This page is dedicated to organizing various examples of standardized exam questions whose answer is acute interstitial nephritis. While this may seem a odd practice, it is useful to see multiple examples of how acute interstitial nephritis will be characterized on standardized exams (namely the boards and the shelf exams). This page is not meant to be used as a traditional question bank (as all of the answers will be the same), however seeing the classic “test” characterization for a disease is quite valuable.
KEY CHARACTERISTICS OF THIS CONDITION (ON EXAMS)
When it comes to standardized exams, each topic has its own “code” marked by key buzzwords, lab findings, clues, etc. If you are well versed in this code you will be able to more quickly identify the condition that is being discussed, and get the right answer on the exam you are taking. Below is the “code” for acute interstitial nephritis.
- Fever and rash are often present. However patients may be asymptomatic as well.
- Hematuria is often present
- Recent medication usage with this condition as a side effect: Penicillins, beta-lactam antibiotics (ampicillin) furosemide, NSAIDs, proton pump inhibitors, sulfa drugs
- Might occur secondary to certain disease (less classical presentation): mycoplasma infection, Sjogren syndrome, SLE, sarcoidosis
- Fever may be detected when taking vitals
- Hematuria can be detected on urinalysis
- Pyuria: classically eosinophils will be in the urine (A VERY SPECIFIC FINDING)
Question # 1
30-year-old male comes to the clinic because he has been experiencing fever and joint pains for one day. He is currently being treated with cephalexin for a skin infection. Recently he has noticed that his urine has turned darker. His temperature is 101.4°F, blood pressure is 130 over 70 mmHg, pulse is 90 bpm, and respirations are 15/min. A physical exam shows a skin rash but is otherwise unremarkable. Urine analysis shows 10 RBCs/HPF, 12 WBCs/HPF, white cell casts, eosinophiluria, and mild proteinuria. The patient’s BUN is 42 mg/dl and a serum creatinine is 2.3 mg/dl. What is the likely diagnosis in this patient?
Explanation # 1
Fever + rash + hematuria + WBC casts + eosinophiluria + recent cephalosporin usage = acute interstitial nephritis (drug-induced)
Question # 2
A 50 year old man comes to the clinic because he has a fever and skin rash. One week ago he was treated with ampicillin for a bacterial sinus infection. He also explains that he has low urine output. His temperature is currently 99.6°F, blood pressure is 125/70 mm Hg, and his heat rate is 85 bpm. A physical exam shows a maculopapular rash diffusely. The pateint’s serum creatinine is currently 2.6 mg/dL. A urine sediment reveals the presence of 5-10 RBCs/hpf, 5-10 WBCs/hpf, and 3-5 eosiniphils/hpf. What might the patient be suffering from?
Explanation # 2
Recent ampicillin usage + fever + rash + hematuria + eosinophiluria = acute interstitial nephritis (drug-induced)
A 40 year old woman comes tot he clinic because she has been suffering from a fever and joint pain for the past week. She expulsion that she has chronic headaches and that she takes ibuprofen several times a day to control her pain. A physical exam shows the presence of a diffuse maculopapular rash, but is otherwise unremarkable. A urinalysis reveals 2+ protein, 10-20 WBC/hpf, and the presence of eosinophils. A renal biopsy is performed in this patient to assist with the diagnosis. What is the probable diagnosis in this patient?
Fever + rash + hematuria + eosinophiluria = acute interstitial nephritis
A 20 year old female comes to her primary care physician because she has been experiencing a progressive fever, malaise, and blood in her urine after she began taking an oral antibiotic for a UTI a week ago. She explains that she also has had a 3 day history of a rash. Her vitals are as follows: temperature of 100.°F, heart rate of 80 bpm, respiration rate of 15/min, and a blood pressure of 132/85 mm Hg. A physical exam shows a petechial rash that is present diffusely. A urinalysis is performed and the results are below:
- Blood: 3+
- Protein: 2+
- Leukocytes: 120-130/hpf
- Eosinophils: 30%**
What is the most likely diagnosis in this patient?
Fever + rash + hematuria + recent history of antibiotic usage + eosinophiluria = acute interstitial nephritis
TESTABLE FACTS ABOUT THIS TOPIC (BEYOND ITS IDENTIFICATION)
Many questions on standardized exams go beyond simply recognizing the underlying topic. Often there are specific testable facts regarding some aspect of the topic’s pathophysiology/management/clinical implications that are commonly asked. Some of these are listed below:
- Histological findings expected on kidney biopsy: inflammatory infiltrates in the interstitium.
- Treatment: cessation of the offending medication.
Page Updated: 02.13.2017