Abdominal Pain
Perspective
Epidemiology
Abdominal pain accounts for up to 10% of all ED visits. Some of the most common causes of acute abdominal pain are listed in Table 27-1. Many patients have pain and other symptoms that are not typical of any specific disease process. Even after ED workup, a diagnosis may not be found in some patients. In addition, several adult groups deserve special consideration: elders (those older than 65 years of age), the immunocompromised, and women of reproductive age.
Table 27-1
Increasingly, emergency physicians are seeing patients in immunocompromised states secondary to human immunodeficiency virus and acquired immunodeficiency syndrome (HIV/AIDS), uncontrolled diabetes, chronic liver disease, chemotherapy, and immunosuppressive drugs. For many reasons, these patients also prove challenging. Their clinical presentation can be misleading owing to atypical physical and laboratory findings, such as lack of fever. The white blood cell (WBC) count, which is unreliable in all cases of abdominal pain, may be frankly misleading in such patients, such as in those with persistent elevations. With regard to infection, the scope of the differential diagnosis also should be broader than usual.1,2 Presentations in the immunocompromised patient may be highly variable and subtle and are discussed in Chapter 183.
Pathophysiology
Pathology in the gastrointestinal and genitourinary tracts remains the most common source of pain perceived in the abdomen. Also, pain can arise from a multitude of other intra-abdominal and extra-abdominal locations (Box 27-1). Abdominal pain is derived from one or more of three distinct pain pathways: visceral, somatic, and referred.
• Foregut structures (stomach, duodenum, liver, and pancreas) are associated with upper abdominal pain.
• Midgut derivatives (small bowel, proximal colon, and appendix) are associated with periumbilical pain.
• Hindgut structures (distal colon and genitourinary tract) are associated with lower abdominal pain.
Somatic pain occurs with irritation of the parietal peritoneum. This is usually caused by infection, chemical irritation, or another inflammatory process. Sensations are conducted by the peripheral nerves and are better localized than the visceral pain component. Figure 27-1 illustrates some more typical pain locations corresponding to specific disease entities. Somatic pain is often described as intense and constant. As disease processes evolve to peritoneal irritation with inflammation, better localization of the pain to the area of pathology generally occurs.
Referred pain is defined as pain felt at a distance from its source because peripheral afferent nerve fibers from many internal organs enter the spinal cord through nerve roots that also carry nociceptive fibers from other locations, as illustrated in Figure 27-2. This makes interpretation of the location of noxious stimuli difficult for the brain. Both visceral pain and somatic pain can manifest as referred pain. Two examples of referred pain are the epigastric pain associated with an inferior myocardial infarction and the shoulder pain associated with blood in the peritoneal cavity irritating the diaphragm. It is common for a patient to interpret pain originating from the hips as pelvic pain, especially in the very young or elderly. Lower lobe pneumonias can cause referred abdominal pain secondary to diaphragmatic irritation. Finally, some metabolic disorders and toxidromes may manifest with abdominal pain.
Diagnostic Approach
Differential Considerations
Although significant morbidity and mortality can result from many disorders causing abdominal pain, a few processes warrant careful consideration in the ED. Table 27-2 lists important potentially life-threatening nontraumatic causes of abdominal pain. This group represents the major causative disorders likely to be associated with hemodynamic compromise and for which early therapeutic intervention is critical.