Differential Diagnosis for 81-year-old with Per Rectal Bleeding

Single Most Likely Diagnosis

• Graft infection with erosion into adjacent structures (e.g., bowel, aorta): Given the patient's history of EVAR with infection around the graft, this is a highly plausible cause for the rectal bleeding. The infection could have led to erosion into nearby structures, causing the active bleed. The elevated lactate levels and requirement for blood transfusion support the severity of the condition.

Other Likely Diagnoses

• Diverticulosis: A common cause of lower gastrointestinal bleeding in the elderly, especially with a history of iron deficiency anemia suggesting chronic blood loss.
• Angiodysplasia: Another possible cause of rectal bleeding in the elderly, which could be exacerbated by anticoagulation therapy (edoxaban for AF).
• Colorectal cancer: Although less likely given the acute presentation, it remains a possibility, especially in an elderly patient with iron deficiency anemia.

Do Not Miss Diagnoses

• Aorto-enteric fistula: A potentially life-threatening condition that could occur as a complication of the EVAR, especially with a history of graft infection. It is crucial to consider this diagnosis due to its high mortality if missed.
• Lower GI bleeding due to anticoagulation: The patient is on edoxaban for AF, which increases the risk of bleeding. Although the rectal bleeding could be due to other causes, the effect of anticoagulation must be considered, especially in managing the patient.

Rare Diagnoses

• Vasculitis: A less common cause of rectal bleeding, which could be considered if other diagnoses are ruled out and there are systemic symptoms suggestive of vasculitis.
• Intussusception: Although rare in adults, it could cause rectal bleeding and should be considered if there are other symptoms such as abdominal pain or a palpable mass.

Management Steps

1. Stabilization: Continue resuscitation efforts, including blood transfusions as needed, and monitor lactate levels to assess the effectiveness of resuscitation.
2. Imaging: Urgent CT angiography or MRI to evaluate the graft and surrounding structures for signs of infection, erosion, or fistula formation.
3. Endoscopy: Consider lower GI endoscopy to evaluate for other sources of bleeding such as diverticulosis, angiodysplasia, or colorectal cancer, once the patient is stabilized.
4. Anticoagulation Management: Consider reversing anticoagulation with appropriate agents (e.g., factor Xa inhibitors reversal with andexanet alfa) if the bleeding is thought to be exacerbated by edoxaban.
5. Surgical Consultation: Early involvement of vascular and general surgery teams for potential surgical intervention, especially if an aorto-enteric fistula or graft erosion is suspected.
6. Infection Management: Broad-spectrum antibiotics should be started empirically, with adjustment based on culture results, to manage or prevent further graft infection.