Pyelonephritis

Pyelonephritis is a bacterial infection of the renal pelvis and renal parenchyma causing inflammation of the kidney. It represents the upper spectrum of urinary tract infection (UTI).


Acute Pyelonephritis

Acute suppurative bacterial infection involving:

  • Renal pelvis/Collecting system/Renal interstitium/Renal tubules

Usually occurs due to:

  • Ascending infection from lower urinary tract
  • Less commonly hematogenous spread

Chronic Pyelonephritis

Chronic tubulointerstitial inflammation and scarring due to:

  • Recurrent pyelonephritis/Vesicoureteral reflux/Chronic obstruction

Leads to:

  • Renal scarring/Tubular atrophy/CKD/Hypertension

Risk Factors

Anatomical Factors

Functional Factors

Behavioral Factors

Vesicoureteral reflux

Pregnancy

Frequent intercourse

Urinary obstruction

Diabetes mellitus

Spermicide use

Benign prostatic hyperplasia (BPH)

Immunosuppression

Poor hydration

Ureteric stone

Chronic kidney disease (CKD)


Pelviureteric junction (PUJ) obstruction

Catheterization


Neurogenic bladder

Urinary tract instrumentation


Congenital urinary tract anomalies

Urinary retention


Etiology 

Organism

Comments

Escherichia coli

Most common (~70–90%)

Klebsiella pneumoniae

Common in healthcare-associated infection

Proteus mirabilis

Associated with struvite stones

Enterococcus faecalis

Elderly/catheterized

Pseudomonas aeruginosa

Instrumentation, ICU

Staphylococcus saprophyticus

Young women

Candida albicans

Catheterized/immunocompromised

Routes of Infection

1. Ascending Infection (Most Common)

Pathogenesis:

  1. Colonization of periurethral area
  2. Ascending cystitis
  3. Vesicoureteral reflux
  4. Intrarenal reflux
  5. Renal infection

2. Hematogenous Spread

Less common.

Seen with:

  • Staphylococcus aureus bacteremia/Endocarditis
  • IV drug abuse/Immunosuppression

Classification

1. Uncomplicated Pyelonephritis

Occurs in:

  • Healthy nonpregnant women
  • Normal urinary tract

2. Complicated Pyelonephritis

Associated with:

  • Structural abnormality
  • Obstruction
  • Catheter
  • Stone
  • Diabetes
  • Male sex
  • Pregnancy
  • CKD
  • Immunosuppression

Higher risk of:

  • MDR organisms
  • Abscess
  • Septic shock

3. Emphysematous Pyelonephritis

Necrotizing gas-forming renal infection.

Common in:

  • Diabetes mellitus

Common organisms:

  • Escherichia coli
  • Klebsiella pneumoniae

High mortality.


4. Xanthogranulomatous Pyelonephritis

Chronic destructive granulomatous renal infection.

Associated with:

  • Staghorn calculi
  • Chronic obstruction

Usually caused by:

  • Proteus mirabilis
  • Escherichia coli

Clinical Features

Classic Triad

  1. Fever
  2. Flank pain
  3. Nausea/vomiting

Symptoms

Symptom

Mechanism

Fever with chills

Systemic inflammation

Flank pain

Renal capsule distension

Dysuria

Associated cystitis

Frequency

Lower UTI

Urgency

Bladder irritation

Nausea/vomiting

Cytokine response

Malaise

Systemic illness

Hematuria

Mucosal inflammation

Physical Examination

Finding

Significance

Fever

Infection

Tachycardia

Sepsis

Hypotension

Septic shock

CVA tenderness

Renal inflammation

Suprapubic tenderness

Cystitis

Delirium

Elderly sepsis

Special Presentations

Elderly

May present with:

  • Delirium
  • Weakness
  • Falls
  • Sepsis without urinary symptoms

Pregnancy

Risk:

  • Preterm labor
  • ARDS
  • Sepsis

Usually due to:

  • Progesterone-mediated ureteric dilation
  • Urinary stasis

Diabetics

Higher risk of:

  • Emphysematous pyelonephritis
  • Papillary necrosis
  • Renal abscess

Diagnosis

Urinalysis

Finding

Significance

Pyuria

Hallmark

Leukocyte esterase

WBCs

Nitrite positive

Gram-negative bacteria

WBC casts

Suggest upper UTI

Mild proteinuria

Tubular inflammation

Hematuria

Inflammation

Urine Culture

Gold standard.

