Chapter 3: Abdominal Pain Assessment & Differential Diagnosis

Abdominal pain serves as a critical diagnostic puzzle in primary care, requiring a systematic approach to differentiate acute surgical emergencies from chronic or self-limiting issues. This chapter outlines the physiological basis of abdominal discomfort, identifying tension from organ distention or muscle contraction, ischemia from restricted blood flow, and inflammation of the peritoneal lining as the three primary triggers for pain signals. A vital component of assessment involves distinguishing between visceral pain, which often presents as a deep, midline ache that causes patient restlessness, and parietal pain, which is sharp, well-localized, and typically forces a patient to remain immobile. The text emphasizes the importance of understanding referred pain, where shared neural pathways cause discomfort to be felt in distant sites, such as the right scapula during biliary events or the shoulder in cases of splenic rupture. Clinical evaluation centers on a rigorous history and physical exam, where clinicians must evaluate the timing of symptoms, such as whether vomiting occurs before or after the onset of pain, as this can indicate the necessity of surgical intervention. Diagnostic maneuvers are extensively covered, including the Murphy sign for gallbladder inflammation and specific muscle tests like the iliopsoas and obturator signs for appendicitis. Furthermore, the chapter highlights age-specific considerations, noting that children and older adults often exhibit atypical patterns that can mask serious pathologies like intussusception, malrotation, or mesenteric ischemia. The Apley rule is introduced for pediatric patients, suggesting that pain localized further from the umbilicus is more likely to have an organic cause. For diagnostic confirmation, a hierarchy of tools is presented, ranging from basic laboratory screenings like the complete blood count, pregnancy tests, and urinalysis to high-resolution imaging such as helical computed tomography and pelvic ultrasound. By covering a broad spectrum of differential diagnoses—including irritable bowel syndrome, pelvic inflammatory disease, and gastric ulcers—the material provides a foundational framework for clinical reasoning and evidence-based practice in the management of complex gastrointestinal and abdominal disorders.