Differential Diagnosis for the 73-year-old Male Patient

Single Most Likely Diagnosis

• Anemia exacerbation due to chronic gastrointestinal blood loss: The patient has a history of chronic iron deficiency anemia, intestinal polyps, and recent positive fecal occult blood tests, suggesting ongoing gastrointestinal blood loss. This, combined with his increased dyspnea and decreased exercise tolerance, points towards anemia as a primary contributor to his current symptoms.

Other Likely Diagnoses

• Congestive Heart Failure (CHF) exacerbation: Given the patient's history of coronary artery disease, hypertension, and mitral valve replacement, CHF is a plausible diagnosis. His symptoms of increased dyspnea and decreased exercise tolerance could be indicative of worsening heart failure, especially considering the recent initiation of furosemide.
• Gout flare: The patient presents with localized swelling and pain in his right foot, consistent with a gout flare, which is supported by his history of gout.
• Volume depletion: The patient's recent euvolemic anemia and history of being in a low volume state, possibly exacerbated by furosemide, could contribute to his symptoms of dyspnea and fatigue.

Do Not Miss Diagnoses

• Pulmonary Embolism (PE): Although the patient does not exhibit classic red flag symptoms for PE, such as chest pain or syncope, his history of recent hospitalization, immobilization, and possible chronic thromboembolic disease due to his mechanical valve necessitates consideration of this potentially life-threatening condition.
• Infective Endocarditis: Despite the lack of overt signs of infection, the patient's history of a mechanical mitral valve and recent hospitalizations increases his risk for infective endocarditis, which can present subtly and requires prompt diagnosis and treatment.
• Acute Coronary Syndrome: The patient's history of coronary artery disease and recent increase in dyspnea warrant consideration of an acute coronary syndrome, even in the absence of chest pain, as atypical presentations are more common in older adults.

Rare Diagnoses

• Thrombosis of the mechanical mitral valve: Although rare, thrombosis of a mechanical valve is a life-threatening condition that could explain the patient's symptoms of increased dyspnea and decreased exercise tolerance.
• Paroxysmal Nocturnal Hemoglobinuria (PNH) or other rare causes of anemia: Given the patient's chronic anemia and gastrointestinal blood loss, rare causes of anemia such as PNH could be considered, especially if common causes are ruled out.