlying upper tract abnormality (such a ureteric stone), unexplained hydronephrosis, or (rarely) gas surrounding the kidney (suggesting emphysematous pyelonephritis).
- If the patient does not respond within 3 days to this regimen of appropriate intravenous antibiotics (confirmed on sensitivities), arrange a CTU. The lack of response to treatment suggests the possibility of a pyonephrosis (i.e. pus in the kidney, which like any abscess will only respond to drainage), a perinephric abscess (which again will only respond to drainage), or emphysematous pyelonephritis. The CTU may demonstrate an obstructing ureteric calculus that may have been missed on the KUB X-ray, and ultrasound may show a perinephric abscess. A pyonephrosis should be drained by insertion of a percutaneous nephrostomy tube. A perinephric abscess should also be drained by insertion of a drain percutaneously.
- If the patient responds to IV antibiotics, change to an oral antibiotic of appropriate sensitivity when they become apyrexial, and continue this for approximately 10 - 14 days