What could be the cause of watery stools, dysuria, and right lower quadrant pain in a female adult with no known medical history?

Differential Diagnosis and Management of Watery Stools, Dysuria, and Right Lower Quadrant Pain

The most likely diagnosis in a previously healthy adult female presenting with this triad is infectious enterocolitis with concurrent urinary tract infection, though appendicitis with atypical presentation (including reactive diarrhea) must be urgently excluded. 1, 2

Immediate Diagnostic Approach

Obtain contrast-enhanced CT of the abdomen and pelvis immediately to differentiate between appendicitis, right colonic pathology (diverticulitis, inflammatory bowel disease), and other intra-abdominal causes while simultaneously evaluating the urinary tract. 1, 3 The American College of Radiology rates CT with IV contrast as "usually appropriate" (7-9/9) for right lower quadrant pain when the diagnosis is unclear, with sensitivity >95% for acute appendicitis. 1, 3

Critical Laboratory Testing

• Urinalysis with microscopy and urine culture to confirm UTI and identify causative organisms, as E. coli causes approximately 75% of UTIs in women. 1, 4
• Complete blood count to assess for leukocytosis suggesting intra-abdominal infection versus simple gastroenteritis. 1
• Pregnancy test in all women of childbearing age before imaging, as ectopic pregnancy can present with RLQ pain. 5

Most Likely Diagnostic Scenarios

Scenario 1: Infectious Gastroenteritis with Concurrent UTI (Most Common)

• Watery diarrhea from enterotoxigenic E. coli, Campylobacter, or Shigella species can occur simultaneously with ascending UTI from the same or different organisms. 6, 4
• Dysuria with frequency/urgency suggests uncomplicated cystitis, which manifests without fever in most cases. 7
• RLQ pain may represent colonic inflammation from infectious diarrhea rather than appendicitis. 2

Scenario 2: Appendicitis with Atypical Presentation (Cannot Miss)

• Appendicitis can present with diarrhea in 10-15% of cases due to pelvic appendix location causing rectal irritation or reactive ileocolitis. 2
• Dysuria occurs when inflamed appendix abuts the bladder or right ureter, causing urinary symptoms without true UTI. 1, 2
• CT sensitivity for appendicitis is 85.7-100% with specificity 94.8-100%. 1

Scenario 3: Right Colonic Diverticulitis or Inflammatory Bowel Disease

• Right-sided diverticulitis (more common in younger patients and Asian populations) presents with RLQ pain and can cause diarrhea. 2
• Crohn's disease involving the terminal ileum/cecum causes RLQ pain, diarrhea, and can produce fistulas to the bladder causing dysuria and pneumaturia. 1, 2

Treatment Algorithm Based on CT Findings

If CT Shows Appendicitis

• Proceed immediately to surgical consultation for appendectomy, as preoperative CT reduces negative appendectomy rates from 16.7% to 8.7%. 8
• Do not delay surgery for antibiotic treatment of concurrent UTI; perioperative antibiotics will cover both conditions. 1

If CT Shows Infectious Colitis Without Appendicitis

• Treat UTI empirically with nitrofurantoin 100mg BID for 5 days (first-line for uncomplicated cystitis with minimal resistance). 4, 7
• Alternative: fosfomycin 3g single dose or trimethoprim-sulfamethoxazole DS BID for 3 days if local resistance <20%. 4
• Avoid fluoroquinolones (ciprofloxacin) as first-line due to increasing resistance and collateral damage to normal flora. 6, 4
• Supportive care for gastroenteritis with hydration; antibiotics for diarrhea only if Shigella, Campylobacter, or severe symptoms. 6

If CT Shows Right Colonic Diverticulitis

• Outpatient management with oral antibiotics covering gram-negative and anaerobic organisms (ciprofloxacin 500mg BID plus metronidazole 500mg TID for 7-10 days) if no complications. 6, 2
• Admit if fever >38.5°C, unable to tolerate oral intake, or CT shows abscess/perforation. 2

If CT Shows Crohn's Disease

• Refer urgently to gastroenterology for disease staging and initiation of immunosuppressive therapy. 2
• If bladder fistula suspected (pneumaturia, fecaluria), surgical consultation required. 1, 2

Critical Pitfalls to Avoid

• Do not assume dysuria automatically means simple UTI when accompanied by RLQ pain and diarrhea; appendicitis with bladder irritation can mimic UTI. 1, 2
• Do not delay CT beyond 12 hours if appendicitis cannot be clinically excluded, as perforation increases morbidity and mortality. 3, 8
• Do not order non-contrast CT, as critical findings like bowel wall enhancement, abscess formation, and appendiceal perforation cannot be detected without IV contrast. 3, 8
• Do not treat empirically with antibiotics alone without imaging if appendicitis is possible; this delays diagnosis and increases perforation risk. 1
• Do not rely on urinalysis alone to guide management; pyuria can be present without infection (especially with appendiceal inflammation near bladder), and negative dipstick does not rule out UTI in symptomatic patients. 4, 7

When Imaging Cannot Be Obtained Immediately

If CT is unavailable within 2-4 hours and clinical suspicion for appendicitis is high (fever, leukocytosis >12,000, peritoneal signs):

• Transfer to facility with CT capability or proceed directly to surgical evaluation. 1
• Ultrasound has limited sensitivity (85%) for appendicitis in adults and should not delay definitive imaging. 1
• Do not discharge patient home without imaging if Alvarado score ≥7 or clinical concern remains high. 1