Urinary tract infections are a severe public health problem caused by a range of different pathogens. When infection migrates to the upper urinary tract, or is seeded there via blood, both the pelvis and parenchyma of the kidney become inflamed. This condition is then characterized as pyelonephritis.
Pyelonephritis is characteristic for all age-groups, but with recognized peak ages in infancy (particularly in girls), the childbearing years for women and the elderly (especially in men with prostate pathology). The risk factors in these groups are relatively short urethra in infant girls, urinary tract obstruction by the enlarging uterus during pregnancy, and the chronic obstruction as a result of prostatic hyperplasia.
The clinical manifestations of pyelonephritis can be highly variable. Classic symptoms of pyelonephritis include a sudden onset of chills, fever (body temperature of 38 °C or greater), and unilateral or bilateral flank pain with costovertebral tenderness. These signs are usually accompanied by dysuria, urinary frequency and urgency.
It is important to stress out that none of these symptoms is reliable for determining the anatomic level of infection. In addition, gastrointestinal symptoms can be also present in acute pyelonephritis – namely abdominal pain, diarrhea, nausea and vomiting. All the aforementioned signs can confound the diagnosis.
Children younger than two years of age may only present with a high fever without symptoms related to the urinary tract. Other findings include poor feeding, abdominal pain and lethargy. Older children can present with fever, chills, emesis and flank pain, including the typical signs such as dysuria and urgency.
Furthermore, one third of frail, elderly patients with acute pyelonephritis have no fever, and may not exhibit other classic manifestations of the disease. In 20 percent of elderly patients, the predominant symptoms are pulmonary or gastrointestinal.
In contrast to acute pyelonephritis, chronic pyelonephritis represents a progressive process. It most frequently presents insidiously as progressive renal failure, often with hypertension. Approximately 11% to 20% of end-stage renal disease is a result of chronic pyelonephritis.
Establishing a diagnosis
Medical history and adequate physical examination represent the most helpful tools for establishing a diagnosis of acute pyelonephritis. Still, to confirm the diagnosis, laboratory tests such as urinalysis and urine culture are employed. Urine specimens are obtained by a midstream clean-catch technique, which is a standard practice for obtaining a useful specimen.
Laboratory findings include pyuria, bacteriuria, granular or leukocytic casts, and a positive urine culture. Hematuria may be present in individuals with cystitis and pyelonephritis. Blood tests may show elevated erythrocyte sedimentation rate, elevated CRP levels and leukocytosis with a neutrophilic shift.
Positive blood cultures that grow the same organism as cultured from the urine are sometimes found, most often in hospitalized patients. Still, there is no evidence that this finding indicates a more complicated course of the disease in otherwise healthy persons with pyelonephritis.
Imaging studies are sometimes required to confirm a clinical diagnosis of pyelonephritis. Ultrasound can easily detect the presence of obstruction, as well as demonstrate characteristic findings suggestive of acute pyelonephritis. Computed tomography is more sensitive than ultrasonography at spotting the condition, but requires the use of intravenous contrast and radiation exposure.
Other disorders that may arise from or mimic acute pyelonephritis should be considered. The differential diagnosis of this condition includes cholecystitis, appendicitis, pelvic inflammatory disease, lower lobe pneumonia, perforated viscus and the prodrome of herpes zoster. Chronic pyelonephritis also has non-specific morphology and can be the result of numerous diverse etiologic factors.