What are the differential diagnoses and treatment options for abdominal pain and vomiting?

Differential Diagnosis and Management of Abdominal Pain and Vomiting

Immediate Life-Threatening Conditions to Rule Out First

Begin by assessing for hemodynamic instability (tachycardia, hypotension, tachypnea) and peritoneal signs, as these indicate surgical emergencies requiring immediate intervention. 1

Critical Red Flags Requiring Emergency Surgical Consultation:

• Peritoneal signs (rebound tenderness, guarding, rigidity) suggest perforation or bowel necrosis 1
• Severe pain out of proportion to exam indicates acute mesenteric ischemia until proven otherwise 1
• Signs of shock (tachycardia, hypotension, cool extremities, altered mental status) mandate immediate surgical exploration 2, 1
• Bilious or feculent vomiting indicates mechanical obstruction requiring nasogastric decompression 1

Critical caveat: Absence of peritonitis does NOT exclude bowel ischemia—lactate and blood gas analysis are essential. 1

Structured Differential Diagnosis by Clinical Pattern

Mechanical Obstruction (Most Common Surgical Cause)

Small Bowel Obstruction:

• Adhesions (55-75% of cases): History of prior abdominal surgery has 85% sensitivity and 78% specificity for adhesive obstruction 2, 1
• Hernias (15-25%): Examine all hernia orifices (umbilical, inguinal, femoral) and surgical scars 2
• Malignancies (5-10%): Consider with unexplained weight loss and rectal bleeding 2

Large Bowel Obstruction:

• Colorectal cancer (60%): History of rectal bleeding and weight loss 2
• Volvulus (15-20%): Triad of abdominal pain, constipation, and vomiting, especially in elderly on psychotropic medications 1
• Diverticular stenosis (10%): Prior diverticulitis episodes 2

Gastroparesis and Functional Disorders

Gastroparesis mimics to consider: 2

• Cyclic vomiting syndrome: Episodic pattern with symptom-free intervals
• Cannabinoid hyperemesis syndrome: History of chronic cannabis use
• Rumination syndrome: Regurgitation within minutes of eating
• Functional dyspepsia: Overlap with gastroparesis symptoms
• Narcotic bowel syndrome: Chronic opioid use

Physical exam findings for gastroparesis: 2

• Succussion splash suggests delayed gastric emptying or gastric outlet obstruction
• Bruit in right upper quadrant suggests celiac artery compression syndrome
• Digital ulcers and telangiectasia suggest scleroderma
• Ascites, mass, or enlarged lymph nodes suggest underlying malignancy

Vascular Causes

Acute Mesenteric Ischemia:

• Severe abdominal pain with minimal physical findings 1
• Requires immediate CT angiography and surgical consultation 1
• Elevated lactate, metabolic acidosis, and marked leukocytosis are late findings 2

Celiac Artery Compression (Median Arcuate Ligament Syndrome):

• Postprandial pain pattern, age 40-60, weight loss >20 pounds predict successful surgical outcome 2
• Bruit on auscultation of right upper quadrant 2
• Diagnosis requires both clinical symptoms and imaging showing J-shaped celiac narrowing 2

Superior Mesenteric Artery Syndrome:

• Postprandial vomiting and abdominal pain 2, 3
• Symptoms relieved with positional changes 3
• Evaluate with small bowel follow-through or CT enterography 2

Mesenteric Venous Thrombosis:

• Accounts for 5-15% of mesenteric ischemia cases 2
• Nonspecific abdominal symptoms make clinical diagnosis difficult 2
• Diagnosed by CT or MR venography 2

Other Important Causes

Intestinal pseudo-obstruction: Diagnosed by symptoms, laboratory tests, and imaging studies showing dilated bowel without mechanical obstruction 2

Medication-induced: Opioids, anticholinergics, and other medications affecting peristalsis 2

Boerhaave's syndrome: Spontaneous esophageal rupture after excessive vomiting, presenting with sudden severe upper abdominal pain 4

Diagnostic Workup Algorithm

Step 1: Initial Assessment and Stabilization

• Vital signs: Check for tachycardia, hypotension, fever, tachypnea 2, 1
• IV fluid resuscitation: Aggressive crystalloid administration for dehydration 2, 1
• NPO status and nasogastric decompression: Mandatory for bilious vomiting or suspected obstruction 1

Step 2: Focused History

• Prior abdominal surgery: 85% sensitivity for adhesive obstruction 2, 1
• Timing of symptoms: Acute (<24 hours) vs. chronic (>1 month) 5, 6
• Relationship to meals: Postprandial pain suggests vascular insufficiency or SMA syndrome 2, 3
• Medication review: Opioids, anticholinergics, chemotherapy 2, 5
• Pattern of vomiting: Bilious suggests obstruction; timing after meals matters 1, 5

