What is the differential diagnosis and initial management for a patient presenting with gastrointestinal (GI) pain?

Differential Diagnosis for Gastrointestinal Pain

Approach Based on Pain Location

For acute nonlocalized abdominal pain, CT abdomen and pelvis with IV contrast is the preferred initial imaging modality, as it alters diagnosis in 54% of patients and changes management in 42% of cases. 1

Right Lower Quadrant Pain

• Appendicitis is the primary consideration when fever and leukocytosis accompany RLQ pain 1
• Inflammatory bowel disease (Crohn's disease) presents with transmural inflammation, potential abscesses and fistulas, typically in terminal ileum and colon 1
• Ovarian pathology in women of childbearing age requires pelvic ultrasonography as first-line imaging 1
• CT sensitivity for appendicitis ranges from 85.7% to 100%, with specificity 94.8% to 100% 1

Left Lower Quadrant Pain

• Acute sigmoid diverticulitis should be suspected with the clinical triad of LLQ pain, fever, and leukocytosis 1
• Diverticulitis occurs in 10-20% of patients with diverticulosis, with 25% experiencing recurrence 1
• CT is the preferred test for evaluating suspected diverticulitis, identifying severity, extent, and complications including perforation, abscess, or fistula 1

Epigastric Pain

• Peptic ulcer disease presents with recurrent epigastric pain, potentially with occult blood in stool, vomiting, and retrosternal pain 2
• Gastroesophageal reflux disease causes heartburn and regurgitation 3
• Acute pancreatitis presents with severe epigastric pain radiating to the back 3
• Myocardial infarction must be excluded, especially with shortness of breath or chest pain 3
• Acute aortic syndromes may present with pain radiating to the back 3
• Upper endoscopy is the standard diagnostic test for suspected GERD, gastritis, PUD, or duodenal ulcer 3

Diffuse Abdominal Pain

• Bowel obstruction accounts for 15% of hospital admissions for acute abdominal pain and 20% of acute surgical cases 1
• Small bowel obstruction is caused by adhesions (55-75%), hernias, and neoplasms (90% combined) 1
• Large bowel obstruction is caused by cancer (60%), volvulus and diverticular disease (30%) 1
• Acute mesenteric ischemia presents as severe abdominal pain out of proportion to physical examination findings 1
• 95% of AMI patients present with abdominal pain, 44% with nausea, 35% with vomiting, 35% with diarrhea, 16% with blood per rectum 1

Functional Gastrointestinal Disorders

Irritable Bowel Syndrome

• IBS requires chronic, recurring abdominal pain or discomfort associated with disturbed bowel habit for at least 6 months 1
• Rome III criteria: recurrent abdominal pain at least 3 days per month in past 3 months, with improvement with defecation, onset associated with change in stool frequency, or onset associated with change in stool form 1
• Prevalence peaks in third and fourth decades with 2:1 female predominance in 20s-30s 1
• IBS affects approximately 1 in 4 people in the United States 4

Functional Dyspepsia

• Presents with chronic upper abdominal pain without structural abnormalities 4
• Explained by disordered gastrointestinal motility and sensation 4

Critical Red Flags Requiring Immediate Action

Perforation

• Sudden severe epigastric pain with fever and abdominal rigidity indicates perforation, which carries mortality up to 30% if treatment is delayed 2, 5
• CT findings include extraluminal gas, fluid or fat stranding, ascites, and focal wall defect 5
• Immediate surgical consultation is mandatory if peritoneal signs develop 2

Mesenteric Ischemia

• Severe abdominal pain out of proportion to examination findings should be assumed to be AMI until disproven 1
• Nearly 50% of embolic AMI patients have atrial fibrillation 1
• Physical exam demonstrating peritonitis indicates irreversible intestinal ischemia with bowel necrosis 1

Hemorrhage

• Hemorrhage is the most common complication of PUD (73% of complicated cases) with 30-day mortality of 8.6% 2
• Hematemesis suggests bleeding ulcer or malignancy 3

Initial Management Algorithm

Step 1: Localize Pain and Assess Severity

• Determine if pain is localized (RLQ, LLQ, epigastric) or diffuse 1
• Assess for peritoneal signs indicating perforation or advanced disease 1, 2

Step 2: Identify Alarm Features

• Weight loss, dysphagia, recurrent vomiting, GI bleeding, or family history of upper GI cancer mandate endoscopy 3
• Fever and leukocytosis suggest infectious/inflammatory process 1
• Hemodynamic instability requires immediate resuscitation 1

Step 3: Select Appropriate Imaging

• CT abdomen/pelvis with IV contrast for acute nonlocalized pain, suspected obstruction, diverticulitis, or mesenteric ischemia 1
• Pelvic ultrasonography for women of childbearing age with RLQ pain 1
• Upper endoscopy for epigastric pain with alarm features or suspected PUD/GERD 3, 2

Step 4: Targeted Treatment

• For suspected PUD: H. pylori testing and proton pump inhibitor therapy 3, 6
• Omeprazole is indicated for short-term treatment of active duodenal ulcer (4 weeks, with additional 4 weeks if needed) and active benign gastric ulcer (4-8 weeks) 6
• For bowel obstruction: NPO, IV fluids, nasogastric decompression, surgical consultation 1
• For diverticulitis: antibiotics for mild cases, surgical consultation for complicated cases 1
• For IBS: dietary modifications, symptom-targeted pharmacotherapy (avoid opioids), cognitive behavioral therapy for chronic pain 1, 4

Common Pitfalls to Avoid

• Never assume all epigastric pain is acid-related; always consider myocardial infarction, pancreatitis, or aortic dissection 3
• Do not rely solely on plain radiographs for acute abdominal pain evaluation, as they have limited diagnostic value 1
• Never assume benign peptic ulcer disease without histologic confirmation when ulceroproliferative features are present 5
• Do not use opioids for functional GI disorders or chronic abdominal pain 4
• Avoid NSAIDs in patients with peptic ulcer disease, as they worsen disease and increase bleeding risk 5
• Symptoms overlap extensively between GERD, gastritis, esophagitis, and PUD, requiring careful history and often endoscopic evaluation 2