What could be the cause of right-sided lower mid-back pain radiating to the abdomen, fever, and lack of response to Cipro (ciprofloxacin) in a patient with no urinary symptoms?

Right-Sided Lower Mid-Back Pain with Fever Unresponsive to Ciprofloxacin

This patient requires urgent abdominal imaging with CT scan of the abdomen and pelvis with IV contrast to evaluate for complicated pyelonephritis, renal abscess, or alternative intra-abdominal pathology given persistent fever despite 6 days of fluoroquinolone therapy. 1, 2

Immediate Diagnostic Approach

The clinical presentation of right-sided flank/back pain radiating to the abdomen with fever that has failed to respond to ciprofloxacin strongly suggests either:

• Complicated pyelonephritis (renal abscess, perinephric abscess, or obstructive pyelonephritis)
• Alternative intra-abdominal pathology (cholecystitis, appendicitis, diverticulitis, or other abscess)

Why Imaging is Mandatory Now

Persistent fever after 72 hours of appropriate antibiotic treatment for presumed pyelonephritis mandates imaging to rule out complications. 2 The European Urology guidelines specifically state that patients who remain febrile after 72 hours of treatment require additional investigations. 2 This patient has been on ciprofloxacin for 6 days without improvement—well beyond the 72-hour threshold.

95% of patients with uncomplicated pyelonephritis become afebrile within 48 hours, and nearly 100% within 72 hours of appropriate therapy. 2 This patient's persistent fever indicates either:

• Treatment failure due to resistant organism
• Complicated infection requiring drainage
• Wrong diagnosis entirely

Recommended Imaging Study

CT abdomen and pelvis with IV contrast is the most appropriate initial imaging study. 1 The ACR Appropriateness Criteria designate this as "usually appropriate" for acute nonlocalized abdominal pain with fever. 1

CT can identify:

• Renal or perinephric abscess 1, 2
• Urinary obstruction or stones 1, 2
• Emphysematous pyelonephritis 2
• Acalculous cholecystitis 1
• Appendicitis 1
• Diverticulitis with perforation 3
• Other intra-abdominal abscesses 1

Ultrasound is insufficient at this stage. While ultrasound can be used as initial imaging for suspected pyelonephritis, 2 this patient has already failed empiric antibiotic therapy and requires the comprehensive evaluation that only CT can provide. 1

Alternative Diagnoses to Consider

Hepatobiliary Disease

Acalculous cholecystitis is frequently unrecognized and can present with right-sided pain and fever. 1 Right upper quadrant pain may be absent in many patients. 1 Abdominal ultrasound can diagnose cholecystitis, cholelithiasis, and liver abscesses. 1

Appendicitis (Retrocecal)

Retrocecal appendicitis can present with right flank pain mimicking pyelonephritis. 1 CT with IV contrast has high sensitivity and specificity for appendicitis. 1

Complicated Pyelonephritis

Renal abscess formation occurs when microabscesses coalesce, particularly in high-risk patients or when treatment is delayed. 1 Risk factors include diabetes, immunocompromise, and urinary obstruction. 1, 2

Perinephric abscess can develop when a renal parenchymal abscess ruptures into the perinephric space. 1

Pyonephrosis (purulent material in an obstructed collecting system) often requires decompression for treatment success. 1

Diverticulitis with Retroperitoneal Perforation

Diverticulitis can present with back pain and fever, particularly if there is retroperitoneal perforation. 3 This can mimic pyelonephritis but requires surgical intervention. 3

Management Algorithm

Step 1: Obtain Urgent Imaging

• Order CT abdomen/pelvis with IV contrast immediately 1, 2
• Do not delay for ultrasound first given treatment failure 1

Step 2: Obtain Cultures Before Changing Antibiotics

• Urine culture and antimicrobial susceptibility testing 2, 4
• Blood cultures (given fever and possible bacteremia) 1, 4
• Complete blood count with differential 4

Step 3: Broaden Antibiotic Coverage

Switch from oral ciprofloxacin to IV broad-spectrum therapy while awaiting imaging and culture results. 2, 4

Recommended IV regimens:

• Ceftriaxone 1-2g IV once daily 2, 4
• Cefepime 1-2g IV every 12 hours (if severe or concern for resistant organisms) 1, 4
• Consider adding metronidazole if intra-abdominal source suspected 1

Step 4: Intervention Based on Imaging

• If abscess identified: Consult interventional radiology or surgery for drainage 1, 2
• If obstruction identified: Urgent urology consultation for decompression 1, 2
• If alternative diagnosis: Appropriate specialty consultation 1

Critical Pitfalls to Avoid

Do not continue oral ciprofloxacin without imaging. 2 Persistent fever after 6 days indicates treatment failure or complication requiring intervention.

Do not assume this is simple pyelonephritis. 2 The lack of urinary symptoms (no dysuria, frequency, or odor) makes uncomplicated UTI/pyelonephritis less likely. 1, 2

Do not delay imaging to try alternative oral antibiotics first. 2 This patient needs definitive diagnosis, not empiric treatment escalation.

Do not rely on ultrasound alone in this setting. 1 While ultrasound can identify some pathology, CT provides comprehensive evaluation needed after treatment failure. 1

Consider that ciprofloxacin resistance in E. coli is increasing. 5, 6 Treatment failure may indicate resistant organism requiring culture-directed therapy. 2