Step 3: Physical Examination

• Abdominal distension: Positive likelihood ratio 16.8 for obstruction 2
• Peritoneal signs: Indicate ischemia or perforation 2, 1
• Hernia examination: All orifices and surgical scars 2
• Digital rectal exam: Empty rectum suggests complete obstruction; blood suggests malignancy 2
• Gastroparesis-specific findings: Succussion splash, RUQ bruit, scleroderma signs 2

Step 4: Laboratory Testing

Essential initial labs: 2, 1

• Complete blood count
• Comprehensive metabolic panel (electrolytes, renal function)
• Arterial blood gas and lactate (critical for detecting ischemia)
• Liver function tests
• Amylase and lipase

Additional labs based on clinical suspicion: 2, 6

• Pregnancy test in women of childbearing age
• Thyroid-stimulating hormone
• Coagulation profile if surgery anticipated

Step 5: Imaging

Plain abdominal radiograph (initial test): 1, 7

• Sensitivity 74-84%, specificity 50-72% for obstruction
• In bedridden patients: Add left lateral decubitus view to detect pneumoperitoneum and air-fluid levels 7
• Critical limitation: Negative films do NOT exclude mesenteric ischemia or early obstruction 1

CT abdomen/pelvis with IV contrast (definitive test): 1, 7

• Sensitivity 93%, specificity 100%, accuracy 94% for obstruction 7
• Identifies transition point, bowel ischemia, and surgical causes 1
• Distinguishes mechanical obstruction from functional bloating 1
• For suspected mesenteric ischemia: CT angiography without delay 1

Specialized imaging: 2

• Mesenteric duplex ultrasound for celiac artery compression
• Small bowel follow-through or CT enterography for SMA syndrome
• Gastric emptying study if gastroparesis suspected (after ruling out anatomic causes)

Treatment Algorithm

For Suspected Bowel Obstruction:

1. Immediate supportive care: IV crystalloids, antiemetics, bowel rest 2, 1
2. Obtain CT to identify transition point and assess for ischemia 1
3. Serial abdominal exams every 4-6 hours to detect peritonitis 1
4. Surgical consultation if peritoneal signs, ischemia, or failure to improve 2, 1

For Suspected Mesenteric Ischemia:

1. Immediate CT angiography 1
2. Surgical consultation without delay 1
3. Systemic anticoagulation as bridge to definitive therapy (not monotherapy) 2
4. Transcatheter thrombolysis or embolectomy for arterial occlusion 2

For Gastroparesis (After Ruling Out Anatomic Causes):

Nausea/Vomiting Predominant: 2

• Mild: Dietary adjustments, antiemetics (ondansetron, promethazine, prochlorperazine, aprepitant) 2, 8
• Moderate: Antiemetics plus prokinetics (metoclopramide, domperidone, erythromycin, prucalopride), cognitive behavioral therapy 2
• Severe: Enteral feeding (J-tube), gastric electrical stimulation 2

Abdominal Pain Predominant: 2

• Treat as functional dyspepsia: acid-suppressive drugs (PPIs, H2 blockers), antispasmodics (hyoscyamine, dicyclomine, peppermint oil) 2
• Neuromodulators: tricyclic antidepressants, SSRIs, SNRIs, pregabalin, gabapentin 2
• Avoid opioids for abdominal pain treatment 2

Antiemetic Therapy:

Ondansetron (5-HT3 antagonist): 8

• Dosing: 8 mg every 8-12 hours for chemotherapy-induced nausea; 16 mg pre-op for postoperative nausea
• Contraindications: Congenital long QT syndrome, concomitant apomorphine use
• Warnings: Can mask progressive ileus or gastric distension following abdominal surgery—monitor for decreased bowel activity in patients with risk factors for GI obstruction 8
• Caution: QT prolongation, serotonin syndrome with concomitant serotonergic drugs 8

Common Pitfalls to Avoid

1. Assuming normal exam excludes ischemia: Lactate and blood gas are mandatory when ischemia suspected 1
2. Relying solely on plain radiographs: CT provides critical additional information about cause and complications 1, 7
3. Using antiemetics without considering obstruction: Ondansetron can mask progressive ileus—monitor bowel activity 8
4. Delaying surgical consultation: Signs of shock mandate immediate exploration 2, 1
5. Treating median arcuate ligament syndrome with stenting alone: Surgical ligament release should precede or accompany endovascular intervention 2
6. Using opioids for functional abdominal pain: Avoid in gastroparesis and functional disorders 2