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PATIENT 
Mr. L is a 65-year-old man who arrives in the emergency department complaining of 1 hour of excruciating constant diffuse periumbilical abdominal pain radiating to his left flank. He has never had pain like this before. He has suffered 1 episode of vomiting and feels light headed. The emesis was yellow. He has moved his bowels once this morning and continues to pass flatus. There is no change in his bowel habits, melena, or hematochezia. Nothing seems to make the pain better or worse. He was without any pain until this morning. His past medical history is remarkable for hypertension and tobacco use and appendectomy at age 12. On physical exam, he is diaphoretic and in obvious acute distress. Vital signs are BP, 110/65 mm Hg; pulse, 90 bpm; temperature, 37.0°C; RR, 20 breaths per minute. HEENT, cardiac, and pulmonary exams are all within normal limits. Abdominal exam reveals moderate diffuse tenderness, without rebound or guarding. Bowel sounds are present and hypoactive. Stool is guaiac negative.
At this point, what is the leading hypothesis, what are the active alternatives, and is there a must not miss diagnosis? Given this differential diagnosis, what tests should be ordered?
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RANKING THE DIFFERENTIAL DIAGNOSIS
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Mr. L has severe, diffuse, and acute abdominal pain. The first pivotal point evaluates the location of the pain. Mr. L’s pain is diffuse, which limits the differential diagnosis. Common causes of diffuse mid abdominal pain include IBS; IBD; SBO or LBO; acute ischemia; AAA; diabetic ketoacidosis; gastroenteritis; and, given the radiation of pain to his back, pancreatitis, and nephrolithiasis (Figure 3-1). Although this is an extensive differential, it can be focused further. Several of these diagnoses are very unlikely and need not be considered further. Given the lack of diarrhea and the severity of pain, gastroenteritis is very unlikely. His continued bowel movements and flatus make bowel obstruction unlikely (although this can be seen early in obstruction.) The lack of a history of diabetes would make diabetic ketoacidosis unlikely, unless this was the initial presentation; a simple blood sugar could help exclude this diagnosis. The second pivotal point which can serve to narrow the differential diagnosis is the time course of the pain, which is hyperacute. Of the remaining hypotheses, AAA, bowel ischemia, pancreatitis, and nephrolithiasis can all present acutely, whereas this would be very unlikely presentation of IBD or IBS. The radiation to the left flank increases the likelihood of AAA, nephrolithiasis, and pancreatitis. Clearly, AAA is a must not miss diagnosis. Other pivotal findings that can help narrow the differential diagnosis include peritoneal findings on exam, unexplained hypotension and abdominal distention. Table 3-14 lists the differential diagnoses for Mr. L.
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