Pyelonephritis

Epidemiology

There is few data regarding the prevalence of pyelonephritis in children. However, the prevalence of urinary tract infections (UTIs) has been studied in multiple patient populations.

 

Prevalence of UTI by age group:

  • Preterm infants: 2.9%
  • Term infants: 0.7%
  • Preschool-age children: 1% to 3%
  • School-age children: 0.7% to 2.3%

 

Risk factors for the development of UTI:

  • Previous history of UTI
  • Siblings who have a history of UTI
  • Female sex
  • Indwelling urinary catheter
  • Intact prepuce in boys
  • Structural abnormalities of the kidneys and lower urinary tract

 

The most common and important risk factor for the development of pyelonephritis is vesicoureteral reflux (VUR), which is the abnormal flow of urine from the bladder to the upper urinary tract. VUR is either unilateral or bilateral, and is classified as grade I through V, with grade I being the least severe and grade V being the most severe.

 

reflux_0.jpg

Grades of VUG - www.urologyhealth.org/urology/articles/images/anatomy_Vesicoureteral_ref...

 

Pathophysiology

In most children outside of the neonatal period, pyelonephritis occurs after fecal flora colonize the urethra and ascend into the bladder and kidneys. However, the interval between colonization, infection and disease is unknown. E.coli O serotypes are responsible for approximately 80% of cases of pyelonephritis.

 

Presentation

The clinical manifestations of pyleonephritis are highly variable. Traditionally, pyelonephritis is suspected in any infant or child who has fever, emesis, flank pain, or costovertebral (CVA) tenderness on physical examination and a positive urine culture. Although flank pain, fever and emesis occur more often in patients with pyelonephritis than in those with lower tract disease, these findings are neither specific nor sensitive for pyelonephritis.

 

Important facts to keep in mind are:

  • Up to 25% of children who have no classic signs or symptoms of pyelonephritis are found to have upper urinary tract disease
  • 50% of children who have flank pain have no other evidence of pyelonephritis

 

In infants and toddlers:

  • Fever and irritability are the most common findings
  • Other findings include poor feeding, lethargy and abdominal pain

 

Older children:

  • May present with fever, chills, emesis, and flank pain in addition to typical signs of lower tract disease (dysuria, urgency, increased urinary frequency)
  • Clinical findings include suprapubic and CVA tenderness

 

Diagnosis

A UTI can be diagnosed when the urine culture shows:

  • Growth of greater or equal to 100,000 CFU (colony forming units)/ml of a single uropathogenic bacteria on a clean catch specimen, or 
  • Growth of greater or equal to 10,000-50,000 CFU/ml of a single uropathogenic bacteria on a clean catherization specimen.

 

However, urine cultures do not distinguish between lower and upper urinary tract infection. Although children with pyelonephritis tend to look sicker and have more fever than those with cystitis, it can be hard to distinguish these two groups.

As such, imaging studies are sometimes needed to confirm a clinical diagnosis of pyelonephritis.

 

Imaging studies:

  • Tc-99m dimercaptosuccinic acid (DMSA) renal scintography is the imaging study of choice to confirm or exclude the diagnosis of pyelonephritis
  • Computed tomography is more sensitive than ultrasonography at detecting pyelonephritis, but requires the use of IV contrast and radiation exposure

The benefit of differentiating pyelonephritis from cystitis must then be weighed against the risk of obtaining the diagnosis, and whether it will make a difference in terms of treatment.  See the section on UTI for further discussion on this topic.

 

Treatment

Children who are suspected of having pyelonephritis are started empirically on antibiotics effective against the usual pathogens for their clinical condition. Antimicrobial susceptibility testing results should then guide therapy.

IV antibiotics are administered to patients who require hospitalization. Ampicillin and gentamicin are often used empirically and parenteral antibiotics are continued until patient is afebrile for 24 hours.

Oral antibiotics (+/- one time dose of intramuscular ceftriaxone or gentamicin) are used in patients not requiring hospitalization. TMP-SMX, cephalosporins, penicillin/beta-lactamase, and ciprofloxacin (if patient is >1yo) are acceptable empiric oral agents.

Available evidence suggests that 10 to 14 days of antimicrobial therapy is adequate for uncomplicated pyelonephritis.

 

Prevention

The American Academy of Pediatrics (AAP) recommends that children younger than age 2 years diagnosed with their first UTI be evaluated with renal ultrasonography for evidence of urologic abnormalities in order to identify those patients at risk for subsequent infection and renal scarring, however these recommendations are somewhat controversial (see UTI).

Voiding cystourethrograph (VCUG) can also be performed in patients to detect vesicoureteral reflux. Currently, children with high grades (greater than grade III) of VUR are placed on long-term prophylactic antibiotics, but this too is controversial (see UTI). Those who have recurrent UTI with progressive renal damage despite prophylaxis or those with severe reflux are considered for surgical correction of the VUR.

 

Complications

Long-term complications include recurrence, renal scarring and hypertension. Because of this, early detection of pyelonephritis is critical to preservation of renal function.

 

References

  1. Chevalier, Robert. "National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC)." Vesicoureteral Reflux. National Institute of Diabetes and Digestive and Kidney Disease, 29 June 2012. Web. 25 Mar. 2013.
  2. American Academy of Pediatrics, Subcommittee on Urinary Tract Infection. Clinical Practice Guideline for the Diagnosis and Management of the Initial UTI in Febrile Infants and Children 2-24 months. Pediatrics. September, 2011, 128(3) 595-610.

  3. La Scola C, De Mutiis C, Hewitt IK, et al. Different guidelines for imaging after first UTI in febrile infants: yield, cost, and radiation. Pediatrics 2013

  4. Raszka, W. V., and O. Khan. "Pyelonephritis." Pediatrics in Review 26.10 (2005): 364-70. 
  5. Garin, Eduardo H., et al. Clinical significance of primary vesicoureteral reflux and urinary antibiotic prophylaxis after acute pyelonephritis: a multicenter, randomized, controlled study. Pediatrics 117.3 (2006): 626-632.