- Clinical science
Pyelonephritis is an infection of the renal pelvis and parenchyma that is usually associated with an ascending bacterial infection of the bladder. It occurs more commonly in females and risk factors include pregnancy and urinary tract obstruction. Patients typically present with flank pain, costovertebral angle tenderness, fever, and other features of cystitis (e.g., dysuria, frequency). Urinalysis reveals leukocyturia and bacteriuria. Urine cultures should be taken in all patients before initiating treatment to identify the pathogen and possible antibiotic resistance. Treatment depends on the drug sensitivities of the offending pathogen and the patient's clinical profile (e.g., possible comorbidities). Early empiric antibiotic treatment is essential to avoid renal complications and urosepsis.
- Usually associated with an ascending bacterial infection of the bladder ()
- Most common in women because they have shorter urethras
- Recent administration of antibiotics (possible antibiotic resistance)
- Immunosuppression (e.g., HIV, diabetes)
- Laboratory tests
Imaging: generally not necessary for diagnosis
- CT (imaging test of choice) findings include:
Ultrasound findings of the kidney and urinary bladder include:
- Urinary obstruction, calculi, or abscess
- Diffuse corticomedullary junction
- Enlarged, abnormal echogenicity, mobile during respiration (subtle changes)
- Intravenous pyelogram (IVP)
- Retrograde cystourethrogram to diagnose vesicoureteral reflux
- DMSA scan to evaluate the remaining renal function of each kidney
- Urodynamic testing to exclude neurogenic bladder or subvesical obstruction
- Destructive interstitial nephritis
- Chronic inflammatory changes such as rough scarring at the junction of the cortex and medulla
- Blunted calyces from recurrent urinary reflux
- Eosinic (not eosinophilic!) casts in the tubules (so called “thyroidization of the kidney”)
- Lipid laden foamy macrophages and multinucleated giant cells seen on histology
- Large, irregular, yellow masses appear throughout the kidney on gross examination
- Other UTIs
- See .
The differential diagnoses listed here are not exhaustive.
The choice of treatment and antibiotic therapy should be adjusted according to the Gram stain and drug sensitivities of the identified pathogen, comorbidities, and the current condition of the patient.
- Outpatient treatment
- Encourage the patient to drink adequate amounts of fluids.
- Oral treatment is often preceded by a single dose of ceftriaxone or gentamicin.
- First-line: oral (e.g., ciprofloxacin for 7 days)
- Second-line: oral trimethoprim-sulfamethoxazole for 14 days
- If there is no response within 48 hours, then check urine culture results and change treatment accordingly.
- Repeat urine culture 2–4 days after completion of the antibiotic course.
- Characterized by:
- Urinary tract abnormalities (e.g., obstruction, indwelling catheter)
- Recent surgery to the urinary tract
- Renal impairment
- Immunosuppression and/or severe comorbidities
- High-risk patient despite uncomplicated clinical picture (e.g., elderly)
- Hospitalization and adequate IV resuscitation
- First line: IV fluoroquinolones (e.g., ciprofloxacin) for 10-14 days
- Aminopenicillins + beta-lactamase-inhibitors (e.g., IV ampicillin/sulbactam); possibly in combination with an aminoglycoside
- Empiric broad-spectrum cephalosporins (e.g., IV ceftriaxone); possibly in combination with an aminoglycoside
- Carbapenem (e.g., IV meropenem or imipenem)
- Monobactam (e.g., IV aztreonam) in the event of a penicillin allergy
- Check blood cultures
- Papillary necrosis
- Emphysematous pyelonephritis
- Renal abscess
- Recurrent bacterial pyelonephritis
- Atrophic kidneys
- End-stage renal disease (ESRD): if both kidneys are affected, the patient has a single kidney, or the other kidney has been damaged by a different pathology
We list the most important complications. The selection is not exhaustive.
- The risk of pyelonephritis is increased during pregnancy
- During pregnancy, all asymptomatic cases of bacteriuria must be treated because pyelonephritis is the most common serious complication in pregnant women.
- Consequence of recurrent or persistent acute pyelonephritis
- Predisposing factors
- Clinical features
- Urinalysis: pyuria, proteinuria, WBC casts
- Imaging (ultrasound, intravenous urogram): Corticomedullary scarring (mainly upper pole), blunt/clubbed renal calyces
- Biopsy: fibrosis in the renal interstitium and eosinophilic in the renal tubules, which leads to an appearance similar to thyroid tissue (thyroidization of the kidney)
- Treat the underlying cause