Differential Diagnosis for a 24-year-old Female with Diarrhea, Weight Loss, Dark/Black Stools, and Easy Bruising

• Single Most Likely Diagnosis
  • Inflammatory bowel disease (IBD) such as Crohn's disease or ulcerative colitis: This is likely due to the combination of chronic diarrhea, significant weight loss, and the presence of dark/black stools which could indicate gastrointestinal bleeding, all of which are common manifestations of IBD.
• Other Likely Diagnoses
  • Gastrointestinal infection: Certain infections can cause prolonged diarrhea, weight loss, and potentially bleeding, although the easy bruising might be less directly related.
  • Celiac disease: An autoimmune reaction to gluten can lead to malabsorption, diarrhea, weight loss, and potentially anemia (which could explain the easy bruising if it's severe enough to cause a significant drop in platelets or affect clotting factors).
  • Peptic ulcer disease: While less likely to cause significant weight loss and diarrhea, a bleeding peptic ulcer could explain the dark stools and, if severe, could lead to anemia and easy bruising.
• Do Not Miss Diagnoses
  • Colon cancer: Although rare in young adults, it's crucial not to miss this diagnosis, especially with symptoms like weight loss, changes in bowel habits, and gastrointestinal bleeding.
  • Lymphoma: Certain types of lymphoma can present with gastrointestinal symptoms, weight loss, and easy bruising due to bone marrow involvement.
  • Bleeding disorder (e.g., von Willebrand disease): If the easy bruising is a prominent symptom, a bleeding disorder should be considered, especially if there's a personal or family history of similar symptoms.
• Rare Diagnoses
  • Whipple's disease: A rare, systemic bacterial infection that can cause malabsorption, weight loss, diarrhea, and potentially bleeding.
  • Intestinal lymphangiectasia: A condition characterized by dilated lymphatic vessels in the intestines, leading to malabsorption, diarrhea, and potentially weight loss and easy bruising if there's significant protein loss.
  • Eosinophilic gastroenteritis: A rare condition involving eosinophilic infiltration of the gastrointestinal tract, which can cause a variety of symptoms including diarrhea, weight loss, and potentially gastrointestinal bleeding.

Each of these diagnoses should be considered in the context of the patient's full medical history, physical examination, and appropriate diagnostic testing to determine the underlying cause of her symptoms.