What is calculous pyelonephritis

Calculous Pyelonephritis: Diagnosis and Management

Calculous pyelonephritis is a severe bacterial infection of the kidney and renal pelvis that occurs in the presence of urinary tract obstruction caused by kidney or ureteral stones, requiring urgent intervention to prevent progression to urosepsis and permanent renal damage. 1, 2

Clinical Presentation

• Typical symptoms:

  • Fever (>38°C)
  • Chills
  • Flank pain or costovertebral angle tenderness
  • Nausea and vomiting
  • Lower urinary tract symptoms (urgency, dysuria, frequency)
  • In severe cases: signs of sepsis or septic shock 3

• Risk factors:

  • Urinary tract obstruction (most commonly stones)
  • Diabetes mellitus
  • Immunocompromised status
  • Anatomical anomalies of the urinary tract
  • Vesicoureteral reflux 4

Diagnostic Approach

1. Laboratory evaluation:

   • Urinalysis: pyuria and bacteriuria
   • Urine culture with antimicrobial susceptibility testing (essential in all cases)
   • Blood cultures (in complicated cases or suspected sepsis)
   • Serum inflammatory markers (in complicated cases) 3, 5

2. Imaging studies:

   • Ultrasound: First-line imaging to detect hydronephrosis and possible pus presence
   • CT with contrast: Most sensitive for confirming diagnosis and determining the cause of obstruction
     • Findings may include: parenchymal changes, hydronephrosis, perinephric stranding, and visualization of the obstructing stone
     • Should be performed if patient fails to respond to 72 hours of appropriate antibiotic therapy 3, 4

Management

1. Urgent decompression of the collecting system in obstructive calculous pyelonephritis:

   • Percutaneous nephrostomy OR
   • Ureteral stent placement 4

2. Antimicrobial therapy:

   • Outpatient (uncomplicated cases):

     • Oral fluoroquinolones or trimethoprim/sulfamethoxazole
     • When local resistance exceeds 10%, add one dose of a long-acting broad-spectrum parenteral antibiotic while awaiting susceptibility results 5

   • Inpatient (complicated cases):

     • Initial intravenous antimicrobial regimen: fluoroquinolone, aminoglycoside (with or without ampicillin), or extended-spectrum cephalosporin/penicillin
     • Carbapenems should be reserved for patients with multidrug-resistant organisms 3
     • Duration: 5-14 days depending on clinical response and antimicrobial agent 4

3. Definitive treatment of the stone:

   • After resolution of acute infection
   • Options include extracorporeal shock wave lithotripsy, ureteroscopy with stone extraction, or percutaneous nephrolithotomy 1

Monitoring and Follow-up

• Most patients respond to appropriate management within 48-72 hours
• If no improvement occurs within this timeframe:
  • Repeat imaging (CT with contrast)
  • Repeat cultures
  • Consider alternative diagnoses 3, 5

Complications

• Permanent renal damage and scarring
• Renal or perirenal abscess formation
• Emphysematous pyelonephritis (gas-forming infection, particularly in diabetic patients)
• Pyonephrosis (pus accumulation in obstructed collecting system)
• Sepsis and septic shock
• Chronic renal failure 4, 6

Special Considerations

• Pregnancy: Pregnant patients with pyelonephritis have significantly elevated risk of severe complications and should be admitted for initial parenteral therapy 5
• Diabetes: Higher risk of complications including emphysematous pyelonephritis; may present with atypical symptoms 4, 6

Calculous pyelonephritis represents a urological emergency requiring prompt diagnosis and treatment to prevent significant morbidity and mortality. The combination of appropriate antimicrobial therapy and urgent relief of obstruction forms the cornerstone of management.