Acute Pyelonephritis

Overview

This is an infection of the kidney parenchyma that can be organ and/or life threatening and leads to scarring of the kidney.

Complicated infection occurs in the following situations:

• Structural abnormalities of the urinary tract – vesicoureteral reflux (VUR)
• Functional abnormalities of the urinary tract
• Metabolic abnormalities predisposing one to UTIs – such as diabetes
• Unusual pathogens
• Extreme of ages – young children and elderly
• Pyeloneprhitis in men
• Recent urinary tract instrumentation
• Renal transplant due to a combination of immunosuppression and abnormal transplant kidney anatomy
• Recent antibiotic use
• Risk factors
  • Female sex
  • Obstruction
    • Allows stasis providing a medium for bacterial multiplication
    • Extrinsic causes – chronic constipation, prostatic swelling/mass (hypertrophy, infection, cancer), and retroperitoneal mass.
    • Intrinsic causes – Bladder outlet obstruction, cystocele, urinary stones, fungus ball, papillary necrosis, strictures
  • Post-menopausal state
    • Atrophic vaginal mucosa predisposes to bacterial colonization of the tract due to increased pH and absence of lactobacilli
  • Pregnancy
    • Dilation of the renal pelvis and ureters causes stasis
    • Progesterone reduces urethral peristalsis
  • Diabetes Mellitus
    • Autonomic neuropathy of the bladder – stasis
    • Glucosuria
    • Immunosuppression due to leukocyte dysfunction
    • At risk of frequent urethral catheterisation due to many hospitalisations.

Etiology

Infection may have either:

• Ascended from the lower urinary tract
• Hematogenous spread – seen in IV drug users, immunocompromised states, ureteral obstruction
• Common micro-organisms
  • Escherichia coli
  • Klebsiella pneumoniae
  • Proteus mirabilis
  • Pseudomonas aeruginosa
  • Enterococci spp
  • Staphylococci aureus
  • Staphylococcus saprophyticus
• Unusual pathogens
  • Mycobacteria
  • Candida spp
  • Opportunistic pathogens such as Corynebacterium urealyticum

Clinical Presentation

History

The classic presentation in acute pyelonephritis is the triad of:

• Fever
• Costovertebral angle pain
• Nausea and/or vomiting

Other symptoms include:

• Rigor and chills
• Malaise
• Lower urinary sx – dysuria, gross hematuria, increased frequency and urgency
• Back pain
• Suprapubic pressure/ discomfort/ pain
• Anorexia
• Young children <2years
  • Failure to thrive
  • Feeding difficulty
  • Fever
  • Vomiting
• Elderly patients
  • Fever
  • Mental status change
  • Decompensation in another organ system
  • Generalized deterioration

Physical Examination

• Vitals
  • Fever – high (can be higher than 39.4°C)
  • Pulse – tachycardia due to fever, dehydration, sepsis
  • Blood pressure – usually normal however a drop should raise suspicion of sepsis
• Costovertebral angle tenderness – most commonly unilateral over the involved kidney, although bilateral discomfort may be present
• Suprapubic tenderness

Investigations

• Urine studies – collect either clean catch sample, from urethral catheterisation, suprapubic aspiration. Urinalysis
  • Pyuria
    • 20 white blood cells (WBCs) per high-power field
  • Positive leukocyte esterase test
  • Proteinuria
  • Bacteriuria
  • Microscopic hematuria – urinary stones should be considered as a diagnosis
  • Positive nitrite – may be negative in cases with organisms that do not produce nitrate reductase.
  Urine neutrophil gelatinase-associated lipocalin
  • Sensitive biomarker for the diagnosis of acute pyelonephritis in children
  • At a cut-off value of 29.4 ng/mL, urinary NGAL had 92.5% sensitivity and 90.7% specificity for diagnosing acute pyelonephritis.
  Urine Culture
• Complete blood count
• Inflammatory markers – CRP, ESR, Procalcitonin
• Blood cultures
• Imaging studies – used in complicated cases
  • Abdominal/pelvic CT without and with contrast – contrast helps pick out urinary stones if present
  • Ultrasonography
  • MRI with diffusion-weighted imaging
  • Indications for imaging in acute pyelonephritis
    • Poorly controlled diabetes
    • Recurrent pyelonephritis
    • Anatomical or surgically corrected urinary tract anomalies
    • Hospital-acquired infections
    • Sepsis
    • Urolithiasis
    • Transplant recipients
    • Immunosuppressed individuals
    • Solitary kidneys
    • Worsening renal function
    • AIDS
    • Fever for longer than 48 hours
    • Toxicity lasting more than 72 hours
    • Unresponsive to treatment

Treatment

Uncomplicated pyelonephritis

Can be treated out-patient using:

• Antibiotics
  • Fluoroquinolone for 7 days (14 days in male patients)
  • Amoxicillin-clavulanate 875 mg orally twice daily for 7 to 10 days
  • Cefpodoxime 200 mg orally twice daily for 7 to 10 days
  • Cefadroxil 1 g orally twice daily for 7 to 10 days
  • Sulfamethoxazole-trimethoprim for 14 days
  Fluoroquinolones are the preferred antibiotic however in areas where there are high resistance patterns the other antibiotics listed can be considered.
• NSAIDS – for pain and to lower fever

Complicated pyelonephritis

Supportive therapy – IV fluids, pain management, fever management

Definitive

• Empiric antibiotics
  • An antipseudomonal carbapenem (imipenem or meropenem) plus vancomycin (for the most critically ill)
  • Ceftriaxone (usually preferred for most cases)
  • Fluoroquinolone (depending on local resistance)
  • Piperacillin-tazobactam (preferred for suspected Enterococcus or Pseudomonas)
  • Cefepime (not for ESBL)
  • Cefotaxime
  • Cefuroxime
  • Ceftazidime
  • Aztreonam
  • Aminoglycosides (gentamicin, tobramycin, or amikacin)
  • An antipseudomonal carbapenem (if a recent ESBL bacterial isolate is found)
  PLUS
  • Add vancomycin or linezolid if a Gram-positive organism is suspected.
  Intravenous antibiotics are typically given for at least 48 hours, at which point, culture results are available, and patients should have noted a positive clinical response. For patients who have responded well, consider switching to appropriate oral antibiotic treatment, as this has been shown to provide equivalent results to continued parenteral therapy. If not, consider changing antibiotics, maintaining parenteral therapy, and obtaining appropriate imaging if not already done. Consider consulting urology if imaging indicates obstruction or infectious disease if imaging is negative.

Differential Diagnoses

• Appendicitis
• Cholecystitis
• Diverticulitis
• Ectopic pregnancy
• Endometritis
• Urinary tract stones
• Ovarian cyst pathology
• Pelvic inflammatory disease
• Perinephric abscess
• Pyonephrosis (obstructive pyelonephritis)
• Renal abscess
• Rib fracture
• Costochondritis
• Lower urinary tract infection
• Chronic pyelonephritis
• Bacterial prostitis

Complications

• Emphysematous pyelonephritis
  • Necrotizing kidney infection usually caused by E. coli or Klebsiella pneumoniae.
  • Common in women and diabetic patients
  • Treated with a 3rd generation Cephalosporin + amikacin as well as surgical intervention if required
• Acute renal failure
• Chronic pyelonephritis
• Obstructive pyelonephritis
• Papillary necrosis
• Perinephric abscess
• Renal abscess
• Renal scarring and atrophy
• Renal vein thrombosis
• Sepsis and urosepsis
• Xanthogranulomatous pyelonephritis
  • Associated with chronic obstruction (from staghorn calculus [75% of cases], other calculus, stricture, or tumor)