SUPERStudy: Pyelonephritis

By usmlevideoss

Introduction

Pyelonephritis is a bacterial infection of the kidney parenchyma and renal pelvis, often originating from an ascending urinary tract infection (UTI). It is classified into:

  • Acute pyelonephritis: Severe, symptomatic infection.
  • Chronic pyelonephritis: Associated with long-term complications such as renal scarring.

Etiology

  1. Primary Pathogens:
    • Gram-negative bacteria are the most common culprits, including:
      • Escherichia coli (E. coli) (most common)
      • Proteus, Klebsiella, Enterobacter, and Pseudomonas.
  2. Predisposing Factors:
    • Vesicoureteral reflux
    • Urinary obstruction (e.g., stones, strictures)
    • Diabetes mellitus
    • Immunosuppression
    • Catheterization

Epidemiology

  • Demographics:
    • More common in women due to shorter urethra and proximity to the anus.
  • Incidence:
    • Peaks in sexually active women aged 15–35 years.
  • Risk Factors:
    • Pregnancy, diabetes, anatomical abnormalities, prior UTI history.
    • Acute pyelonephritis: Most common serious nonobstetrical medical complication during pregnancy.

Pathophysiology

  • Bacteria ascend from the bladder to the kidneys via the ureters.
  • Infection triggers an inflammatory response in the renal parenchyma, resulting in:
    • Tissue damage and edema.
    • Severe cases: Abscess formation or scarring.
    • Chronic cases: Renal atrophy and dysfunction.

Clinical Manifestations

  1. Symptoms:
    • Fever, shaking chills, flank pain.
    • Dysuria, urgency, frequency.
    • Associated: Nausea, vomiting, and diarrhea.
  2. Signs:
    • Fever, tachycardia.
    • Costovertebral angle tenderness (CVA).
    • Severe cases: Sepsis, hypotension

Diagnosis

  1. History and Physical Examination:
    • Hallmark triad: Fever, flank pain, urinary symptoms.
  2. Urinalysis:
    • Pyuria, bacteriuria, leukocyte casts, hematuria.
  3. Urine Culture:
    • Identifies the causative organism.
  4. Imaging (in severe or recurrent cases):
    • CT scan or ultrasound to detect abscess or obstruction.

Treatment

  1. Supportive Measures:
    • Intravenous hydration: Ensures adequate urinary output.
  2. Antibiotic Therapy:
    • Empirical antibiotics: Broad-spectrum, including:
      • Ampicillin + gentamicin, ampicillin/sulbactam.
      • Cefazolin, ceftriaxone, mezlocillin, piperacillin.
    • Adjust regimen based on culture sensitivity.
    • Severe cases: Require hospitalization, IV antibiotics, and supportive care.
  3. Address Predisposing Factors:
    • Treat underlying issues such as urinary obstruction or stones.
  4. In Pregnancy:
    • Prevent acute pyelonephritis by screening for and treating asymptomatic bacteriuria.

SUPERPoint

The hallmark of acute pyelonephritis is fever, flank pain, and costovertebral angle tenderness with evidence of urinary infection (e.g., pyuria, bacteriuria).

SUPERFormula

Patient reports fever, flank pain, dysuria + Costovertebral angle tenderness + Bacterial infection ascending from the lower urinary tract + Commonly caused by Escherichia coli or other uropathogens + Risk factors: female gender, pregnancy, diabetes, urinary obstruction + Inflammatory response in renal parenchyma and pelvis + Diagnosis via urinalysis, urine culture, and imaging (if needed) = Acute Pyelonephritis.

References: 

-25-03: Genitourinary Tract Infections 

Mathew Sorensen; Marah C. Hehemann; Maahum A. Haider; Current Medical Diagnosis & Treatment 2025

-CURRENT Diagnosis & Treatment: Obstetrics & Gynecology, 12e > Renal & Urinary Tract Disorders in Pregnancy

Alan H. DeCherney, Lauren Nathan, Neri Laufer, Ashley S. Roman

-CHAPTER 56: Renal and Urinary Tract Disorders; Williams Obstetrics, 26e