Infectious Disease · Urinary Tract Infections
The facts most likely to be tested
Escherichia coli is the most common causative pathogen in acute pyelonephritis.
Clinical diagnosis is supported by the triad of fever, flank pain, and costovertebral angle (CVA) tenderness.
Urinalysis typically reveals pyuria, bacteriuria, and pathognomonic white blood cell (WBC) casts.
Imaging is reserved for patients with sepsis, persistent high fever after 48-72 hours of treatment, or suspected nephrolithiasis.
Non-contrast CT of the abdomen and pelvis is the gold standard imaging modality to evaluate for complications like renal abscess or obstruction.
Outpatient management for uncomplicated cases involves oral fluoroquinolones (e.g., ciprofloxacin) or trimethoprim-sulfamethoxazole.
Inpatient management for severe or pregnant patients requires intravenous ceftriaxone or aminoglycosides.
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A 28-year-old female presents to the emergency department with a 3-day history of fever, chills, and right-sided flank pain. She reports associated nausea and dysuria. On physical examination, she is febrile at 102.2°F (39°C) and exhibits significant right costovertebral angle tenderness. Urinalysis demonstrates nitrite positivity, leukocyte esterase, and WBC casts on microscopy.
What is the most likely diagnosis?
Acute pyelonephritis
The presence of systemic symptoms (fever) combined with flank pain and the pathognomonic finding of WBC casts on urinalysis confirms the diagnosis of acute pyelonephritis.
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Etiology / Epidemiology
Ascending infection from E. coli is the primary cause. Pregnancy and anatomical obstruction are critical risk factors.
Clinical Manifestations
Triad of fever, flank pain, and costovertebral angle tenderness. Look for pyuria and WBC casts.
Diagnosis
Urinalysis showing pyuria/WBC casts is diagnostic. Urine culture is the gold standard for pathogen identification.
Treatment
Outpatient: Ciprofloxacin or Levofloxacin. Avoid fluoroquinolones in pregnancy.
Prognosis
Most recover with antibiotics. Sepsis and renal abscess are the primary life-threatening complications.
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Epidemiology & Etiology
Most cases result from ascending lower urinary tract infections, with E. coli accounting for >80% of pathogens. Pregnancy significantly increases risk due to ureteral dilation and urinary stasis. Other risk factors include vesicoureteral reflux, neurogenic bladder, and recent instrumentation.
Pertinent Anatomy
Infection involves the renal parenchyma and the renal pelvis. The proximity of the ureterovesical junction allows for the retrograde migration of bacteria from the bladder to the kidneys.
Pathophysiology
Bacteria colonize the periurethral area and ascend via the ureters to the renal pelvis. This triggers an inflammatory response, leading to edema and potential tissue necrosis. The presence of WBC casts confirms the infection is localized to the renal tubules rather than the bladder.
Clinical Manifestations
Patients present with acute onset of fever, chills, and unilateral or bilateral costovertebral angle tenderness (CVA tenderness). Systemic symptoms like nausea and vomiting are common. Red flags include signs of sepsis, hypotension, or altered mental status, which necessitate immediate inpatient admission.
Diagnosis
The urinalysis typically reveals pyuria, bacteriuria, and pathognomonic WBC casts. A urine culture is the gold standard to guide targeted therapy. Imaging, such as a CT abdomen/pelvis without contrast, is reserved for patients who fail to improve within 48-72 hours or have suspected obstruction.
Treatment
Outpatient management for stable patients involves Ciprofloxacin or Levofloxacin for 7 days. Fluoroquinolones are contraindicated in pregnancy; use Ceftriaxone or Nitrofurantoin instead. Inpatient management requires IV Ceftriaxone or an aminoglycoside until the patient is afebrile for 24 hours.
Prognosis
Most patients respond to therapy within 48 hours. Renal abscess or emphysematous pyelonephritis (gas-forming infection) are rare but severe complications. Patients with diabetes or structural abnormalities require closer monitoring for sepsis.
Differential Diagnosis
Nephrolithiasis: absence of fever and WBC casts
Pelvic Inflammatory Disease: presence of cervical motion tenderness
Appendicitis: localized to the right lower quadrant
Ectopic Pregnancy: positive beta-hCG
Cystitis: absence of systemic symptoms and CVA tenderness