Differential Diagnosis Series – Abdominal Pain (Part 2)

This post is the second of two detailing the construction of a differential diagnosis for abdominal pain.  The post yesterday consisted of a review of the relevant history and physical exam for abdominal pain patients.  This article is also posted at my site:  510medic.com

COMMON EMS DIAGNOSES
While many causes for abdominal pain require lab work and diagnostic studies in the hospital environment, there are some common or potentially life-threatening diagnoses that are considering “can’t miss” in the prehospital setting.

APPENDICITIS
Appendicitis, as the name might suggest, is inflammation of the appendix.  Caused by blockage of the entrance of the appendix, the organ swells, eventually bursting and filling the abdominal cavity with infectious material.  The result of an abdominal infection is peritonitis, another life threatening condition.  Traditionally, there are several signs that have been taught to EMS responders to determine if a patient has a probable appendicitis:  fever, rebound, guarding and tenderness over McBurney’s point.  As it turns out, fever is neither sensitive (15-67%), nor highly specific (85%) for appendicitis (1).  As a refresher, this sensitivity means that 15-67% of abdominal pain patients with no fever (a negative finding) will not have an appendicitis.  Needless to say, this number does not inspire a lot of confidence in ruling out appendicitis.  Conversely, 85% of patients with an appendicitis will have a fever (1).  McBurney’s point (halfway along a line drawn from the umbilicus to the iliac crest) is no better,  Tenderness over that point is present in only 50% of appendicitis patients.  Lastly, rebound has a sensitivity of 61% and a specificity of 82% and guarding has a sensitivity of 46% and a specificity of 92% (1).  So what this all means is that a patient with abdominal pain and all of the following symptoms:  fever, pain over McBurney’s point, guarding and rebound tenderness likely has an appendicitis.  What this also means is that a patient can have abdominal pain and none of the other symptoms and still have an appendicitis.

ECTOPIC PREGNANCY
An ectopic pregnancy occurs when an embryo implants somewhere other than the uterus.  Most often, this implantation occurs in the fallopian tube and can cause a rupture as the pregnancy progresses.  This obviously represents a significant threat to the life of the mother.  As ruptured ectopic is the leading cause of pregnancy-related death during the first trimester (2), it is important to keep a high index of suspicion, since a patient may not yet know she is pregnant.  To this end, any female patient of child-bearing age presenting with abdominal pain, syncope, hypotension or vaginal bleeding should be considered for a possible ruptured ectopic.  Pain from a ruptured ectopic pregnancy will typically present in the right or left lower quadrant (depending on which side the pregnancy implanted) and may present with profound hypotension.  Ultimately, clinical findings cannot effectively  rule out ectopic pregnancy and an in-hospital ultrasound is needed (2).

PANCREATITIS
Pancreatitis is inflammation of the pancreas occurring in either chronic or acute forms.  Chronic pancreatitis can result from alcohol and illicit drug abuse and, as such, is more often seen in the prehospital setting.  Most of the actual diagnostic work for pancreatitis takes place in the in-hospital setting.  Lab values are particularly helpful including pancreatic function tests and, of course, the ever-present abdominal CT (1).  In the prehospital setting, most of the leg work goes towards history-taking.  Patients with epigastric pain, often radiating to the back, with associated nausea and vomiting and a history of chronic alcohol abuse who have been ruled out for cardiac and respiratory causes should be considered for pancreatitis (1).  Additionally, a history of pancreatitis diagnosis and a comparison of the presenting symptoms to the historical symptoms is helpful.

