Section 11. Kidney and Urinary Tract Disorders

Chapter 144. Nephritis

Topics: Introduction | Nephritic Syndrome | Nephrotic Syndrome | Asymptomatic Proteinuria and Hematuria Syndrome | Tubulointerstitial Nephritis

Tubulointerstitial Nephritis

Tubulointerstitial nephritis is inflammation that affects the tubules of the kidneys and the tissues that surround them (tubulointerstitial tissue).

Tubulointerstitial nephritis may be acute or chronic, and it often results in kidney failure. It may be caused by various diseases, drugs, or toxins that damage the kidneys.

Causes

The most common cause of acute tubulointerstitial nephritis is an allergic reaction to a drug. Antibiotics such as penicillin and the sulfonamides, diuretics, and nonsteroidal anti-inflammatory drugs (NSAIDs)--including aspirin--may trigger an allergic reaction. The interval between the exposure to the allergen that caused the reaction and the development of acute tubulointerstitial nephritis varies from 5 days to 5 weeks.

Bacterial infection of the kidneys (pyelonephritis) can also cause acute or chronic tubulointerstitial nephritis.

Symptoms and Diagnosis

Some people have few or no symptoms. When symptoms develop, they are highly variable, and they may develop suddenly or gradually.

When tubulointerstitial nephritis develops suddenly, the amount of urine produced may be normal or less than normal. Some people develop the symptoms of a urinary tract infection: fever, painful urination, pus in the urine, and pain in the lower back or side (flank). If the cause is an allergic reaction, symptoms may include a fever and a rash.

When tubulointerstitial nephritis develops gradually, the first symptoms to appear are those of kidney failure, such as itchiness, fatigue, decreased appetite, nausea, vomiting, and difficulty breathing. Blood pressure is normal or only slightly above normal in the early stages of the disease.

Laboratory tests usually detect signs of kidney failure, such as an increase in the level of waste products in the blood. A kidney biopsy is the only conclusive means of diagnosing this disorder, although a biopsy is rarely performed except when the cause cannot be found or treatment with corticosteroids is being considered.

When tubulointerstitial nephritis develops suddenly, the urine may be almost normal, with only a trace of protein or pus, but often the abnormalities are striking. The urine may show large numbers of white blood cells, including eosinophils. Eosinophils rarely appear in the urine, but when they do, a person almost certainly has acute tubulointerstitial nephritis caused by an allergic reaction. Also, the number of eosinophils in the blood may be increased.

When an allergic reaction is the cause, the kidneys usually are large because of inflammation caused by the allergic reaction. This enlargement can be seen with x-rays or ultrasound scanning.

Prognosis and Treatment

Kidney function usually improves when an offending drug is discontinued or treatment of the underlying disease is effective, although some kidney scarring is common. Treatment with a corticosteroid may speed the recovery of kidney function when the disorder is caused by an allergic reaction. If kidney function worsens and kidney failure develops, dialysis is usually needed. In some cases, the damage is irreversible, and kidney failure becomes chronic.

When the inflammation occurs gradually, kidney damage may develop at different rates in different portions of the kidney. When the proximal tubule is damaged, the normal reabsorption of sodium, potassium, bicarbonate, uric acid, and phosphate may be altered, resulting in low bicarbonate (metabolic acidosis), low potassium (hypokalemia), low uric acid (hypouricemia), and low phosphate (hypophosphatemia). Injuries to the distal tubule are usually associated with a loss of urine concentrating ability and an increase in daily urine volume (polyuria). Kidney damage usually progresses to involve most or all of the kidney, resulting in the need for dialysis or kidney transplantation.