What is the diagnosis and treatment for left-sided abdominal pain, bloating, and mushy stools?

Differential Diagnosis and Management of Left-Sided Abdominal Pain with Bloating and Mushy Stools

The most likely diagnosis is acute left-sided colonic diverticulitis, and you should obtain a CT abdomen/pelvis with IV contrast to confirm the diagnosis and distinguish between uncomplicated and complicated disease. 1, 2

Diagnostic Approach

Initial Clinical Assessment

• Left lower quadrant pain with bloating and altered bowel habits (mushy stools) strongly suggests acute diverticulitis, though irritable bowel syndrome and inflammatory bowel disease remain in the differential. 1, 2
• Physical examination should specifically assess for left lower quadrant tenderness, guarding, or peritoneal signs that would indicate complicated disease requiring urgent intervention. 1
• Do not rely on clinical symptoms and laboratory tests alone to make the diagnosis, as this approach has very low-quality evidence, particularly in elderly patients. 1

Imaging Strategy

• CT abdomen/pelvis with IV contrast is the gold standard diagnostic test, with 94% sensitivity and 99% specificity for acute left-sided diverticulitis. 1
• CT imaging is essential when diagnostic uncertainty exists and helps differentiate diverticulitis from colorectal cancer, inflammatory bowel disease, colitis, and other causes of left-sided pain. 1, 2
• If IV contrast is contraindicated (severe renal disease or contrast allergy), use ultrasound, MRI, or non-contrast CT as alternatives. 1, 2
• CT will identify complications including abscess, perforation, fistula, or free air that mandate different management strategies. 1, 2

Laboratory Testing

• Obtain complete blood count to assess for leukocytosis indicating infection or inflammation. 2
• C-reactive protein may be elevated but should not be used alone to rule in or rule out diverticulitis. 1

Management Based on CT Findings

Uncomplicated Diverticulitis (No Abscess, Perforation, or Peritonitis)

Most patients with uncomplicated disease can be managed as outpatients if they meet specific criteria. 1

Outpatient Management Criteria:

• Ability to tolerate oral intake 1
• Adequate social support at home 1
• No significant comorbidities 1
• Hemodynamically stable 1

Antibiotic Decision:

• In immunocompetent patients without sepsis-related organ failure, antibiotics may be avoided entirely for uncomplicated diverticulitis (WSES stage 0). 1
• Consider antibiotics if there are pericolic air bubbles or small amounts of pericolic fluid (WSES stage 1a). 1
• This represents a paradigm shift from historical practice, as moderate-certainty evidence shows no difference in outcomes between antibiotic and no-antibiotic approaches for truly uncomplicated disease. 1

Complicated Diverticulitis

Abscess Present (WSES Stage 1b-2a):

• Initiate broad-spectrum IV antibiotics immediately targeting gram-positive, gram-negative, and anaerobic organisms. 1, 3
• Regimen options include ceftriaxone plus metronidazole, or piperacillin-tazobactam. 3
• Add percutaneous drainage if abscess is >4 cm, with cultures obtained to guide antibiotic de-escalation. 1, 3
• Limit antibiotic duration to 3-5 days after adequate source control, maximum 4-7 days if clinically indicated. 1, 3

Free Air or Diffuse Peritonitis:

• Non-operative management is absolutely contraindicated—immediate surgical consultation is mandatory. 3, 4
• The presence of any free intraperitoneal air mandates operative intervention regardless of amount. 4
• Delay in surgical source control dramatically increases mortality. 3, 4

Alternative Diagnoses to Consider

Irritable Bowel Syndrome (IBS)

• If CT shows no diverticulitis or other structural pathology, consider IBS, particularly if symptoms are chronic and recurrent. 5, 6
• Mushy stools with bloating and left-sided pain fit the pattern of diarrhea-predominant or mixed IBS. 7, 6
• A low FODMAP diet may reduce abdominal pain and bloating in IBS patients. 7
• Antispasmodics including peppermint oil are first-line for abdominal pain in IBS. 7

Inflammatory Bowel Disease

• CT can identify bowel wall thickening, inflammatory changes, and complications suggesting Crohn's disease or ulcerative colitis. 2, 8
• Consider colonoscopy after acute symptoms resolve if inflammatory bowel disease is suspected. 8

Critical Follow-Up

Colonoscopy Timing

• Schedule colonoscopy 6-8 weeks after resolution of complicated diverticulitis in patients without recent colonoscopy (within past 1-2 years). 1, 3
• Colorectal cancer can present identically to diverticulitis with 10% imaging overlap, and colonoscopy is essential to exclude malignancy. 1
• For uncomplicated diverticulitis, colonoscopy is less critical if recent screening is up to date. 1

Red Flags Requiring Re-evaluation

• If symptoms persist beyond 5-7 days of appropriate antibiotics, obtain repeat imaging to assess for inadequate source control, abscess formation, or alternative diagnosis. 1, 3
• Recurrent symptoms immediately after completing antibiotics suggest treatment failure and warrant surgical consultation. 3

Common Pitfalls to Avoid

• Do not use antibiotics beyond 7 days without investigating for ongoing infection—prolonged courses increase C. difficile risk without improving outcomes. 1, 3
• Do not attempt conservative management when free air is present—this is associated with treatment failure and increased mortality. 3, 4
• Do not dismiss the diagnosis based on normal white blood cell count alone—diverticulitis can occur with normal inflammatory markers. 1
• Do not order colonoscopy during acute diverticulitis—this increases perforation risk and should be deferred until inflammation resolves. 1