Differential Diagnosis
The patient's symptoms of fever, weight loss, anorexia, nausea, vomiting, rectal bleeding, pallor, multiple aphthous ulcers in the oral cavity, and positive guaiac testing with abdominal tenderness suggest a gastrointestinal or inflammatory condition. Here is a categorized differential diagnosis:
Single most likely diagnosis
- Inflammatory Bowel Disease (IBD): The combination of rectal bleeding, abdominal tenderness, weight loss, and aphthous ulcers is highly suggestive of IBD, which includes conditions like Crohn's disease and ulcerative colitis. The presence of systemic symptoms such as fever and weight loss further supports this diagnosis.
Other Likely diagnoses
- Gastrointestinal Infection: Bacterial, viral, or parasitic infections could cause similar symptoms, including fever, abdominal pain, and rectal bleeding. However, the presence of aphthous ulcers and significant weight loss might lean more towards a chronic condition like IBD.
- Diverticulitis: This condition can cause abdominal pain, fever, and changes in bowel habits, including rectal bleeding. However, the presence of aphthous ulcers and significant systemic symptoms like weight loss is less typical for diverticulitis.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Intestinal Ischemia: Although less likely given the patient's age and symptom profile, intestinal ischemia can present with abdominal pain, vomiting, and rectal bleeding. It is a medical emergency that requires prompt diagnosis and treatment.
- Gastrointestinal Malignancy: While less common in younger patients, gastrointestinal cancers (e.g., colorectal cancer) can present with weight loss, anorexia, abdominal pain, and rectal bleeding. Early detection is crucial for treatment outcomes.
- Infectious Colitis (e.g., Clostridioides difficile): Especially in patients with recent antibiotic use or hospitalization, infectious colitis can cause severe diarrhea, abdominal pain, and potentially life-threatening complications if not treated promptly.
Rare diagnoses
- Behçet's Disease: A rare condition characterized by recurrent aphthous ulcers, genital ulcers, and ocular inflammation. Gastrointestinal involvement can mimic IBD, with symptoms including abdominal pain and rectal bleeding.
- Ehlers-Danlos Syndrome with Gastrointestinal Involvement: A genetic disorder that can lead to gastrointestinal symptoms due to bowel wall fragility and potential for perforation, although this would be an uncommon presentation.
- Chron's disease with extra intestinal manifestations: While not rare in itself, the combination of Crohn's disease with certain extra-intestinal manifestations (like aphthous ulcers) might be less common and could be considered under rare diagnoses depending on the context.