Most cases of abdominal pain do not result from a life-threatening condition. When they do, they may not differ obviously from cases in which the cause of pain is benign.
As many as half of patients who are evaluated for abdominal pain do not receive a precise diagnosis. And for about half of those who are given a diagnosis, the diagnosis is wrong.1,2 Misdiagnosis can divert attention from a serious disorder or lead to ill effects of unnecessary treatment.
In this article, I will use actual cases (not "textbook" examples) to illustrate an approach to abdominal pain that begins with a careful differential diagnosis. I also offer some general guidelines for evaluating patients (Box I).
ELDERLY WOMAN WITH NAUSEA AND VOMITING
Initial evaluation. An 84-year-old woman presented with a 2-day history of nausea, vomiting, and constant lower abdominal pain; she had no anorexia, hematemesis, diarrhea, constipation, or urinary tract symptoms. She had no significant medical conditions or allergies and was taking no medications.
Heart rate was 97 beats per minute; blood pressure, 94/60 mm Hg; respiration rate, 18 breaths per minute; temperature, 37.6°C (99.7°F); and oxygen saturation, 95% on room air. Head and neck, cardiac, and pulmonary examination results were normal. The patient exhibited bilateral lower abdominal tenderness with rebound tenderness and guarding. The remainder of the examination revealed no abnormalities.
Differential diagnosis in elderly patients. Abdominal pain in the elderly is a medical Pandora's box. Of patients 65 years or older who present to the hospital with abdominal pain, about 7% die and 22% to 40% need surgery. Furthermore, the cause of the pain remains unknown almost twice as frequently in elderly as in younger patients.3
Always keep in mind the dangerous triad of vascular catastrophes that can cause abdominal pain, especially in older patients:
- Abdominal aortic aneurysm (AAA).
- Mesenteric ischemia.
- Myocardial infarction.
In this case, we can exclude myocardial infarction, since the patient had lower abdominal pain only, with rebound tenderness and guarding confined to that area. Generally, however, when a patient older than 50 years presents with diffuse abdominal or upper abdominal pain, consider an acute coronary syndrome. If another plausible explanation for the pain is not apparent, admission and cardiac workup are usually warranted.
We must still consider the other 2 components of the dangerous triad--AAA and mesenteric ischemia--as well as more common serious pathologies. A reasonable differential diagnosis for this patient includes:
- Atypical acute cholecystitis with gangrene.
- Mesenteric ischemia.
- Perforated viscus.
The next steps. Blood test results were normal, including a white blood cell (WBC) count of 9000/µL. Urinalysis showed 16 WBCs per high-power field (hpf), 7 red blood cells (RBCs) per hpf, and a few epithelial cells. Findings on abdominal films were normal.
The abnormal urinalysis results and normal WBC count and temperature were consistent with a urinary tract infection. However, the abdominal tenderness required further evaluation. A helical CT scan suggested perforating appendicitis (Figure 1). Surgical exploration revealed acute suppurative appendicitis with rupture.
Had the results of abdominal CT been normal, it would have been necessary to evaluate this patient for mesenteric ischemia. Although routine multidetector CT (MDCT) may yield positive findings in about 80% of cases of mesenteric ischemia, it cannot reliably exclude the diagnosis.4 No combination of laboratory tests can rule out this deadly condition. Only laparotomy and conventional mesenteric angiography or, in some centers, a dedicated MDCT mesenteric angiogram can do so.5 One of these procedures should be performed when mesenteric ischemia is suspected after a nondiagnostic initial workup.
Appendicitis. About 7% of the population has had an episode of appendicitis.6 The cause is obstruction of the appendiceal lumen by fecal matter. As secreted fluids accumulate, distention of the appendix leads to ischemic necrosis and bacterial infection of the devitalized tissue. Appendicitis is generally well tolerated by young, otherwise healthy patients. For elderly or immunocompromised patients, however, the associated morbidity and mortality are much higher.
The diagnostic sensitivity and specificity of various clinical signs and symptoms of appendicitis have been well studied (Table 1).7 No single finding is reliable in isolation; diagnosis based on the history and physical examination remains an "art." The presentation of appendicitis is often atypical in elderly patients, who display fever, rebound tenderness, and guarding in fewer than 50% of cases. Furthermore, 20% to 30% of patients with appendicitis have symptoms or urinalysis findings that may suggest urinary tract infection.8 Presumably, inflammation of the appendix induces a sterile pyuria in the adjacent ureter, a condition that may also accompany diverticulitis.
Although universally obtained when appendicitis is suspected, laboratory studies are often unhelpful and can be misleading. The WBC count has an overall sensitivity of about 80% and a much lower specificity. It is more likely to be normal early in the course of the disease; in immunocompromised persons; or at the extremes of age, when the presentation of appendicitis tends to be more obscure. The C-reactive protein assay does little to enhance the accuracy of the WBC count. I do not recommend routine use of the assay for the diagnosis of appendicitis.9
Can imaging studies improve the diagnosis of appendicitis? Ultrasonography results may be helpful if positive, but negative results do not exclude appendicitis. Its sensitivity was summarized in a recent systematic review and ranges from 38% to 82%.10 Ultrasonography may be a preferred first step in gravid patients or in children who lack the visceral fat needed to identify inflammation adjacent to the appendix on CT.11 Ultrasound scanning may also detect other diseases that are important in the differential diagnosis of appendicitis, especially pelvic disorders in female patients. However, it is highly operator- and patient-dependent, which limits its usefulness in most centers.
Helical CT scanning is the best imaging test for most patients. In expert hands, helical CT is highly sensitive (96% to 100%). The sensitivity of 100% obtained by Rao and coworkers12-14 required the use of colonic contrast material. If only intravenous or oral contrast material is used, the sensitivity may be somewhat lower, although it probably still ranges from 90% to 95%.15,16
Helical CT is also useful in diagnosing other abdominal abnormalities that are included in the differential diagnosis, such as AAA, diverticulitis, nephrolithiasis, cholelithiasis, colon cancer, and gynecologic disorders. Unlike ultrasonography, helical CT can rule out appendicitis by showing a nondistended appendix that fills with contrast material.
When the clinical evidence of appendicitis is obvious, the diagnosis can be made on the basis of the history and physical examination alone and the patient can proceed to surgery. When the diagnosis is in question, helical CT is the imaging test of choice in most cases.
LESSONS FROM THIS CASE
- Imaging studies are most helpful in diagnosing appendicitis in patients who tend to exhibit less clear-cut presentations of the disease, including the very old, the very young, and those with comorbidities.
- When you suspect appendicitis or diverticulitis, do not be dissuaded from further investigation by findings that suggest urinary tract infection.