What is the likely mechanism of pain in a patient with steady, aching abdominal pain localized to the right lower quadrant, worsened by coughing and movement?

Parietal Peritoneal Irritation (Somatic Pain)

The steady, aching pain precisely localized to the right lower quadrant and accentuated by coughing and movement is most consistent with parietal peritoneal irritation, also known as somatic pain. 1

Pain Mechanism Explanation

• Somatic pain arises from irritation of the parietal peritoneum, which is richly innervated with sensory nerve fibers that allow precise localization to a specific anatomic region. 1

• The key distinguishing features of parietal peritoneal pain include:

  • Precise localization to the affected area (in this case, the right lower quadrant) 1
  • Steady, aching quality rather than cramping or colicky 1
  • Accentuation by movement, coughing, or jarring due to stretching of the inflamed peritoneum 1

• This contrasts with visceral pain, which is typically poorly localized, dull, and cramping in nature, arising from distension or inflammation of hollow viscera. 2

Clinical Significance and Next Steps

• The presence of peritoneal signs (pain with coughing and movement) indicates the need for urgent imaging evaluation, typically with CT abdomen and pelvis with IV contrast. 1

• CT demonstrates 95% sensitivity and 94% specificity for appendicitis, which is the most common surgical cause of right lower quadrant pain with peritoneal signs. 1, 3

• CT identifies alternative diagnoses in 23-45% of cases, including diverticulitis, ileitis, colitis, bowel obstruction, ischemia, inflammatory bowel disease, and gynecologic pathology. 1, 3

Important Clinical Pitfall

• The absence of fever does not exclude serious pathology, as fever is absent in approximately 50% of appendicitis cases. 1

• The presence of localized peritoneal signs is a more reliable indicator of parietal peritoneal inflammation requiring further evaluation than systemic signs like fever. 1