An 18-year-old girl comes to the office with a new-onset skin rash and malaise. She is concerned as her aunt has lupus treated with corticosteroids. Her medical history is unremarkable except for dysuria and increased urinary frequency a week ago, which was effectively treated with sulfamethoxazole-trimethoprim. The patient takes no medications and uses no illicit drugs. She has had the same sexual partner for the past 4 months. Her temperature is 38.0 C (100.4 F), pulse is 86/min, and respirations are 16/min. Physical examination reveals a disseminated maculopapular rash. There is no costovertebral tenderness. The patient has no joint swelling or effusion. Her serum creatinine is 2.0 mg/dL. Urinalysis reveals 2-5 red blood cells/hpf, numerous white blood cell casts, and mild proteinuria. Which of the following is the most likely diagnosis?

Question

An 18-year-old girl comes to the office with a new-onset skin rash and malaise.  She is concerned as her aunt has lupus treated with corticosteroids.  Her medical history is unremarkable except for dysuria and increased urinary frequency a week ago, which was effectively treated with sulfamethoxazole-trimethoprim.  The patient takes no medications and uses no illicit drugs.  She has had the same sexual partner for the past 4 months.  Her temperature is 38.0 C (100.4 F), pulse is 86/min, and respirations are 16/min.  Physical examination reveals a disseminated maculopapular rash.  There is no costovertebral tenderness.  The patient has no joint swelling or effusion.  Her serum creatinine is 2.0 mg/dL.  Urinalysis reveals 2-5 red blood cells/hpf, numerous white blood cell casts, and mild proteinuria.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec25c8_d10d_4ff1_bc81_95900b5bd22d_MD0003_00 The clinical presentation is typical of allergic interstitial nephritis (AIN): acute renal failure, fever, rash, a recent history of para-aminobenzoic acid analogue antibiotic (sulfonamide) ingestion, and white blood cell (WBC) casts on urinalysis. Patients may also have arthralgias and eosinophiluria. Symptoms usually appear 5 days to several weeks after use of an offending agent. Drugs cause the majority of AIN cases; examples include antibiotics (eg, penicillins, cephalosporins, trimethoprim, rifampin), nonsteroidal anti-inflammatory drugs, and diuretics. Less commonly, AIN may be caused by infectious agents (eg, Legionella, Mycobacterium tuberculosis, Streptococcus). (Choice A) Disseminated gonococcemia causes a vesicopustular rash. Renal failure with WBC casts is not usually seen. (Choice C) The mucocutaneous manifestations of lupus include malar rash and discoid rash, but this patient has a maculopapular rash. Lupus nephritis is characterized by hypertension, mild proteinuria, and red blood cell (RBC) casts. (Choice D) Postinfectious glomerulonephritis produces hematuria, mild proteinuria, RBC casts, and fluid retention resulting in hypertension and periorbital edema. It usually occurs 1-2 weeks after an episode of streptococcal pharyngitis/skin infection and not after a urinary infection. (Choice E) Pyelonephritis can complicate untreated cystitis, but manifests with chills, fever, and tenderness in the flanks and/or the costovertebral angle. Disseminated rash is not usually seen. Educational objective: Drug-induced interstitial nephritis is usually caused by antibiotics (eg, penicillins, cephalosporins, trimethoprim, rifampin), nonsteroidal anti-inflammatory drugs, and diuretics. Patients present with a fever, maculopapular rash, and renal failure. Urinalysis may reveal white blood cell casts and, less frequently, eosinophils.

An 18-Year-Old Girl Comes to the Office with a New-Onset