Today we discussed a case of subacute, progressive lower abdominal pain which turned out to be small bowel involvement of amyloidosis. The differentiation of acute or subacute/chronic abdominal pain is difficult to tease out, as there is no clear, binary transition point when pain becomes "chronic" from "acute." What seems to be the most helpful is differentiating those with an urgent problem from those without, and subsequently determining the quadrant of interest in those with nonurgent pain.
RUQ Pain: These are, in general, hepatobiliary problems. Hepatic pain results when the liver capsule is stretched from edema or otherwise. By and large, these are predominantly biliary sources of pain. Lab and imaging should be focused on the hepatobiliary tree. An ultrasound could be obtained to evaluate for appropriate sources as well.
Epigastric Pain: Once angina is ruled out as a cause, one would consider pancreatic and gastric causes of pain. Hepatobiliary pain can also refer to the epigastrium. Dyspepsia is a rule out differential for pain, but can be diagnosed when limited to the epigastrium and associated with other common symptoms (bloating, abdominal fullness, heartburn, nausea).
LUQ Pain: Rare. Most often due to splenic abnormalities. Imaging could include ultrasound or CT.
Lower Abdominal Pain: Usually associated with the distal intestinal tract (diverticulitis, colitis, colorectal cancer, constipation) down from other structures. The key here is to check a pregnancy test in women of childbearing age. Other systems that can be tricky would be the GU tract.
Diffuse Pain: Can be primarily from etiologies that cause diffuse pain (obstruction, ischemia, gastroenteritis, IBS, food intolerance), or from focal etiologies that have progressed. Also to consider are pulmonary etiologies that have referred, again a pregnancy, DKA, adrenal insufficiency, electrolyte abnormalities such as hypercalcemia.