What is the diagnosis and management for a young male presenting with left-sided abdominal pain and diarrhea?

Left-Sided Abdominal Pain and Mushy Stools in a Young Male

The most likely diagnosis is acute left-sided colonic diverticulitis, and you should obtain a CT scan with contrast to confirm the diagnosis and assess for complications. 1

Initial Diagnostic Approach

Clinical Presentation Assessment

Left-sided abdominal pain with diarrhea ("mushy stools") in a young male raises several diagnostic possibilities, but acute diverticulitis is increasingly common in younger patients—up to one-fifth of acute diverticulitis cases occur in patients under 50 years of age. 1

When to Order CT Imaging

You should use abdominal CT imaging with oral and intravenous contrast when diagnostic uncertainty exists, which is appropriate in this case given the nonspecific presentation. 1 CT has excellent diagnostic accuracy with 94% sensitivity and 99% specificity for acute diverticulitis. 1 Clinical diagnosis alone is correct in only 40-65% of patients, making imaging essential for confirmation. 1

Key Laboratory Studies

Order complete blood count, C-reactive protein (CRP), and inflammatory markers. 1 Elevated CRP >140 mg/L or white blood cell count >15 × 10⁹ cells/L indicates higher risk for complicated disease and may influence treatment decisions. 2

Classification and Risk Stratification

Uncomplicated vs. Complicated Disease

CT findings will determine whether this is uncomplicated diverticulitis (localized inflammation only) or complicated disease (abscess, perforation, fistula, obstruction, or bleeding). 1 Approximately 88% of cases are uncomplicated, while 12% present with complications. 1

High-Risk Features to Identify

Look for CT findings of pericolic extraluminal air, fluid collection, or longer segments of inflammation—these predict progression to complicated disease. 1 Clinical features suggesting higher risk include symptoms lasting >5 days, vomiting, pain score ≥8/10, and ASA score III or IV. 1, 2

Management Algorithm

For Uncomplicated Diverticulitis in Immunocompetent Patients

Most young, immunocompetent patients with uncomplicated diverticulitis do NOT require antibiotics. 1, 2 Multiple high-quality randomized trials, including the DIABOLO trial with 528 patients, demonstrate that antibiotics neither accelerate recovery nor prevent complications or recurrence in uncomplicated cases. 1

Outpatient Management Criteria

You can manage this patient as an outpatient if he meets ALL of the following: 1, 2

• Can tolerate oral fluids and medications
• No significant comorbidities or frailty
• Adequate home and social support
• Temperature <100.4°F
• Pain controlled with acetaminophen alone
• No signs of systemic inflammatory response or sepsis

Treatment Without Antibiotics

Prescribe supportive care consisting of: 1, 3

• Clear liquid diet during acute phase, advancing as tolerated
• Adequate hydration
• Acetaminophen for pain control (avoid NSAIDs)
• Mandatory re-evaluation within 7 days, sooner if symptoms worsen 1, 2

When Antibiotics ARE Indicated

Reserve antibiotics for patients with ANY of these features: 1, 2

• Immunocompromised status (steroids, chemotherapy, transplant)
• Age >80 years
• Pregnancy
• Persistent fever or chills
• Increasing leukocytosis
• CRP >140 mg/L or WBC >15 × 10⁹ cells/L
• Vomiting or inability to maintain hydration
• Symptoms lasting >5 days
• CT findings of fluid collection or longer inflamed segment
• Significant comorbidities (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes)

Antibiotic Regimens When Needed

Outpatient oral regimen (4-7 days): 1, 2

• First-line: Ciprofloxacin 500 mg twice daily PLUS metronidazole 500 mg three times daily
• Alternative: Amoxicillin-clavulanate 875/125 mg twice daily

Inpatient IV regimen: 1, 2

• Ceftriaxone PLUS metronidazole, OR
• Piperacillin-tazobactam
• Transition to oral antibiotics as soon as patient tolerates oral intake

For Complicated Diverticulitis

Hospitalize immediately and initiate IV antibiotics. 1, 2

Abscess Management

• Small abscesses (<4-5 cm): IV antibiotics alone for 7 days 1, 2
• Large abscesses (≥4-5 cm): Percutaneous CT-guided drainage PLUS IV antibiotics 1, 2
• Antibiotic duration after drainage: 4 days for immunocompetent patients with adequate source control; up to 7 days for immunocompromised or critically ill patients 1

Surgical Consultation

Obtain urgent surgical consultation for: 1, 2

• Generalized peritonitis
• Sepsis or hemodynamic instability
• Failed medical management
• Inability to drain abscess percutaneously

Alternative Diagnoses to Consider

While diverticulitis is most likely, maintain awareness of other possibilities in a young male with left-sided pain and diarrhea:

Inflammatory Bowel Disease

Consider Crohn's disease or ulcerative colitis, especially if there is rectal bleeding, weight loss, or extraintestinal manifestations. 1 CT can help differentiate, but colonoscopy may be needed after acute symptoms resolve. 1

Infectious Colitis

Obtain stool studies if there is high fever, bloody diarrhea, or recent antibiotic use suggesting Clostridioides difficile infection. 1

Irritable Bowel Syndrome

Less likely given acute presentation, but IBS typically presents with chronic symptoms, bloating that worsens throughout the day, and pain relieved by defecation. 4

Follow-Up Care

Colonoscopy Timing

Perform colonoscopy 6-8 weeks after symptom resolution (or longer if symptoms persist) for: 1, 2

• First episode of uncomplicated diverticulitis (if no high-quality colonoscopy within past year)
• Any episode of complicated diverticulitis (7.9% risk of underlying malignancy)
• Patients >50 years requiring routine screening

Prevention of Recurrence

Counsel the patient on lifestyle modifications: 1, 2

• High-quality diet: High in fiber from fruits, vegetables, whole grains, legumes (>22.1 g/day); low in red meat and sweets
• Regular vigorous physical activity
• Achieve/maintain normal BMI (18-25 kg/m²)
• Smoking cessation
• Avoid nonaspirin NSAIDs when possible
• Do NOT restrict nuts, corn, popcorn, or small-seeded fruits (no evidence of harm) 1, 2

Critical Pitfalls to Avoid

Do not routinely prescribe antibiotics for uncomplicated diverticulitis in young, immunocompetent patients—this contributes to antibiotic resistance without clinical benefit. 1, 2

Do not assume all patients require hospitalization—outpatient management is safe and cost-effective (35-83% cost savings) for appropriate candidates. 1, 3

Do not delay CT imaging in diagnostic uncertainty—clinical diagnosis alone misses 35-60% of cases and may miss alternative diagnoses requiring different management. 1

Do not stop antibiotics early if they are indicated—complete the full 4-7 day course even if symptoms improve. 2

Do not fail to arrange mandatory follow-up within 7 days—approximately 5% of patients develop smoldering diverticulitis or progress to complicated disease. 1, 2