Differential Diagnosis for Abdominal Symptoms

Given the information that colonoscopy and calprotectin tests have been conducted, we can approach the differential diagnosis for the symptoms presented, which seem to be related to bowel habits and abdominal discomfort, potentially pointing towards Irritable Bowel Syndrome (IBS) but also considering other possibilities.

• Single Most Likely Diagnosis

  • Post-Infectious IBS (PI-IBS): This condition is a subtype of IBS that occurs after an episode of acute gastroenteritis. The sudden onset of symptoms, as mentioned, aligns more closely with PI-IBS than classic IBS, which typically has a more gradual onset.

• Other Likely Diagnoses

  • Classic IBS: Although less likely due to the sudden onset, classic IBS remains a possibility, especially if stress or other triggers have recently changed. However, the absence of a gradual onset and the negative findings from diagnostic tests like colonoscopy and calprotectin make this less probable.
  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis could present with similar symptoms. However, the calprotectin test, which is often elevated in IBD, has been checked, suggesting this might be less likely, though not entirely ruled out without further testing or biopsy results.

• Do Not Miss Diagnoses

  • Colorectal Cancer: Although less common in younger individuals, colorectal cancer can present with changes in bowel habits, abdominal pain, and other non-specific symptoms. The fact that a colonoscopy has been performed significantly reduces the likelihood but does not entirely rule out the possibility of a missed lesion or other gastrointestinal malignancies.
  • Gastrointestinal Infections: Certain infections (bacterial, viral, or parasitic) can cause persistent gastrointestinal symptoms. The history of sudden onset and negative calprotectin test might suggest an infection, but this would typically be accompanied by other symptoms like fever, weight loss, or specific dietary intolerances.
  • Celiac Disease: An autoimmune reaction to gluten, leading to small intestine damage, can cause abdominal pain, diarrhea, and other symptoms similar to IBS. This condition is important not to miss due to its potential for long-term complications if left untreated.

• Rare Diagnoses

  • Microscopic Colitis: A condition characterized by inflammation of the colon lining that can only be diagnosed through biopsy. It presents with chronic, watery diarrhea and can be a consideration in patients with negative colonoscopy findings but persistent symptoms.
  • Bile Acid Diarrhea: A condition where the body produces too much bile acid, leading to chronic diarrhea. This is a less common cause of chronic diarrhea but should be considered in the differential diagnosis, especially if other causes have been ruled out.