A 52-year-old woman with a history of diabetes mellitus and hypertension presents to the Emergency Department with fevers, chills, and abdominal pain. The symptoms began about 1 week ago and have been getting worse. The abdominal pain is associated with nausea and vomiting, and she has not been able to eat. On examination, her temperature is 38.8°C, blood pressure is 104/68 mmHg, heart rate is 94 beats per minute, and respiratory rate is 16 breaths per minute. Her abdominal examination shows right-sided pain to deep palpation, and she has severe right-sided costovertebral angle tenderness. Her laboratory values are shown below.
A urine culture returns positive for E. coli that is sensitive to ceftriaxone and ciprofloxacin. She is treated with IV ceftriaxone, but after 3 days of treatment she continues to be febrile.
What is the most appropriate next step in management?
A. Renal biopsyCT scan with contrast. This patient has pyelonephritis that likely progressed to a renal or perinephric abscess, which is indicated by the persistent fever. Patients with this complication will present with symptoms typical of pyelonephritis (fevers, chills, flank pain, abdominal pain, anorexia, nausea/vomiting), but will continue to be febrile despite treatment with appropriate antibiotics. Most cases of renal/perinephric abscesses are caused by urologic pathogens (e.g., E. coli and other enteric gram-negative bacilli); however, S. aureus is also common and arrives at the kidneys by hematogenous spread. The best diagnostic test is a CT scan of the abdomen with contrast, although a renal ultrasound can also identify many renal/perinephric abscesses. If the abscess is small, it can be observed with antibiotics alone; if the patient does not respond to antibiotics, or if the abscess is large, both antibiotics and drainage are necessary. Antibiotic therapy should always be based on culture and sensitivity data when available; however, empiric therapy for renal/perinephric abscesses is the same as for pyelonephritis. Options include a fluoroquinolone, ceftriaxone, ampicillin-sulbactam, an aminoglycoside, or anti-staphylococcal antibiotics if S. aureus is suspected.
(A) WBC casts do not necessarily indicate acute interstitial nephritis or glomerulonephritis; they may also indicate an upper UTI such as pyelonephritis. Therefore, a renal biopsy is not the next step. (C) Failure to defervesce after treatment with antibiotics raises the concern for a complication of pyelonephritis, such as a renal or perinephric abscess, and therefore further diagnostic workup should be pursued. (D) The organism is sensitive to both antibiotics, so there is no benefit of changing antibiotics.