acute pyelonephritis

see also:

• urinary tract infections (UTIs) / cystitis
• renal abscesses and perinephric abscesses
• renal colic
• sepsis / septicaemia

• acute pyelonephritis is a bacterial infection of the renal parenchyma
• it usually arises from ascending bacteria in the urinary tract associated with urinary tract infections (UTIs) / cystitis
• it is 5x more likely in females as males aged under 65 years
• females have peak incidences at ages 0-4yrs, 15-35 years, then a gradual rise from age 50, peaking at 80yrs age.
• males have a peak at age 0-4 years, then gradual rise from age 35yrs to a peak at 85yrs age
• paediatric cases are often associated with underlying urologic tract abnormalities including vesicoureteral reflux
• it develops in 20-30% of pregnant women with untreated asymptomatic bacteriuria, most often during the late second and early third trimesters
• timely Rx is important to reduce renal damage, complications and also potentially lethal urosepsis

• most adult patients present with:
  • flank pain and tenderness, often with suprapubic discomfort of cystitis, developing over hours to days
  • high fever
  • anorexia, nausea +/- vomiting
• some will be afebrile
• some will have dysuria and frequency
• some will have frank haematuria associated with haemorrhagic cystitis
• elderly patients are more likely to present with delirium
• pain radiating to the groin or testis suggests renal colic
• children aged under 2yrs usually present with failure to thrive, feeding difficulty, fever, and vomiting
  • neonates may develop worsening of neonatal jaundice and may develop concurrent meningitis
• standard renal USS only has a 25-32% sensitivity for pyelonephritis (a contrast-enhanced US or CEUS is said to have over 85% sensitivity) but it is better than CT at differentiating pyonephrosis from hydronephrosis
• contrast CT abdo has sens over 85% and spec of around 88% ¹⁾
• for patients where CT is C/I, MRI has a sens of around 90%

• most require initial parenteral antibiotics for 12-48hrs, although some will be able to be managed as an outpatient with a single dose of parenteral antibiotic then a course of oral antibiotics
• iv access
• bloods for FBE, U&E
• MSU m/c/s and urinalysis
• look for and Rx evidence of sepsis / septicaemia as septic shock from urosepsis has a high mortality
• consider admission into ED observation ward if uncomplicated
• iv ceftriaxone 1g daily is a reasonable choice for most patients
• many doctors are now steering away from the use of single dose of iv gentamicin 4-5mg/kg given recent reports of permanent ototoxicity may occur with only 1 dose (although this is a rare complication)
• if highly likely to have resistant organisms (eg. ESBL) such as, PH ESBL, recent hospital admission or travel overseas (especial SE Asia where ESBL carriage is > 50%) and in septic shock:
  • IV meropenem (preferred over Tazocin in ESBL severe sepsis)²⁾ + IV amikacin (to cover carbapenem resistance), consider adding IV vancomycin if Gram +ve sepsis possible
• patients are often discharged on oral trimethoprim or cephalexin - but this depends upon your regional antibiotic resistance profiles
• patients who have returned from India are highly likely to have a multi-resistant organism which may require consultation with infectious diseases on selection of antibiotic until sensitivities are back.
• pregnant patients require inpatient care and prolonged course of antibiotics as they have ureteric stasis secondary to progesterone, etc, and have a higher risk of Rx failure
• urgent urology consult if either:
  • obstructed kidney (eg. ureteric calculus) with UTI
    • patients with renal colic and infection should be referred to urology ASAP for possible intervention to drain the urine proximal to ureteric calculus causing the obstruction
  • renal abscess
  • post-urologic procedure

• CT is generally only indicated in pyelonephritis if either:
  • there is a persistence of fever or leukocytosis after 72 hours,
  • the diagnosis is not evident from Hx,exam,urinalysis and lab results and the patient is septic and there is a need to exclude other abdominal sources of sepsis
  • there is an associated obstructing stone which is an indication for emergent nephrostomy
• non-contrast CT KUB:
  • may show gas, calculi, haemorrhage, renal enlargement, inflammatory masses, and obstruction
• contrast CT abdo:
  • may show:
    • interstitial nephritis
    • early and late stages of acute pyelonephritis
      • most characteristic finding includes one or more focal/ill-defined wedge-like regions showing reduced enhancement and poor corticomedullary differentiation, corresponding to poorly or nonfunctioning parenchyma
      • global renal swelling (88%)
      • perirenal fascial thickening (76%)
      • perinephric fat stranding (56%)
      • striated nephrogram (44%)
      • abscess (44%)
      • microabscess (32%)
      • gas in renal collecting system or parenchyma suggestive of emphysematous pyelonephritis (16%)
      • abdominal wall involvement (8%)
    • complications such as abscesses and emphysematous pyelonephritis
    • xanthogranulomatous pyelonephritis (XPN)
      • XPN is a severe form of APN that occurs mostly in middle aged women in the presence of chronic obstruction and suppuration - 80% occur in association with a staghorn calculus

• sepsis / septicaemia
• renal abscesses and perinephric abscesses which may require early surgical drainage by urology
• renal papillary necrosis
• xanthogranulomatous pyelonephritis
  • a rare (1% of all renal infections), serious, chronic inflammatory disorder of the kidney characterised by a destructive mass that invades the renal parenchyma
  • often associated with urinary tract obstruction, infection, urolithiasis / renal stones / renal calculi, diabetes mellitus, and/or immunocompromise
  • 4 x more common in women than in men
  • usually occurs in the fifth and sixth decades of life but may also occur in children under 8yrs when it is more common in boys ³⁾
• chronic pyelonephritis - usually children aged under 2yrs, associated with vesicoureteral reflux
• recurrent pyelonephritis