What is the most appropriate initial investigation for a female patient with a history of crampy abdominal pain radiating to the back and watery diarrhea for 1 year?

Appropriate Investigation for Female with Chronic Abdominal Pain and Diarrhea

Pelvic and abdominal ultrasound (US) is the most appropriate initial investigation for a female patient with a one-year history of crampy abdominal pain radiating to the back and watery diarrhea.

Diagnostic Approach Rationale

The clinical presentation suggests irritable bowel syndrome (IBS) or other chronic gastrointestinal conditions, but structural causes must be ruled out first. The diagnostic approach should follow these principles:

Initial Imaging Selection

• Ultrasound is recommended as the first-line imaging modality for several reasons:
  • According to ACR Appropriateness Criteria, US is appropriate for initial evaluation of abdominal pain, especially when gynecologic causes are in the differential 1
  • US avoids radiation exposure while providing visualization of abdominal and pelvic organs
  • US can identify common causes of abdominal pain including gallbladder disease, ovarian cysts, fibroids, and other pelvic pathology 1
  • The chronic nature (1 year duration) makes acute surgical emergencies less likely

Why Not Amylase or Lipase First?

• Amylase and lipase are specific tests for pancreatic disease, particularly acute pancreatitis
• The clinical presentation (chronic symptoms for 1 year with watery diarrhea) is not typical for acute pancreatitis
• According to guidelines, amylase and lipase are most useful for acute onset of severe supraumbilical pain, not chronic symptoms 2
• Laboratory tests including amylase would be appropriate if the US shows pancreatic abnormalities or if symptoms were acute rather than chronic

Diagnostic Algorithm

1. First step: Pelvic and abdominal US

   • Evaluates for structural abnormalities in both abdomen and pelvis
   • Can identify gynecologic causes (ovarian cysts, fibroids) 1
   • Can detect gallbladder disease, which can present with similar symptoms
   • Can visualize the pancreas and detect gross abnormalities

2. If US is normal or inconclusive:

   • Laboratory tests including CBC, comprehensive metabolic panel, and stool studies
   • Consider testing for IBS or other functional bowel disorders 1
   • The American Gastroenterological Association recommends screening with stool Hemoccult and CBC for patients with suspected IBS 1

3. If US shows abnormalities or symptoms persist:

   • CT abdomen/pelvis with contrast may be indicated
   • ACR guidelines note CT has higher sensitivity (89% vs 70%) than US for urgent diagnoses in adults with abdominopelvic pain 1
   • Consider colonoscopy, especially for patients over 50 or with alarm symptoms

Important Considerations

• The chronic nature (1 year) of symptoms makes functional disorders like IBS more likely than acute conditions
• The American Gastroenterological Association notes that IBS diagnosis requires exclusion of structural causes 1
• Radiographic studies should be tailored to the clinical presentation and suspected diagnosis
• While CT has higher overall sensitivity, US is appropriate as the first-line imaging study for this presentation due to lack of radiation and ability to evaluate both abdominal and pelvic structures

In conclusion, pelvic and abdominal ultrasound is the most appropriate initial investigation for this patient's presentation, with further testing guided by these results.