Differential Diagnosis for the 18-year-old Male Patient

The patient presents with symptoms of low exercise tolerance, syncopal episode during exertion, occasional ankle swelling, orthopnea, tachycardia, and mild cardiomegaly on chest X-ray. Considering these findings, the differential diagnoses can be categorized as follows:

• Single Most Likely Diagnosis
  • Chronic Anemia or Iron Deficiency Anemia: The patient's symptoms of low exercise tolerance, tachycardia, and syncopal episode could be indicative of anemia, which is a common condition that can lead to these symptoms due to reduced oxygen delivery to tissues.
• Other Likely Diagnoses
  • Atrial Septal Defect (ASD): The presence of mild cardiomegaly and symptoms of orthopnea and ankle swelling could suggest a left-to-right shunt, which is consistent with ASD.
  • Ventricular Septal Defect (VSD): Similar to ASD, VSD could explain the cardiomegaly and symptoms of heart failure, although it typically presents earlier in life.
  • Hypertrophic Cardiomyopathy: This condition could explain the low exercise tolerance, syncopal episode, and tachycardia, especially if there is outflow tract obstruction.
• Do Not Miss Diagnoses
  • Tetralogy of Fallot: Although less likely given the patient's age and the fact that TOF typically presents in infancy or early childhood, it is crucial not to miss this diagnosis due to its significant implications on morbidity and mortality if left untreated or undiagnosed.
  • Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): This condition can lead to sudden cardiac death, especially during exertion, making it a critical diagnosis not to miss.
  • Coronary Artery Anomalies: Anomalies in coronary artery origin or course can lead to ischemia and sudden cardiac death during exercise, emphasizing the importance of considering this in the differential diagnosis.
• Rare Diagnoses
  • Ebstein's Anomaly: A congenital heart defect involving the tricuspid valve, which could explain some of the patient's symptoms, although it is relatively rare.
  • Pulmonary Arterial Hypertension: This condition could lead to symptoms of low exercise tolerance, orthopnea, and tachycardia, but it would be less common in this age group without other underlying conditions.
  • Cardiac Sarcoidosis: Although rare, cardiac involvement in sarcoidosis can lead to heart failure symptoms, arrhythmias, and sudden death, making it a consideration in the differential diagnosis.