In a 29-year-old asymptomatic man with a pansystolic murmur radiating to the axilla, what is the most likely cause?

Most Likely Diagnosis: Mitral Valve Prolapse

In a 29-year-old asymptomatic man with a pansystolic murmur radiating to the axilla, mitral valve prolapse (MVP) is the most likely diagnosis. 1, 2

Clinical Reasoning

Why MVP is Most Likely

• MVP is the most common valvular disorder in the United States, occurring in 1-2.5% of the population, with peak clinical manifestation in the second and third decades of life 1, 3

• The pansystolic murmur radiating to the axilla is pathognomonic for mitral regurgitation, specifically indicating anterior leaflet pathology, and MVP can progress from a late systolic murmur to a pansystolic murmur when regurgitation becomes more severe 1, 2

• The asymptomatic presentation in a young adult during routine screening strongly favors MVP as the underlying etiology, since most patients with MVP remain asymptomatic throughout life with a benign prognosis 1

• Young individuals with MVP are typically of slender body habitus, reflecting higher rates of linear growth during adolescent growth spurts 3

Why Other Options Are Less Likely

Ischemic mitral regurgitation (Option B):

• Extremely unlikely in a 29-year-old asymptomatic patient with no history suggesting coronary artery disease 1
• Ischemic MR typically occurs in patients with prior myocardial infarction causing papillary muscle dysfunction 1

Functional mitral regurgitation (Option C):

• Functional MR produces a midsystolic murmur, NOT a pansystolic murmur 1, 2
• Occurs secondary to left ventricular dilation from cardiomyopathy or heart failure, which would produce symptoms 1

Rheumatic mitral regurgitation (Option D):

• Less likely because rheumatic heart disease has markedly decreased prevalence in industrialized countries 1
• Typically presents with mixed valvular disease and a symptomatic history 1
• While rheumatic fever can cause MVP in some cases, the asymptomatic presentation in a young adult during routine screening makes primary MVP more likely 4

Diagnostic Confirmation

Echocardiography should be performed to confirm MVP, assess mitral regurgitation severity, evaluate leaflet morphology (particularly looking for thickened leaflets ≥5 mm which indicate higher complication risk), and assess ventricular compensation 1, 2

Dynamic auscultation can support the diagnosis:

• The murmur typically becomes louder with Valsalva maneuver or standing (which decreases preload and increases prolapse) 1, 2
• The murmur softens with squatting (which increases preload and reduces prolapse) 5, 1, 2

Clinical Pitfalls to Avoid

• The click-murmur of MVP may be misdiagnosed as a benign flow murmur if the ejection click is not recognized 5, 2
• Do not assume all pansystolic murmurs in young patients are benign - echocardiography is essential to assess severity and guide follow-up 2
• Patients with thickened mitral valve leaflets (≥5 mm) have increased risk of complications including endocarditis, progressive MR requiring surgery, and arrhythmias 1

Prognosis

• MVP has a benign prognosis in most patients, with age-adjusted survival similar to the general population 1
• Complication rate is approximately 2% per year, with approximately 5% of affected men and 1.5% of affected women ultimately requiring valve surgery 1
• Most patients remain asymptomatic throughout life, though follow-up intensity should be guided by the presence and severity of mitral regurgitation 6