A 21-year-old man comes to the emergency department due to abdominal pain, nausea, and vomiting. The patient started having vague periumbilical pain in the morning. Over the next several hours, the pain became more severe, sharper, and localized to the right lower abdominal quadrant. Temperature is 38.3 C (100.9 F), blood pressure is 132/84 mm Hg, pulse is 102/min, and respirations are 12/min. Physical examination shows maximal tenderness in the right lower abdomen two-thirds of the distance from the umbilicus to the anterior superior iliac spine. Bowel sounds are decreased. Laboratory studies reveal a leukocyte count of 16,000/mm³. The change in this patient's pain characteristics is most likely explained by which of the following?

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11ec160b_3579_f96e_9249_8d2b2419a232_MD0001_00 This patient's presentation is concerning for appendicitis, which can cause both visceral (vague, nonlocalized) and somatic (sharp, well-localized) abdominal pain. Visceral abdominal pain is most often due to luminal distension and stretching of smooth muscle and is carried by general visceral afferent fibers of the autonomic nervous system. The pain typically occurs in the midline region and is poorly localized and of a dull, constant, or cramping quality. Patients with visceral pain also commonly develop nausea, vomiting, or sweating due to activation of the autonomic nervous system. In contrast, somatic pain is usually due to irritation of the parietal peritoneum and is well localized, more severe, and worsened with deep inspiration or pushing on the abdominal wall. The afferent pain fibers for the appendix, proximal colon (including the cecum), and overlying visceral peritoneum cross through the superior mesenteric plexus and enter the spinal cord at the T10 level to produce vague, referred pain at the umbilicus (Choice C). As the appendix becomes more inflamed, it irritates the parietal peritoneum and abdominal wall and causes a more severe somatic pain that shifts from the umbilical region to the McBurney point (two-thirds of the distance from the umbilicus to the anterior superior iliac spine). With peritoneal irritation, the abdominal wall becomes very sensitive to gentle palpation or sudden release of pressure (ie, rebound tenderness). The appendix is usually located 2 cm beneath the ileocecal valve in the right lower quadrant. Depending on its orientation, there can be additional clinical findings. A pelvic appendix lies against the right obturator internus muscle, causing right lower quadrant pain with internal rotation of the right hip (Choice A). Patients with a retrocecal appendix may not have significant right lower quadrant tenderness because the inflamed appendix does not contact the anterior parietal peritoneum, and the cecum (distended with gas) acts as a cushion that blocks the examiner's hand. However, the inflamed appendix will lie against the right psoas muscle, causing pain with hip extension (Choices B and E). Educational objective: Appendicitis causes dull visceral pain at the umbilicus due to afferent pain fibers entering at the T10 level in the spinal cord. Progressive inflammation in the appendix irritates the parietal peritoneum and abdominal wall to cause more severe somatic pain shifting from the umbilicus to McBurney's point (two-thirds of the distance from the umbilicus to the anterior superior iliac spine).

A 21-Year-Old Man Comes to the Emergency Department Due to Abdominal