Differential Diagnosis

The patient presents with a history of episodes of abdominal pain, unintentional weight loss, and fever, along with findings of uniform inflammation in the colon from the distal rectum to the mid-transverse colon on colonoscopy. The following differential diagnoses are considered:

• Single Most Likely Diagnosis

  • Ulcerative Colitis (UC): This is the most likely diagnosis given the patient's symptoms of abdominal pain, weight loss, fever, and the colonoscopy findings of uniform inflammation starting from the distal rectum and extending to the mid-transverse colon. UC is a type of inflammatory bowel disease (IBD) characterized by chronic inflammation and ulceration of the colon's inner lining, typically starting in the rectum and extending proximally in a continuous manner.

• Other Likely Diagnoses

  • Crohn's Disease: Although less likely than UC due to the pattern of inflammation, Crohn's disease is another type of IBD that can present with similar symptoms. It can affect any part of the gastrointestinal tract, from the mouth to the anus, and the inflammation can be patchy.
  • Infectious Colitis: This could be considered, especially given the fever and weight loss. However, the uniform inflammation pattern and the absence of a clear infectious agent make this less likely.
  • Diverticulitis: Given the tenderness in the left lower quadrant, diverticulitis could be a consideration, but the colonoscopy findings and the pattern of symptoms are not typical for diverticulitis.

• Do Not Miss Diagnoses

  • Colon Cancer: Although less likely in a relatively young patient, unintentional weight loss and changes in bowel habits can be symptoms of colon cancer. The presence of inflammation could potentially mask or be associated with a malignancy.
  • Invasive Infectious Diseases (e.g., Tuberculosis, Amoebiasis): These conditions can mimic IBD and must be considered, especially if the patient has risk factors for exposure or if the response to standard IBD treatment is poor.
  • Ischemic Colitis: This condition can present with abdominal pain and weight loss, and while it's less likely given the uniform inflammation pattern, it's a critical diagnosis not to miss due to its potential for severe complications.

• Rare Diagnoses

  • Microscopic Colitis: This condition involves inflammation of the colon that can only be seen with a microscope. It can cause chronic diarrhea and weight loss but typically does not cause the fever and significant abdominal pain seen in this patient.
  • Eosinophilic Colitis: A rare condition characterized by eosinophilic infiltration of the colonic mucosa, which can present with abdominal pain, diarrhea, and weight loss. It is less common and would be considered if other diagnoses are ruled out.
  • Behçet's Disease: A form of vasculitis that can affect the gastrointestinal tract, among other systems, and cause inflammation and ulceration. It is rare and would be considered if there are other systemic symptoms or findings suggestive of vasculitis.