Overview
This lecture covers acute pyelonephritis, an upper urinary tract infection involving the kidney. It explains the definition, causes, risk factors, pathophysiology, symptoms, diagnosis, treatment, and possible complications.
Definition and Location
- Acute pyelonephritis is a rapid-onset inflammation of the renal pelvis and kidney, most often due to bacterial infection.
- The urinary tract is divided into:
- Upper tract: kidneys and ureters
- Lower tract: bladder and urethra
- Acute pyelonephritis is classified as an upper urinary tract infection.
Causes and Risk Factors
- Most cases are caused by ascending infection, where bacteria move from the urethra to the bladder, then up the ureter to the kidney.
- Risk factors shared with lower urinary tract infections include:
- Female sex
- Sexual intercourse
- Indwelling catheters
- Diabetes mellitus
- Urinary tract obstruction
- Vesicoureteral reflux (VUR) increases the risk of upper UTI by allowing urine to flow backward from the bladder to the ureter. This can result from:
- A congenital defect in the vesicoureteral orifice (the one-way valve between ureter and bladder)
- Bladder outlet obstruction, which raises bladder pressure and distorts the valve
- Obstruction also causes urinary stasis, making it easier for bacteria to colonize the urinary tract.
- Common causative bacteria for ascending infections:
- Escherichia coli (E. coli)
- Proteus species
- Enterobacter species
(All commonly found in bowel flora)
- Less commonly, infection can spread hematogenously (through the bloodstream), usually due to:
- Septicemia or bacteremia (bacteria in the blood)
- Infective endocarditis (infection of the heart’s inner layer)
- Most common organisms in this route: Staphylococcus species and E. coli
Pathophysiology and Symptoms
- Acute pyelonephritis usually affects one kidney (unilateral).
- Bacteria adhere to the renal tubule epithelium, triggering an inflammatory response.
- Chemokines attract neutrophils to the renal interstitium, but the glomeruli and blood vessels are typically spared.
- As neutrophils infiltrate and die, they pass into the urine, resulting in:
- White blood cells in urine
- White blood cell casts (WBCs and protein debris shaped like tubules)
- Blood tests may show leukocytosis (increased white blood cell count).
- Systemic symptoms, which help distinguish acute pyelonephritis from lower UTI, include:
- Fever and chills
- Nausea and vomiting
- Flank pain at the costovertebral angle
Diagnosis, Treatment, and Complications
- Diagnosis is based on clinical symptoms and findings such as white blood cells and white blood cell casts in urine.
- Treatment involves:
- Antibiotics
- Ensuring adequate hydration
- Possible complications include:
- Renal abscess formation
- Chronic pyelonephritis (especially with recurrent infections or anatomical problems)
- Papillary necrosis (death of renal papillae tissue), which can impair kidney function
Key Terms & Definitions
- Acute pyelonephritis: Sudden inflammation of the kidney, usually from bacterial infection.
- Urinary tract infection (UTI): Infection anywhere in the urinary system.
- Vesicoureteral reflux (VUR): Backward flow of urine from the bladder to the ureter.
- Leukocytosis: Increased number of white blood cells in the blood.
- White blood cell cast: Cylindrical mass of WBCs and protein from the kidney tubule, found in urine.
- Urinary stasis: Condition where urine remains stagnant, increasing infection risk.
Action Items / Next Steps
- Review and understand risk factors for urinary tract infections, especially those that increase the risk of upper UTI.
- Memorize the most common causative organisms and their typical routes of infection (ascending vs. hematogenous).
- Learn the distinguishing features and systemic symptoms of acute pyelonephritis compared to lower UTI.
- Be aware of possible complications and the importance of prompt treatment to prevent long-term kidney damage.