Kidney disorders may be acute or chronic. Acute conditions usually arise suddenly, most frequently as the result of infection with inflammation of the nephrons. These diseases commonly run a course of a few weeks and are followed by complete recovery. Chronic conditions arise slowly and are often progressive, with gradual loss of kidney function.
Acute glomerulonephritis, also known as acute poststreptococcal glomerulonephritis, is the most common disease of the kidneys. This condition usually occurs in children about 1 to 4 weeks after a streptococcal throat infection. Antibodies formed in response to the streptococci attach to the glomerular membrane and cause injury. These damaged glomeruli allow protein, especially albumin, to filter into the glomerular capsule and ultimately to appear in the urine (albuminuria). They also allow red blood cells to filter into the urine (hematuria). Usually, the patient recovers without permanent kidney damage. In adult patients, the disease is more likely to become chronic, with a gradual decrease in the number of functioning nephrons, leading to chronic renal failure.
Pyelonephritis, an inflammation of the renal pelvis and the tissue of the kidney, may be either acute or chronic. In acute pyelonephritis, the inflammation results from a bacterial infection. Bacteria most commonly reach the kidney by ascending along the lining membrane from an infection in the distal part of the urinary tract. More rarely, bacteria are carried to the kidney by the blood. Acute pyelonephritis is often seen in people with partial obstruction of urine flow with stagnation (urinary stasis). It is most likely to occur in pregnant women and in men with an enlarged prostate, because the prostate surrounds the first portion of the urethra in males. Other causes of stasis include neurogenic bladder, which is bladder dysfunction resulting from neurologic lesions, as seen in diabetes mellitus, and structural defects in the area where the ureters enter the bladder. Pyelonephritis usually responds to the administration of antibiotics, fluid replacement, rest, and fever control. Chronic pyelonephritis, a more serious disease, is frequently seen in patients with urinary tract stasis or back flow. It may be caused by persistent or repeated bacterial infections. Progressive damage of kidney tissue is evidenced by high blood pressure, continual loss of protein in the urine, and dilute urine.
Hydronephrosis is the distention of the renal pelvis and calyces with accumulated fluid as a result of urinary tract obstruction. The most common causes of obstruction, in addition to pregnancy or an enlarged prostate, are a kidney stone
that has formed in the pelvis and dropped into the ureter, a tumor that presses on a ureter, and scars due to inflammation. Prompt removal of the obstruction may result in complete recovery. If the obstruction is not removed, the kidney will be permanently damaged.
A polycystic kidney is one in which many fluid-containing sacs develop in the active tissue and gradually destroy it by pressure. This disorder may run in families, and treatment has not proved very satisfactory, except for the use of dialysis machines or kidney transplantation.
Tumors of the kidneys usually grow rather slowly, but rapidly invading types are occasionally found. Blood in the urine and dull pain in the kidney region are warnings that should be heeded at once. Surgical removal of the kidney offers the best chance of cure because most renal cancers do not respond to chemotherapy or radiation.