Abdominal pain differential diagnoses:
Abdominal pain is a high-yield topic on USMLE Step 1, Step 2 CK, and Step 3.
Mastering its differential diagnosis is essential for excelling in clinical practice and ensuring success on exam day. Understanding the type, location, and associated symptoms of abdominal pain can help you quickly narrow down potential diagnoses.
Understanding the Types of Abdominal Pain
Abdominal pain can be classified into visceral, parietal, and referred pain, each with distinct characteristics.
Visceral pain is often dull and poorly localized, commonly seen in conditions like early appendicitis, gastroenteritis, or bowel obstruction.
Parietal pain, on the other hand, is sharp and well-localized, typical in late-stage appendicitis, peritonitis, or diverticulitis.
Referred pain occurs when pain is felt at a site distant from the affected organ, such as shoulder pain from diaphragmatic irritation or back pain from pancreatitis or an aortic aneurysm.
Differential Diagnosis Based on Pain Location
Right Upper Quadrant (RUQ) Pain
Pain in this region often suggests hepatobiliary disease.
Cholecystitis presents with RUQ pain, fever, nausea, and a positive Murphy’s sign on physical exam.
Biliary colic causes postprandial RUQ pain without fever or leukocytosis, distinguishing it from cholecystitis.
Hepatitis may cause dull RUQ pain with jaundice and elevated liver enzymes.
Left Upper Quadrant (LUQ) Pain
LUQ pain is less common but can be caused by splenic rupture, typically following trauma, and often accompanied by left shoulder pain.
Gastritis and peptic ulcer disease also manifest with LUQ or epigastric discomfort, worsened by NSAIDs or stress.
Right Lower Quadrant (RLQ) Pain
Appendicitis remains the most important diagnosis in RLQ pain. It starts as periumbilical discomfort before localizing to the RLQ with associated fever, nausea, and rebound tenderness. Ovarian torsion is a must-not-miss differential in female patients presenting with sudden, severe RLQ pain and an adnexal mass. Ectopic pregnancy should also be considered in any woman of reproductive age with RLQ pain and a positive β-hCG test.
Left Lower Quadrant (LLQ) Pain
LLQ pain in an older patient with fever and altered bowel habits often indicates diverticulitis, which requires confirmation via CT scan. Ischemic colitis can also present with LLQ pain and bloody diarrhea, often in patients with cardiovascular risk factors.
Epigastric Pain
Pain in the epigastric region often relates to pancreatitis, GERD, or myocardial infarction (MI). Pancreatitis presents with severe, radiating pain to the back, nausea, vomiting, and elevated lipase or amylase. GERD manifests as burning epigastric pain, worsened with lying down, and relieved by antacids. Atypical MI should always be ruled out, particularly in diabetic or elderly patients presenting with epigastric discomfort.
Diffuse Abdominal Pain
When pain is generalized, conditions like gastroenteritis, bowel obstruction, or mesenteric ischemia should be considered. Gastroenteritis is associated with nausea, vomiting, and diarrhea, often with a viral etiology. Bowel obstruction presents with cramping pain, abdominal distension, and high-pitched bowel sounds.
Mesenteric ischemia, a life-threatening emergency, manifests with severe pain out of proportion to exam findings, often in patients with atrial fibrillation or vascular disease.
Key Diagnostic Clues and Imaging
In the USMLE, clinical vignettes often emphasize history, physical exam findings, and key diagnostic tests to help differentiate causes of abdominal pain. CT imaging is the preferred modality for appendicitis, diverticulitis, and mesenteric ischemia, while ultrasound is used for hepatobiliary disorders like cholecystitis and biliary colic. Lab tests such as lipase for pancreatitis, liver function tests for hepatitis, and β-hCG for ectopic pregnancy are frequently tested.
High-Yield USMLE Takeaways
Pain with rebound tenderness suggests peritonitis and requires immediate surgical evaluation.Pain that radiates to the back may indicate pancreatitis or aortic aneurysm rupture.
Postprandial pain is characteristic of biliary colic or mesenteric ischemia.
RLQ pain with fever and nausea is appendicitis until proven otherwise.
Elderly patient with severe hypotension and sudden pain raises suspicion for AAA rupture.
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