Thursday, February 4, 2010
February 2nd - MHH - Mesenteric Ischemia and Ischemic Bowel Disorders
Housestaff frequently interchange the different ischemic diseases of the bowel, and I've hear the term "ischemic colitis" to describe the clinical scenario above. Here is a review of the different ischemic disorders involving the bowel.
There are essentially 4 ischemic disease that affects the mesentery - acute and chronic mesenteric ischemia, mesenteric thrombosis and ischemic colitis. Keep in mind, that each of these has a variety of causes (see below).
In almost all of the causes, the presentation is similar - post prandial abdominal pain, weight loss and "fear of eating." Most of these symptoms occur indolently, yet depending on the cause, this symptoms can present more acutely. The symptoms simply occur from a supply/demand mismatch, and the SMA is the usual site of involvement. Overall, these patients DO NOT present with blood in the stool/diarrhea.... that is unless there is another overlapping cause that leads to gut infarction. This overlapping cause is usually caused by severe hypovolemia, cardiogenic shock or sepsis.
On exam, the classic presentation is that the patient's complaint of pain is out of proportion to the exam. In fact, the way that patients describe pain - one may suspect that they would have peritoneal signs, but they are essentially non-tender during the exam. (Remember, however, that this would not be the case if there was gut infarction that resulted from an overlapping cause). In all patients, Auscultation of the abdomen may reveal a bruit.
Acute Mesenteric Ischemia - These patients usually present acutely, and are the highest risk of developing infarction of the bowel. There are a variety of causes, but in all - patients have poor perfusion of the colon - usually at the area of the SMA
Embolic Disease: Common causes of this include atrial fibrillation, or a mural clot post myocardial infarction.This is sometimes seen after vascular surgery as well. Emesis is usually present.
Mesenteric Arterial Thrombosis: Usually causes by rupture of an atherosclerotic plaque. Patients present usually when precipitated by low-flow states. These cases commonly develop gut infarction/necrosis rapidly.
Non-occlusive disease: Hypotension from a variety of causes (MI, Sepsis, etc), vasopressors, cocaine and Digoxin
Workup of Acute Mesenteric Ischemia: CBC (may have elevated white count, and usually hemoconcentration occurs), Amylase usually elevaed. Can have a lactic acidosis. KUB (to rule out other causes) may have findings later in the disease course (especially c/w SBO). CT may be helpful, but mostly to rule out other causes of abdominal pain. Diagnosis is usually done via angiography, which is currently preferred over MRA.
Treatment of Acute Mesenteric Ischemia: This is an emergency, as it can rapidly progress to bowel infarction and gangrene During angiography, thrombolytics can use used with ischemic disease. Some may need angioplasty or stents afterwards if there is atherosclerotic disease. Less emergent cases can be treated with Heparin or LMWH. If there are any signs of infarction (peritonitis, acidosis, lactic acid up) - then emergent surgery is needed
Chronic Mesenteric Ischemia - Over 90% of patients with this have atherosclerotic disease as the cause. They usually have more chronic symptoms, and although they rarely get gut infarction, they have a high risk of emboli/thrombosis which can lead to infarction. Think of this as the cause of abdominal pain in a patient with risk factors for coronary artery disease (esp Smoking, DM, HTN, Dyslipidemia) and/or have a history of CAD/MI/CVA/PVD.
Workup of Chronic Mesenteric Ischemia: Mostly done to rule out other causes (i.e. liver disease, pancreatitis, biliary disease, nephrolithiasis, etc). Angiography is the gold standard for diagnosis.
Treament of Chronic Mesenteric Ischemia: Stenting of the SMA. If this is not possible, endarterectomy or bypass can be performed
Mesenteric Venous Thrombosis - Usually presents acutely, but can be chronic. Causes by other things you would think of causing venous thrombosis - hypercoaguable states (esp Factor V Leidin, Protein C/S, PNH), pancreatitis, cirrhosis and sickle cell disease.
Patients present very similarly to those with mesenteric ischemia - post-prandial abdominal pain, "fear of food" and weight loss. The exam is the same as well - essentially non-tender although the patient complains of a lot of pain. Bruits are not usually heard.
Workup: Rule out other causes of abdominal pain. CT scan is the test of choice. Once imaging shows findings c/w a thrombosis - then workup the cause.
Treatment: Consists of heparin/LMWH then long-term coumading. Thrombolysis for emergent cases. Surgery is signs of infarction/peritonitis develop.
Ischemic Colitis (aka Colonic Ischemia - confusing huh?)
These Patients have a non-occlusive cause of their disease. Unlike the above causes, which invariably affect the SMA, this disease usually affects the IMA. Especially involved is the so called "watershed area" of the splenic flexure. Any area distal from the splenic flexure, however, can be involved.
There are multiple causes of this - mostly post-operative, low-flow states, hypercoaguable states, vasospastic drugs (cocaine), vasculitis and history of radiation exposure. Embolism post MI or from Afib is RARELY the cause.