Differential Diagnosis

The patient's symptoms of diarrhea, significant weight loss, and positive stool lactoferrin and calprotectin suggest an underlying inflammatory or infectious process. Here's a categorized differential diagnosis:

• Single most likely diagnosis

  • Inflammatory Bowel Disease (IBD), specifically Crohn's disease or ulcerative colitis: The presence of elevated stool lactoferrin and calprotectin, which are markers of intestinal inflammation, along with chronic diarrhea and significant weight loss, strongly suggests IBD. These conditions are characterized by chronic inflammation of the gastrointestinal tract, leading to symptoms such as diarrhea, abdominal pain, and weight loss.

• Other Likely diagnoses

  • Infectious colitis (e.g., Clostridioides difficile infection): While less likely than IBD given the chronic nature of symptoms and significant weight loss, infectious causes can also elevate stool lactoferrin and calprotectin. C. difficile infection is a common cause of diarrhea and can be particularly severe.
  • Microscopic colitis: This condition, which includes lymphocytic and collagenous colitis, can cause chronic diarrhea and weight loss. However, it typically has a more subtle onset and might not elevate inflammatory markers as significantly as IBD.
  • Small intestine bacterial overgrowth (SIBO): SIBO can cause diarrhea, weight loss, and malabsorption. While it might not directly elevate lactoferrin and calprotectin, it could contribute to an inflammatory state in the gut.

• Do Not Miss diagnoses

  • Colorectal cancer: Although less common, especially in younger patients, colorectal cancer can present with chronic diarrhea, weight loss, and elevated inflammatory markers. It is crucial to rule out this diagnosis, especially given the significant weight loss.
  • Whipple's disease: A rare, systemic bacterial infection that can cause malabsorption, diarrhea, weight loss, and arthralgias. It's essential to consider due to its potential for severe complications if left untreated.
  • Lymphoma: Gastrointestinal lymphoma can cause similar symptoms, including diarrhea and significant weight loss. It's a critical diagnosis not to miss due to its implications for treatment and prognosis.

• Rare diagnoses

  • Eosinophilic gastroenteritis: A rare condition characterized by eosinophilic infiltration of the gastrointestinal tract, leading to symptoms like diarrhea, abdominal pain, and weight loss.
  • Chronic intestinal ischemia: Reduced blood flow to the intestines can cause chronic diarrhea, weight loss, and abdominal pain, especially after eating. This condition is more common in older patients with atherosclerotic disease.
  • Autoimmune enteropathy: A rare condition characterized by autoimmune destruction of the intestinal lining, leading to severe diarrhea, malabsorption, and weight loss.