Introduction:
Urinary tract infection is the most common infection in children. Acute pyelonephritis (inflammation of the kidney due to bacterial infection) in children may lead to renal scarring, which later increases the risk of hypertension, preeclampsia (a pregnancy condition with hypertension), proteinuria (presence of protein in urine), and renal insufficiency. Vesicoureteral reflux (reverse flow of urine) is considered the most common cause of renal scar formation in children. In addition, excess scarring may further progress renal injury.
What Is Meant by Urinary Tract Infection?
Urinary tract infection is defined as the presence of pure bacterial growth of a single species that contains more than one lakh colony-forming units per milliliter of urine. Recurrent urinary tract infection is defined as more episodes of urinary tract infection with cystitis (inflammation of the kidneys) and lower urinary tract infection. In a male infant, an attack of urinary tract infection and its recurrence signals urogenital evaluation for congenital abnormalities.
What Are the Causes of Renal Scarring?
-
Acute pyelonephritis (inflammation of the kidney due to bacterial infection) in children may lead to renal scarring, which results from a complex interaction between host and bacterial factors, leading to acute renal parenchymal damage and subsequent permanent damage.
-
Extensive scarring may progress to further renal injury with subsequent hypertension, decreased renal function, proteinuria, and sometimes end-stage renal disease.
-
Glomerulonephritis - Scarring of tiny blood vessels in the kidney.
-
Physical injury.
-
Swelling.
-
Lack of blood circulation to the kidney.
-
Abnormal allergic or immune reactions.
-
Diabetes.
-
Drugs.
-
Lupus erythematosus (autoimmune disease).
What Are the Risk Factors for Renal Scar Formation?
-
Age.
-
Gender.
-
Recurrent infection.
-
Peak fever.
-
Treatment delay.
-
Presence of vesicoureteral reflux (reverse flow of urine).
-
Laboratory indices of inflammation such as total white blood cell count, erythrocyte sedimentation rate, and C-reactive protein level.
-
Bacterial virulence.
-
Host defense factors.
-
Genetic susceptibility.
What Are the Symptoms of Renal Scarring?
-
Excess protein in the urine.
-
Swollen ankles.
-
Build up of fluid in the abdomen.
-
Blood in the urine.
What Is the Pathogenesis of Renal Scar Formation in Urinary Tract Infections?
-
The exact pathogenesis of renal scarring is not well understood.
-
According to Roberts, the acute inflammatory response meant to eradicate the invading bacteria is also responsible for early renal parenchymal damage and subsequent scarring.
-
This process is an inflammatory response that features chemotaxis, phagocytosis, the release of lysosomal enzymes and superoxide, the production of peroxide and hydroxyl radicals, tubular ischemia, and reperfusion injury. The fibrosis that follows is initiated mainly by macrophages.
-
The pathogenesis of proteinuria in reflux nephropathy is also not well understood, and it is variably attributed to immunological injury, macromolecular trapping and mesangial dysfunction, vascular alterations and hypertension, and glomerular hyperfiltration.
-
Hypertension occurs in ten percent to 30 % of children and young adults with renal scarring, and it may take up to eight years to develop.
-
The exact cause of hypertension due to renal scarring is unknown but may be due to segmental ischemia (death of tissue) with increased renin secretion, and it is not dependent on scarring severity.
What Is the Pathogenesis of Renal Scar Formation in Glomerulonephritis?
-
The blood in the kidneys is filtered with the help of glomeruli and also helps in the removal of waste fluids from the kidneys.
-
Once the glomeruli are damaged, it does not filter the blood and results in leakage of protein urine.
-
This causes scarring of tiny blood vessels in the glomeruli.
Who Is at High Risk for Renal Scarring?
-
High-risk children include those with an increased level of procalcitonin, which has high sensitivity in identifying children with severe reflux.
-
Those with a high fever who are younger than six months of age, recurrent urinary tract infection, clinical signs such as a poor urinary stream or palpable kidneys, infection with atypical organisms, bacteremia or septicemia, prolonged clinical course with failure to respond fully to antibiotic treatment within 48 to 72 hours.
-
Unusual clinical presentations such as an older boy or with a known abnormality on antenatal ultrasound screening of the urinary tract.
-
Such high-risk children should undergo ultrasonography with their first episode of urinary tract infection.
How to Diagnose Renal Scarring?
-
Renal Biopsy- This procedure involves taking a tiny piece of tissue from the kidney and sending it to the lab, where a pathologist examines the tissue samples under a microscope for any signs of disease. It is done in cases of infection, kidney inflammation, scarring, and unusual deposits of a protein called immunoglobulin.
-
Glomerular Filtration Rate- A glomerular filtration rate blood test helps to check kidney function. The kidneys have tiny filters called glomeruli which help to remove waste and excess fluid from the blood. A glomerular filtration test estimates the quantity of blood passing through these filters each minute.
-
Kidney Ultrasound- Ultrasound helps to detect blockages in the blood vessels.
-
Genetic Testing- Genetic testing looks for changes, sometimes called mutations or variants in DNA.
How to Treat Renal Scarring?
There is no appropriate treatment for renal scarring. The treatment can be given for symptomatic relief.
-
Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers- reduces blood pressure that helps control protein loss.
-
Steroids such as Prednisolone and other immune system-suppressing drugs help to reduce protein loss and improve kidney function.
-
Statins are used to control cholesterol.
-
Anticoagulants are used to prevent blood clots.
-
Diuretics help to remove excess salt from the body, thereby reducing swelling.
-
If the renal scarring is due to glomerulonephritis, then dialysis and renal transplant are the proposed choice of treatment.
-
Along with that, one should regularly monitor the kidneys with blood and urine tests.
-
Antiinflammatory or antioxidant therapy given concomitantly with antibiotics lowers the risk of post-pyelonephritic scarring.
How to Prevent Renal Scarring?
Antioxidant therapy with vitamin A or E when given to children with pyelonephritis, may lower the risk of renal scarring.
Conclusion:
In spite of recognizing the cause of renal scarring previously attributed to infection, the prevention of renal scarring remains the goal of all therapies for childhood urinary tract infections. Hence, children at high risk of renal scar formation after urinary tract infection should be evaluated and treated.
