(See also Overview of Kidney Filtering Disorders.)
Tubulointerstitial nephritis is inflammation that affects the tubules of the kidneys and the tissues that surround them (interstitial tissue).
This disorder may be caused by diseases, drugs, and toxins that damage the kidneys.
People may have excessive urination, urinate at night, or have fever and/or a rash.
Laboratory tests of blood and urine are done as well as usually imaging tests and sometimes a kidney biopsy.
Stopping exposure to harmful drugs and toxins and treating underlying disorders improve kidney function.
Tubulointerstitial nephritis may be
Tubulointerstitial nephritis often results in kidney failure (loss of most kidney function). It may be caused by various diseases, drugs, toxins, or radiation that damages the kidneys. Damage to the tubules results in changes in the amounts of electrolytes (for example, sodium and potassium) in the blood or in problems with the kidney's ability to concentrate urine, resulting in urine that is too dilute. Problems concentrating urine causes an increase in daily urine volume (polyuria) and difficulty maintaining the proper balance of water and electrolytes in the blood.
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 usually from 3 days to 5 weeks.
Drugs can also cause tubulointerstitial nephritis through nonallergic mechanisms. For example, NSAIDs can directly damage the kidney, taking up to 18 months to cause chronic tubulointerstitial nephritis.
Infection of the kidneys (pyelonephritis) can also cause acute or chronic tubulointerstitial nephritis. Kidney failure is unlikely unless inflammation causes a blockage in the urinary tract or pyelonephritis occurs in both kidneys.
Some people have few or no symptoms. When symptoms develop, they are highly variable and may develop suddenly or gradually.
When tubulointerstitial nephritis develops suddenly, the amount of urine produced may be normal or less than normal. Sometimes the amount of urine produced is excessive and people urinate more frequently and waken during the night to urinate (nocturia). If the cause is pyelonephritis, symptoms may include fever, painful urination, and pain in the lower back or side (flank). If the cause is an allergic reaction, symptoms may include 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. The amount of urine produced may be greater than normal.
Laboratory tests (kidney function tests) usually detect signs of kidney failure, such as an increase in the level of waste products in the blood, or other characteristic abnormalities, such as metabolic acidosis and low levels of potassium, uric acid, or phosphate. A kidney biopsy is the only conclusive means of diagnosing tubulointerstitial nephritis, although a biopsy is rarely done 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 do not normally appear in the urine, but when they do, a person may have acute tubulointerstitial nephritis caused by an allergic reaction. In such cases, blood tests may show that the number of eosinophils in the blood is 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 radionuclide scanning or ultrasonography, which are imaging studies done to differentiate acute tubulointerstitial nephritis from other sudden kidney disorders.
Kidney function usually improves when an offending drug is stopped or treatment of the underlying disorder is effective, although some kidney scarring is common. The prognosis tends to be worse when the offending drug is an NSAID.
When the inflammation occurs gradually, kidney damage may develop at different rates in different portions of the kidney. The person may develop abnormalities characteristic of damage to different portions of the kidney at different times. However, kidney damage usually progresses to involve most or all of both kidneys and becomes irreversible.
The first step in treating acute tubulointerstitial nephritis is to stop whatever drug is causing the kidney damage and treat the underlying disorder. Treatment with a corticosteroid may speed the recovery of kidney function when tubulointerstitial nephritis is caused by certain disorders (such as systemic lupus erythematosus and Sjögren syndrome) or 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.
Chronic tubulointerstitial nephritis is treated by stopping the causative drug or treating the underlying disorder. Supportive care such as controlling blood pressure is often used. Drugs may be used to try to slow progression of kidney disease. Irreversible severe kidney damage, whatever the cause, results in the need for dialysis or kidney transplantation.