WBR0380

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Renal
Prompt	[[Prompt::A 54 year old Caucasian male patient presents to the emergency department complaining of chills and dark-colored urine with back pain that radiates to the inguinal region. Upon further questioning, the patient was recently given trimethoprim-sulfamethoxazole (TMP-SMX) for a urinary tract infection. Patient’s vital signs reveal a temperature of 38.5 degrees C (101.3 degrees F), heart rate of 98 beats per minute, and blood pressure measuring 118/80 mmHg. Physical examination is significant for costovertebral angle tenderness bilaterally. After appropriate work-up, diagnosis of drug-induced interstitial nephritis is made. Which of the following is most the most important prognostic factor in the final outcome of the patient’s condition?]]
Answer A	AnswerA::Transformation of inflammatory lesions into fibrosis
Answer A Explanation	AnswerAExp::Transformation of interstitial cellular infiltrates into fibrosis is the most important prognostic factor in determining the outcome of AIN.
Answer B	AnswerB::Advanced patient age
Answer B Explanation	AnswerBExp::Generally, advanced patient age is an important factor in renal function since creatinine clearance normally declines with increasing age. However, age is not the most important factor for prognosis in AIN
Answer C	AnswerC::Dosage of offending medication
Answer C Explanation	AnswerCExp::Development of drug-induced AIN is not dose-related. Nonetheless, the time until discontinuing of the offending medications and delay in initiating steroid therapy are both important prognostic factors.
Answer D	AnswerD::Presence of urinary eosinophils
Answer D Explanation	[[AnswerDExp::Eosinophiluria is a common finding in drug-induced AIN. The finding might be useful in confirming the diagnosis, although false positive and false negative rates remain high. Eosinophiluria is not directly correlated with outcome of the disease.]]
Answer E	AnswerE::Ethnic background
Answer E Explanation	AnswerEExp::Ethnic background is not associated with outcome of AIN.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Acute interstitial nephritis (AIN) is a common cause of acute kidney injury. Drugs are the most common etiology of AIN, particularly antimicrobials and NSAIDs. The mainstay of treatment of drug-induced AIN is thus discontinuing the offending medication. As a result, recovery ranges widely, with approximately 50% of patients failing to fully recover into normal renal function. The most important factor in the determination of patients’ outcome is the rapid transformation of interstitial cellular infiltrates into fibrosis, which can be detected at least several days of interstitial inflammation. Educational Objective: Drug-induced acute interstitial nephritis is the most common cause of interstitial nephritis. Antimicrobials and NSAIDs are commonly attributed to drug-induced AIN. Transformation of interstitial cellular infiltrates into fibrosis is the most important prognostic factor in determining the outcome of AIN. References: Neilson EG. Mechanisms of disease: Fibroblasts – a new look at an old problem. Nat Rev Nephrol. 2006; 2:101-107 Praga M, Gonzalez E. Acute Interstitial Nephritis. Kidney International. 2010; 77:956-961 Educational Objective: References: ]]
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