Differential Diagnosis for Daily Nausea and Pain in Lower Right Abdomen

Given the symptoms of daily nausea and pain in the lower right abdomen most days after eating, with no gallstones, no celiac disease, and clear endoscopy and abdominal ultrasound (all four quadrants), the differential diagnosis can be broken down into the following categories:

• Single Most Likely Diagnosis (40%):

  • Irritable Bowel Syndrome (IBS): This condition is characterized by chronic abdominal pain, bloating, and alteration of bowel habits in the absence of any mechanical, inflammatory, or biochemical abnormalities. The symptoms can be exacerbated by eating and can fit the patient's presentation, especially given the absence of other findings.

• Other Likely Diagnoses (40%):

  • Inflammatory Bowel Disease (IBD): Although the endoscopy was clear, IBD (including Crohn's disease and ulcerative colitis) can sometimes present with subtle or patchy inflammation that might not be detected on a single endoscopy. The symptoms of abdominal pain and nausea, especially after eating, could be consistent with IBD.
  • Functional Dyspepsia: This condition involves persistent or recurrent upper abdominal pain or discomfort that is not exclusively relieved by defecation or associated with the onset of a bowel movement. It could contribute to nausea and might be exacerbated by eating.
  • Gastroesophageal Reflux Disease (GERD): Although typically associated with heartburn, GERD can also cause nausea and abdominal pain, especially after eating.

• Do Not Miss Diagnoses (15%):

  • Appendicitis: Although the pain is described as being in the lower right abdomen, which is consistent with appendicitis, the fact that it occurs most days after eating and has been ongoing suggests this is less likely. However, appendicitis can present atypically, and missing this diagnosis could be catastrophic.
  • Ovarian Cysts or Torsion: In female patients, ovarian cysts or torsion could cause lower abdominal pain and nausea. These conditions require urgent attention.
  • Intestinal Obstruction: This is a less likely but critical diagnosis to consider, as it can cause severe abdominal pain, nausea, and vomiting. The absence of clear findings on ultrasound does not entirely rule out a partial or intermittent obstruction.

• Rare Diagnoses (5%):

  • Chronic Intestinal Pseudo-obstruction: A rare condition characterized by the presence of symptoms of intestinal obstruction without any physical blockage.
  • Eosinophilic Gastroenteritis: A rare inflammatory condition of the gastrointestinal tract that can cause abdominal pain, nausea, and vomiting.
  • Abdominal Migraine: A condition that can cause recurrent episodes of severe abdominal pain, often accompanied by other symptoms like nausea and vomiting, in the absence of any clear organic cause.

Each of these diagnoses has a brief justification based on the symptoms and test results provided. The percentages are approximate and based on the likelihood of each condition given the clinical presentation and the results of the investigations mentioned.