An Overview of Acute Interstitial Nephritis

Interstitial nephritis is a disease entity characterized by an inflammatory process involving the kidneys' tissue, which can lead to a decline in kidney function and even complete kidney failure. A simple way of looking at interstitial nephritis is to think of it as an allergic reaction localized to the kidney (although that is an over-simplification).

Signs and Symptoms

Interstitial nephritis is typically divided into two categories depending on the rate of onset, and the rapidity of decline of kidney function. These two categories are:

1. Acute interstitial nephritis (AIN), which is typically a sudden, and usually shorter lasting decline in kidney function.
2. Chronic interstitial nephritis (CIN) which is a much more of a chronic, long term disease process.

Typically symptoms and signs, which tend to be more impressive with acute interstitial nephritis, include:

• Fever
• Skin rash
• Pain in the flanks
• Elevated counts of a particular kind of white blood cell (called eosinophils)
• Elevated blood level of creatinine, a marker whose level is commonly tested to assess your kidney function
• Presence of elevated eosinophils in the urine
• Presence of red blood cells in the urine (the amount could be small enough for you to not be able to appreciate it with the naked eye)
• Increase protein spillage into the urine. This is referred to as "proteinuria," and considered a non-specific finding of kidney damage.

Although the above-mentioned symptoms and signs are considered "classic textbook symptoms," they might not always be seen in all patients.

Causes

As described above, interstitial nephritis is almost like having an inflammatory or allergic reaction in the kidney, and is usually set off by certain inciting factors. The agent provocateur behaves like an "allergen" which sets off the allergic reaction. Drugs are a common reason, but other entities are possible as well. Here is an overview of some common culprits:

• Medications: These include antibiotics like penicillins, quinolones (eg. ciprofloxacin), common over-the-counter pain medications like NSAIDs, acid reflux medications (referred to as proton pump inhibitors), water pills/diuretics, etc. Why someone would react to a particular medication, while others do perfectly fine, is not fully understood, but is related to the way our immune system's response to a particular inciting factor. This is just like how everyone is not necessarily susceptible to allergy from peanuts, for instance.
• Infections: Infections are known to cause interstitial nephritis. Theoretically, any infectious agent could be an inciting factor, but, examples include bacteria like streptococci, viruses like Epstein-Barr virus, leptospira, and parasites.
• Autoimmune diseases: Another common entity known to be associated with acute interstitial nephritis. These include well-known autoimmune diseases like lupus, or systemic lupus erythematosus (SLE), Sjogren's syndrome, etc.
• TINU (tubulointerstitial nephritis with uveitis) syndrome - This is a specific entity whose pathogenesis is not known. Medications, infectious agents like chlamydia, and a certain Chinese herb by the name of "Goreisan", have all been considered potential suspects. The affected patient will report flank pain, blood, or protein in the urine, and will be noted to have worsening kidney function. Uveitis, which is an inflammation of certain tissues in the eye, will present as eye pain or redness.

Diagnosis

A physician might be able to make a diagnosis of possible interstitial nephritis on the basis of clinical presenting symptoms and signs alone. As noted above, however, not all symptoms or signs are necessarily present in all patients. In cases of drug-induced interstitial nephritis, the affected patient will typically come with a history of having started the culprit medication recently and a comparison of "before and after" kidney blood test results could be a potential diagnostic clue.

In cases where a diagnosis is not easily forthcoming, or if kidney function is severely reduced, a kidney biopsy might be necessary. This is an invasive test where a tiny piece of kidney's tissue needs to be taken and studied under a microscope.

Treatment

Once a definitive diagnosis of interstitial nephritis has been made, every attempt should be made to identify the inciting factor so that the cause of the inflammation may be removed, if possible. For instance, in cases of drug-induced interstitial nephritis, stopping the offending drug would be important, and the most common-sense first step. If no medications are implicated, then a search for other autoimmune and infectious agents should be pursued.

In patients with mild decline in kidney function, typically nothing more than stopping the offending agent is necessary. However, if significant inflammation-related decline in kidney function is seen, a trial of steroids might be helpful (in which case therapy might be needed for as long as 2-3 months). In patients who don't respond to steroids, another medication by the name of mycophenolate may be looked at as an alternative.

A Word From Verywell

Interstitial nephritis refers to acute or chronic inflammation being set off in the kidney due to various agents like medications, infections, or even autoimmune disease. Damage done to the kidney can range from mild reversible decline, to complete kidney failure. Identifying the underlying culprit that incited the inflammation is, therefore, the first step in treatment, but medications like steroids might be required.