Differential Diagnosis for Mid-Systolic, Crescendo-Decrescendo Murmur

• Single most likely diagnosis
  • Aortic Stenosis (AS): The mid-systolic, crescendo-decrescendo murmur that is loudest at the left lower sternal border (LLSB) and increases with the Valsalva maneuver is highly suggestive of AS. The Valsalva maneuver increases the intensity of the murmur in AS due to the decreased venous return, which increases the velocity of blood flow across the stenotic valve.
• Other Likely diagnoses
  • Pulmonary Stenosis (PS): Although less common, PS can also present with a mid-systolic, crescendo-decrescendo murmur. However, the murmur of PS is typically loudest at the left upper sternal border (LUSB) and may radiate to the back. The increase with Valsalva can be seen but is more characteristic of AS.
  • Hypertrophic Obstructive Cardiomyopathy (HOCM): HOCM can present with a similar murmur, which is typically loudest at the LLSB and increases with maneuvers that decrease ventricular volume, such as the Valsalva maneuver. However, the murmur of HOCM is often more variable and can be affected by different maneuvers and positions.
• Do Not Miss diagnoses
  • Subvalvular Aortic Stenosis: This condition can present similarly to valvular AS but is due to a narrowing below the aortic valve. It's crucial to identify as it may require different management strategies.
  • Supravalvular Aortic Stenosis: A narrowing above the aortic valve, which can also present with a similar murmur. It's essential to distinguish from valvular AS due to its different implications for management and prognosis.
• Rare diagnoses
  • Discrete Subaortic Stenosis: A rare condition where there is a narrowing just below the aortic valve, which can cause a similar murmur.
  • Bicuspid Aortic Valve with Stenosis: While bicuspid aortic valve is a common congenital heart defect, significant stenosis presenting in this manner is less common and would typically be identified earlier in life. However, it can be a cause of aortic stenosis and should be considered, especially in younger patients.