Significant bacteriuria:

  • Usually ≥10^5 CFU/mL
  • Symptomatic patients may have lower counts

Blood Tests

Investigation

Findings

CBC

Leukocytosis

CRP/ESR

Elevated

Procalcitonin

May correlate with severity

Renal function

AKI

Electrolytes

Sepsis-associated changes

Lactate

Severe sepsis

Blood Cultures

Positive in:15–30%

Indications:Sepsis/ICU/Immunocompromised/Severe pyelonephritis


Imaging

Ultrasound

Useful for:Hydronephrosis/Obstruction/Abscess/Stones


CT Abdomen/Pelvis (Best Imaging)

Contrast CT shows:

  • Wedge-shaped hypodensities
  • Renal enlargement
  • Perinephric stranding
  • Abscess
  • Gas formation

Indications:

  • Severe illness
  • Persistent fever >48–72 h
  • Suspected obstruction
  • AKI
  • Diabetes
  • Immunocompromised
  • Recurrent pyelonephritis

MRI

Alternative when:

  • Pregnancy/Contrast contraindicated

Differential Diagnosis

Condition

Distinguishing Features

Renal colic

Colicky pain, no fever

Appendicitis

RLQ pain

Cholecystitis

RUQ pain

PID

Pelvic findings

Renal abscess

Persistent fever

Perinephric abscess

Toxic appearance

Glomerulonephritis

RBC casts

Lower UTI

No flank pain/fever

Complications

Local Complications

Complication

Description

Renal abscess

Localized pus collection

Perinephric abscess

Extension outside kidney

Papillary necrosis

Seen in diabetes

Emphysematous pyelonephritis

Gas-forming infection

Pyonephrosis

Infected obstructed kidney

Systemic Complications

Complication

Description

Sepsis

Systemic inflammatory response

Septic shock

Vasopressor-requiring hypotension

AKI

Sepsis + tubular injury

ARDS

Severe inflammatory response

DIC

Severe sepsis

Management

Antibiotic Therapy

Uncomplicated Pyelonephritis (Outpatient)

Oral Options

Drug

Typical Regimen

Ciprofloxacin

500 mg BD

Levofloxacin

750 mg OD

TMP-SMX

If susceptible

Oral beta-lactams

Less effective

Duration:

  • 5–14 days depending on agent

Hospitalized Patients

IV Antibiotics

Antibiotic

Uses

Ceftriaxone

Common empiric therapy

Piperacillin-tazobactam

Complicated infection

Cefepime

Hospital-acquired infection

Carbapenem

ESBL organisms

Aminoglycosides

Severe gram-negative infection

ICU/Septic Shock

Empiric therapy should cover:

  • ESBL organisms
  • Pseudomonas aeruginosa if risk factors
  • Resistant gram-negatives

Examples:

  • Meropenem
  • Piperacillin-tazobactam + amikacin
  • Cefepime + aminoglycoside

Pregnancy

Preferred:

  • Ceftriaxone
  • Cefepime
  • Amoxicillin-clavulanate

Avoid:

  • Fluoroquinolones
  • Tetracyclines

Catheter-Associated Pyelonephritis

Management:

  • Remove/replace catheter
  • Culture-directed therapy
  • Assess for obstruction

Duration of Therapy

Situation

Duration

Uncomplicated

5–7 days (fluoroquinolone)

Complicated

10–14 days

Abscess

2–4 weeks

Bacteremia

Usually 10–14 days

Source Control

Urgent Urological Intervention Needed In:

  • Obstructive pyelonephritis
  • Pyonephrosis
  • Infected stone
  • Hydronephrosis with sepsis

Methods:

  • Percutaneous nephrostomy
  • Ureteric stenting

This is a urological emergency.