Acute interstitial nephritis

Disease Description (Causes and Symptoms)

• Summary of definition: Acute tubulo-interstitial nephritis is a disease in which inflammatory cells infiltrate the tubules and the interstitium between them, causing an acute decline in kidney function.
• Causes
  • Medications (approximately 75%): antibiotics (beta-lactams, sulfonamides, etc.), nonsteroidal anti-inflammatory drugs (NSAIDs), some diuretics, acid-suppressing drugs (PPIs), antigout medication (allopurinol), etc., as well as folk remedies (traditional herbal medicines, etc.).
  • Systemic immune diseases (approximately 15%): e.g., systemic lupus erythematosus (SLE).
  • Infections (approximately 10%): caused by bacterial or viral infections, etc.
• Pathophysiology: Inflammatory cells (lymphocytes, eosinophils, monocytes, etc.) infiltrate the interstitium due to a drug or immune response, causing interstitial edema and tubular injury. In severe cases, fibrosis may progress and lead to chronic kidney damage.
• Main symptoms (including statistical findings)
  • Typical symptoms: fever (approximately 30%), rash (approximately 20%), joint pain (approximately 45%), back pain, hypertension, proteinuria, and hematuria (gross hematuria approximately 5%).
  • Urinary findings: decreased urine output (oliguria) in approximately 50%, and detection of leukocytes and eosinophils in the urine (eosinophilia approximately 30%).
  • Sometimes it is asymptomatic and is discovered through elevated kidney function indicators (BUN/creatinine) on blood tests.
• Onset: Symptoms and decreased kidney function often develop within days to several weeks after administration of the causative medication.

Treatment

• Basic principles
  • Immediately discontinue the causative medication, when possible.
  • If an infection or systemic disease is the cause, provide appropriate treatment for that condition.
• Drug treatment
  • Steroids (e.g., prednisone): often used clinically to promote recovery of kidney function (the dose and duration are determined according to the patient's condition). In general, the dose is gradually tapered after an initial high dose depending on the severity and course.
  • Immunosuppressants: considered rarely when an autoimmune condition is the primary cause and the response to steroids is insufficient.
• Supportive treatment
  • Electrolyte and fluid management; dialysis when necessary (in the presence of electrolyte imbalance, fluid overload, or uremia due to acute kidney failure).
  • Avoidance of nephrotoxic drugs, blood pressure control, adjustment of protein intake, etc.
• Diagnostic considerations
  • Kidney tissue examination (biopsy): may be necessary for definitive diagnosis (interstitial infiltration, interstitial edema, and, in some cases, assessment of fibrosis).
  • Tests: blood tests (creatinine, BUN, electrolytes, and confirmation of eosinophilia on CBC), urinalysis (urine sediment, proteinuria, hematuria, urinary leukocytes/eosinophils), and kidney ultrasound (to rule out obstructive disease).
• Lifestyle management and precautions
  • Avoid the causative medication or potentially nephrotoxic drugs, especially NSAIDs.
  • Maintain adequate fluid intake and regularly monitor kidney function (creatinine).
  • When using steroids, monitor for adverse effects such as infection, high blood glucose, and osteoporosis.
• Complications and prognosis
  • If the cause is removed and treatment is provided in a timely manner, kidney function can recover in many cases.
  • If discontinuation of the causative medication is delayed or interstitial fibrosis is severe, the condition may progress to chronic kidney failure.
  • In severe cases, continuous dialysis therapy may be necessary.

Checklist Before an Outpatient Visit (Including Items to Prepare and Sample Questions)

• Items to prepare (before visiting the hospital)
  • A list of all medications currently being taken (including prescription drugs, over-the-counter drugs, traditional herbal medicines, and health functional foods), along with when they were started and their dosages
  • Copies or reports of recent test results (blood tests, urinalysis, kidney ultrasound, etc.)
  • A record of when symptoms began and how they have progressed (fever, rash, changes in urine output, back pain, etc.)
  • Past medical history (especially kidney disease, autoimmune disease, and any recent history of infection)
  • Allergy history (including drug allergies) and whether pregnancy is possible
• Key information to tell the doctor at the hospital
  • Any medications that were started recently among those currently being taken (especially antibiotics, NSAIDs, PPIs, traditional herbal medicines, etc.)
  • Changes in urine color or amount, and whether fever, rash, or joint pain are present
  • Any recent infection (respiratory, urinary tract, etc.) or worsening of a systemic disease

General Sample Questions to Ask the Doctor

• "How much has my kidney function declined (based on my most recent creatinine level)?"
• "Which of the medications I am currently taking should I stop? Is there an alternative medication?"
• "Why do I need to take steroids, and what are the expected duration and side effects?"
• "Do I need a kidney biopsy? What are the risks and benefits of the test?"
• "How much recovery of kidney function can be expected after treatment? How will long-term follow-up be managed?"

Disease-Specific Sample Questions

• "Is the [medication name] I am taking highly likely to have caused this disease? If so, what alternative medication would you recommend?"
• "How would a kidney biopsy change the treatment plan (e.g., whether to start steroids)? Can steroids be started without the biopsy?"