A 48-year-old man comes to the emergency department due to fever and cellulitis of the distal right lower extremity. He was initially seen in a clinic 2 days earlier and treated with oral clindamycin, but he subsequently developed increasing erythema. Medical history is notable for nondeforming rheumatoid arthritis treated with hydroxychloroquine and a similar episode of cellulitis 2 years ago that resolved with a course of cefazolin. The patient is admitted to the hospital and treated with cefazolin and leg elevation. His fever rapidly resolves and the area of erythema recedes. However, 3 days after admission, serum creatinine increases from 1.2 to 1.9 mg/dL.
Urinalysis results are as follows:
Urine stain for eosinophils is negative.
Which of the following is the most likely diagnosis in this patient?

Question

A 48-year-old man comes to the emergency department due to fever and cellulitis of the distal right lower extremity.  He was initially seen in a clinic 2 days earlier and treated with oral clindamycin, but he subsequently developed increasing erythema.  Medical history is notable for nondeforming rheumatoid arthritis treated with hydroxychloroquine and a similar episode of cellulitis 2 years ago that resolved with a course of cefazolin.  The patient is admitted to the hospital and treated with cefazolin and leg elevation.  His fever rapidly resolves and the area of erythema recedes.  However, 3 days after admission, serum creatinine increases from 1.2 to 1.9 mg/dL.
Urinalysis results are as follows:
 Urine stain for eosinophils is negative.
Which of the following is the most likely diagnosis in this patient?

Quizplus · Accepted Answer

11ec193a_9721_b977_853d_15f64b9b41e8_MD0002_00 This patient has acute kidney injury (AKI) with pyuria, hematuria, and granular casts on urinalysis. In the setting of antibiotic therapy for cellulitis, this most likely represents antibiotic-induced acute interstitial nephritis (AIN). Drugs are the most common cause of AIN, implicated in up to 75% of cases. Major classes include antibiotics, proton pump inhibitors, and nonsteroidal anti-inflammatory drugs. Onset is generally within weeks to months after primary exposure but develops more rapidly (days) after repeat exposure. Characteristic features of AIN include rash (15%), fever (27%), and eosinophilia (23%), although patients rarely have all 3 and may be asymptomatic. Urinalysis commonly shows pyuria, hematuria, and white blood cell casts with varying degrees of proteinuria but may also be normal. Granular casts are noted in a variety of kidney pathologies and are nondiagnostic. Urinary eosinophils can be seen in up to 40% of patients with AIN, but they are present in a variety of diseases (eg, prostatitis, renal atheroemboli); therefore, their presence is supportive but nondiagnostic. Renal biopsy can confirm the diagnosis but is not required if renal function improves after the culprit drug is stopped. (Choice B) Although infectious processes can result in acute immune complex glomerulonephritis, this is usually associated with significant proteinuria and red blood cell casts. (Choice C) Prerenal AKI can develop in the setting of an acute illness but would not typically be associated with cells and casts on urinalysis. (Choices D and E) Renal involvement is rarely seen in rheumatoid arthritis and generally occurs in advanced, joint-destructive disease. Manifestations can include renal vasculitis, glomerulonephritis, or membranous nephropathy. Renal vasculitis and glomerulonephritis present with red blood cell casts, and membranous nephropathy causes significant proteinuria; neither finding is seen in this patient. Educational objective: Acute kidney injury after implementation of a new drug (especially antibiotics) should raise suspicion for acute interstitial nephritis. Symptom onset is variable and generally occurs weeks to months after primary exposure; however, symptoms develop more rapidly (days) after second exposure. The presence of white blood cell casts, urine eosinophils, hematuria, and pyuria are suggestive but not required for diagnosis. __________ References: Drug-induced acute interstitial nephritis. (http://www.ncbi.nlm.nih.gov/pubmed/20517290) Acute interstitial nephritis. (http://www.ncbi.nlm.nih.gov/pubmed/20336051)

A 48-Year-Old Man Comes to the Emergency Department Due to Fever