Pyelonephritis is an infectious disease that involves both the parenchyma and the pelvis of the kidney. It may occur acutely or chronically and with or without urinary obstruction.

Acute pyelonephritis is a purulent inflammatory bascterial infection, usually affecting one kidney. Women are more commonly affected than men, and in children pyelonephritis is responsible for 2-5% of all illnesses.

The typical symptoms are flank pain accompanied by fever, shaking chills and severe general malaise. At the same time cystitis can occur with frequent, severe urgency and pain on urination. Percussion over the affected kidney is painful and the urinalysis shows leukocyturia and bacteriuria. Primarily the infection ascends from the bladder via the ureters or lymphatic vessels to the kidney. Spread of the infection through the blood vessels is uncommon and occurs from other purulent sites or tuberculosis.

Obstruction of the upper urinary tract (ureter, surrounding tissue) or the lower urinary tract (bladder, prostate, urethra) can increase susceptibility to pyelonephritis. Obstructed urinary flow can be caused by stones, malformations, as well as infections, tumors or scar forming diseases. In children pyelonephritis is often due to reflux of infected urine from the bladder to the kidney (vesicoureteral reflux).

Acute infections are treated with antibiotics for two weeks. If the patient does not respond to treatment within 24-48 hours, an obstruction of the urinary tract or an abscess of the kidney or its capsule must be considered. If an obstruction is identified the first line of treatment is the emergency drainage of the kidney accompanied by antibiotic therapy. Incorrect or inadequate treatment of pyelonephritis can have serious consequences, such as chronic infection, septicemia and death.

Chronic pyelonephritis is a chronic infection of the kidney, where a persistent bacterial infection may not be present or detectable. Chronic pyelonephritis leads to scarring and shrinkage of the renal parenchyma and increasing loss of function until in the final stage an atrophic non-functional kidney remains.

Vesicoureteral reflux frequently leads to chronic kidney infections during the first years of life. In adults diabetes, calculi, analgesic nephropathy or obstructive uropathy increase susceptibility to chronic infections. Unspecific symptoms such as general malaise, back pain, weight loss and gastrointestinal complaints predominate. Other serious late consequences are renal insufficiency and hypertension.

The clinical examination is often of little help. 30% of patients have anemia and hypertension. Urinalysis shows proteinuria, leukocyturia and bacteriuria. The excretory urogram is abnormal with inflammatory changes.

The best therapy for chronic pyelonephritis is its prevention by adequate therapy of acute urinary tract infections and correction of obstructive uropathy or reflux as well as risk factors. Children need a long-term pathogen-specific antibiotic treatment, especially in the presence of vesicoureteral reflux.