The two sets of diagnoses that I encounter most frequently with this problem are Mesenteric Ischemia (or Ischemic Bowel) and Ischemic Colitis and Aortic Dissection and Aortic Aneurysm (often manifested in the unlikely "dissecting aneurysm").
Mesenteric Ischemia: Dead bowel (small or large) usually cause by a vascular thrombus (arterial versus venous) classically leading to abdominal pain out of proportion to the physical exam and lactic acidosis. The diagnosis is confirmed by angiography or in the operating room and the treatment is almost always surgical.
Ischemic Colitis on the other hand is a shedding of the endothelial lining of the intestines (large versus small) affecting watershed areas. The cause is a low flow state such as the hypotension and hypo-perfusion seen in sepsis and heart failure. Usually there is no vascular lesion. The patient exhibits diarrhea (sometimes bloody) and abdominal pain. Treatment is not usually surgical, rather aimed at improving the hemodynamics.
Aortic Dissection is caused by a tear in the intimal layer of the aorta. Blood dissects creating a false lumen and clot. Symptoms are chest pain, neurovascular catastrophes and ischemia, cardiac tamponade and valvular emergencies. Mainstay of treatment is blood pressure and heart rate control, and a subset of these are managed operatively.
Aortic Aneurysm on the other hand, is a dilatation of the abdominal aorta that has an increased risk of rupture as the size increases. Surgical and endovascular repair are options while the patient is stable, but when these aneurysms are known to be ruptured or rupturing the emergency surgery and blood transfusions (as opposed to antihypertensives) are the indicated treatments.
Have you encountered colleagues and learners who mix these up too? How do you keep them apart or teach others about these differences?
Can you think of other diseases or diagnoses that present similar cognitive problems?