Differential Diagnosis for Microcytic Anemia in an Elderly Patient

Single Most Likely Diagnosis

• Iron Deficiency Anemia: This is the most common cause of microcytic anemia, especially in the elderly. It can result from chronic blood loss, inadequate dietary intake, or increased requirement for iron. In the elderly, chronic blood loss is a common cause, often due to gastrointestinal lesions such as ulcers or malignancies.

Other Likely Diagnoses

• Chronic Disease (Anemia of Chronic Disease): Conditions like chronic infections, autoimmune diseases, or malignancies can lead to microcytic anemia due to the body's inflammatory response affecting iron utilization and erythropoiesis.
• Thalassemia: While more common in younger populations, some forms of thalassemia can present later in life, especially if they are mild or if the patient has a thalassemia trait that becomes more symptomatic with age.
• Sideroblastic Anemia: This can be caused by various factors including genetics, drugs, or myelodysplastic syndromes, leading to impaired heme synthesis and resulting in microcytic anemia.

Do Not Miss Diagnoses

• Gastrointestinal Malignancy: As a cause of chronic blood loss leading to iron deficiency anemia, it's crucial to investigate and rule out gastrointestinal malignancies, especially in the elderly, due to their high mortality rate if left untreated.
• Peptic Ulcer Disease: As mentioned in the question, peptic ulcer disease can cause chronic blood loss leading to iron deficiency anemia. It's essential to consider this diagnosis due to its potential for severe complications if not treated.
• Colon Cancer: Similar to gastrointestinal malignancy, colon cancer can cause chronic blood loss and is a critical diagnosis not to miss due to its implications for patient outcomes.

Rare Diagnoses

• Lead Poisoning: Can cause microcytic anemia by inhibiting several steps in the heme biosynthetic pathway. While rare, it's an important consideration in patients with exposure history.
• Congenital Disorders: Such as congenital sideroblastic anemia, which can present later in life if mild, affecting heme synthesis and leading to microcytic anemia.
• Rare Genetic Disorders: Like X-linked sideroblastic anemia, which affects males and can present with microcytic anemia due to defects in the ATP-binding cassette B7 (ABCB7) gene affecting mitochondrial function and heme synthesis.