Chronic pyelonephritis is a chronic inflammation caused by bacterial infection of the kidneys. The lesions mainly invade the renal interstitium and the renal pelvis and calyces. Due to the continuous or repeated inflammation, the renal interstitium, renal pelvis, and renal calyces are damaged, scarring is formed, and the kidneys atrophy and dysfunction occur. Usually, the patient may only have back pain and (or) low fever, but may not have obvious symptoms of urinary tract infection such as urinary pain, frequent urination, and urgency. The main manifestations are increased nocturia and a small amount of white blood cells and protein in the urine. Patients with a history of long-term or recurrent urinary tract infection may develop uremia in the late stage.