BOWEL OBSTRUCTION
As the name indicates, this condition occurs when something obstructs the passage of fecal matter through the bowels.  This condition can result from chronic constipation, foreign object, or conditions like cancer or polyps.  Over half of the cases of large bowel obstruction result from the presence of cancer (1).  Patients generally present with episodes of increased pain during which bowel sounds are notably louder (even audible without a stethoscope).  The patient may present with abdominal distention (89% specific), previous abdominal surgery (94% specific) and constipation (95% specific) (1).  While these findings are fairly specific (positive findings rule in large bowel obstruction), they are relatively insensitive (a negative finding does not reliably rule out large bowel obstruction).  Making up 80% of bowel obstruction cases, small bowel obstruction is most often caused by post-operative adhesions (70%) (1).  For the purposes of the prehospital community, large and small bowel obstruction present with essentially the same findings in the history and exam.  Field treatment of bowel obstruction includes fluid resuscitation and pain management.

MESENTERIC ISCHEMIA
The small intestine is supplied with blood and nutrients by the mesenteric artery.  When this artery does not provide adequate circulation, ischemia of the small bowel can result.  While it can be caused by hypotension from hemorrhage in trauma (resulting in the “golden hour” – but that’s another post), the disease process here results from a clot blocking blood flow.  Other than abdominal pain, there are not many physical findings in EMS which can aid in a differential diagnosis of mesenteric ischemia.  If advanced, ischemia may result in decreased bowel sounds.  Often, patients will complain of pain much more severe than their physical finding would indicate (1).  A thorough history will serve the practitioner in this diagnosis.  Patients at high risk for clotting (history of atrial fibrillation, CHF, bed confinement, and recent surgical procedures) should be considered high risk for mesenteric ischemia (1).  Since the presence of mesenteric ischemia can be so life threatening, rapid transport should be considered if this disease process is considered likely.

CHOLECYSTITIS
Hopefully by this point we’re all on board with “-itis” meaning inflammation.  In this case we’re talking about the gall bladder and inflammation and pain specific to it.  The inflammation in question generally results from a prolonged blockage of the common bile duct, often resulting from gall stones.  The pain from cholecystitis is found in the right upper quadrant 54% of the time and in the epigastric region 34% of the time.  The pain generally comes and goes and is often cramping in nature,  radiating to the back, flank and chest (1).  For this reason, it is important to determine where the pain started before radiating and also to perform a 12 lead ECG for abdominal pain patients.

ABDOMINAL AORTIC ANEURYSM
An aneurysm is an out-pouching from an artery caused by a weakening of the arterial wall (see my post about CVA for some images of a cerebral aneurysm; same idea, different location).  In the abdomen, pain can be caused by an aneurysm of the abdominal aorta, a life-threatening condition requiring rapid assessment and treatment.  It is important to note that ultimately, the physical exam cannot totally rule out AAA from consideration.  One of the most important findings in the patient examination for ruling in AAA is orthostatic vital signs.  Since the patient often will not have large quantities of emesis or diarrhea, dehydration is ruled out as a cause of abnormal vital signs. A history of GI bleed symptoms (or lack thereof) will rule in or out that diagnosis as well. The classic presentation of AAA is historical hypertension, presenting with constant, severe abdominal pain, pulsating mass in the abdomen and profoundly positive orthostatic vital signs.  It is important to note, however, that for symptomatic AAA, a palpable mass is only present in 18% of patients (1).  For a ruptured AAA, the treatment is surgical.  Think of this as a trauma patient; the speed with which a patient can bleed out is staggering.  In this case, C3 transport is obviously indicated.

CONCLUSION
Abdominal pain is a frequent call for many EMS responders.  Given the breadth of possible causes, it is important for practitioners to keep a high index of suspicion for life-threatening causes.  Performing a thorough physical exam and history on patients with abdominal pain (even chronic ones!) will help to ensure that “must catch” diagnoses are caught.  Do your patients a favor and make sure that you give them the benefit of the doubt, particularly with a complaint as complex as abdominal pain.

CITATIONS

1 – Stern, Scott; Cifu, Adam; Altkorn, Diane. Symptom to Diagnosis:  An Evidence-Based Guide. New York:  Lange Medical Books, 2006.

2 – Lozeau, Anne-Marie; Potter, Beth. Diagnosis and Management of Ectopic Pregnancy. Am Fam Physician. 2005. 72(9): 1707-14.