Pyelonephritis

Pyelonephritis is an inflammation of the kidney, typically caused by a bacterial infection. It is a condition that falls under the specialties of infectious disease, urology, and nephrology. The most common causative organism is Escherichia coli. This condition requires prompt medical intervention to prevent complications such as sepsis or kidney failure.

Signs and Symptoms

The symptoms of acute pyelonephritis develop rapidly and typically include high fever, flank tenderness, and pain during urination. Patients may also experience nausea and frequent urination. In chronic cases, symptoms include persistent abdominal or flank pain, fever, unintentional weight loss, malaise, decreased appetite, and blood in the urine. Chronic pyelonephritis can lead to complications like AA amyloidosis due to the accumulation of inflammation-related proteins.

Diagram showing the typical location of pain

Causes and Risk Factors

Pyelonephritis is most commonly caused by bowel organisms that enter the urinary tract. E. coli is responsible for 70-80% of cases, followed by Enterococcus faecalis. Hospital-acquired infections may involve other bacteria like Pseudomonas aeruginosa and Klebsiella species. Risk factors include sexual intercourse, prior urinary tract infections, diabetes, structural abnormalities of the urinary tract, and spermicide use.

Diagnosis

Laboratory Examination

Diagnosis is typically based on symptoms and supported by urinalysis that shows the presence of nitrite and white blood cells. Blood tests like a complete blood count may show neutrophilia. Urine and blood cultures are useful for confirming the diagnosis and determining antibiotic sensitivity.

Imaging Studies

Imaging studies are recommended if there is no improvement with initial treatment or if kidney stones are suspected. A noncontrast helical CT scan is preferred for detecting stones, while kidney ultrasonography or voiding cystourethrography is used for identifying anatomical abnormalities.

Acute pyelonephritis with increased cortical echogenicity and blurred delineation of the upper pole

Classification

Acute Pyelonephritis

This form involves purulent inflammation of the renal pelvis and kidney. The condition reveals abscesses in the kidney parenchyma and is characterised by neutrophils, fibrin, and cell debris.

Chronic Pyelonephritis

Chronic pyelonephritis leads to recurrent infections, causing scarring and impaired kidney function. Severe cases may result in perinephric abscesses or pyonephrosis.

Chronic pyelonephritis with reduced kidney size and focal cortical thinning. Measurement of kidney length on the US image is illustrated by ‘+’ and a dashed line.

Xanthogranulomatous Pyelonephritis

This rare form is characterised by granulomatous abscess formation and significant kidney destruction. It often mimics renal cell carcinoma and is associated with recurrent fevers, anaemia, and painful kidney masses.

CD68 immunostaining on this photomicrograph shows macrophages and giant cells in a case of xanthogranulomatous pyelonephritis

Prevention

Preventive measures include urinating after sexual activity and maintaining adequate hydration. For individuals with recurrent urinary tract infections, long-term antibiotic therapy may be considered. In children, the benefits of long-term antibiotics are not conclusively proven. Cranberry products may also help reduce the incidence of UTIs in certain individuals.

Management

Antibiotics are the cornerstone of pyelonephritis treatment. In uncomplicated cases, oral fluoroquinolones like ciprofloxacin are commonly used. More severe cases may require hospital admission and intravenous antibiotics such as fluoroquinolones, aminoglycosides, or cephalosporins. Surgical intervention may be necessary for patients with structural abnormalities or stones causing urinary obstruction.

Simple

A systematic review recommended norfloxacin due to its low side effect profile and comparable efficacy. In areas with high antibiotic resistance, initial treatment may involve a single intravenous dose of a long-acting antibiotic followed by oral therapy.

Complicated

Hospitalised patients typically receive intravenous antibiotics and are monitored closely. The treatment regimen may include a combination of antibiotics based on susceptibility profiles. Intravenous fluids are administered to maintain hydration and optimise urine output.

Follow-up

If no improvement is observed within 48 hours, further urine analysis and imaging are warranted. Outpatients should check back with their healthcare provider for reassessment.

Epidemiology

Pyelonephritis affects approximately 1 to 2 per 1,000 women annually and just under 0.5 per 1,000 men. Young adult females are the most commonly affected group, followed by infants and the elderly. Xanthogranulomatous pyelonephritis is more common in middle-aged women but can present differently in children, sometimes being mistaken for Wilms' tumour.

Self-assessment MCQs (single best answer)

What is the most common causative organism of pyelonephritis?

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Which of the following is NOT a typical symptom of acute pyelonephritis?

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Which imaging study is preferred for detecting kidney stones in pyelonephritis?

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Which form of pyelonephritis involves recurrent infections leading to scarring and impaired kidney function?

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What is a common preventive measure for pyelonephritis?

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In which patient population is pyelonephritis most commonly observed?

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Which symptom is more commonly associated with chronic pyelonephritis as opposed to acute pyelonephritis?

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What is the typical antibiotic treatment used for uncomplicated pyelonephritis?

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Which of the following is a complication that can arise from chronic pyelonephritis?

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What is the recommended approach if there is no improvement in pyelonephritis symptoms within 48 hours?

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