In an asymptomatic 29‑year‑old man examined in a pre‑employment clinic who has a pansystolic murmur radiating to the left axilla, what is the most likely cause?

Most Likely Diagnosis: Mitral Valve Prolapse

In an asymptomatic 29-year-old man with a pansystolic murmur radiating to the axilla discovered on routine examination, mitral valve prolapse (MVP) is by far the most likely diagnosis. 1

Epidemiologic Support

• MVP is the most common valvular disorder in the United States, affecting approximately 1–2.5% of the general population, with peak clinical manifestation typically occurring in the third and fourth decades of life. 1, 2

• The asymptomatic presentation in a young adult undergoing routine pre-employment screening strongly favors MVP as the underlying etiology. 3

Auscultatory Features Consistent with MVP

• While the classic auscultatory hallmark of MVP is a midsystolic click followed by a late-systolic murmur, the murmur can range from a brief, faint sound to a holosystolic (pansystolic) murmur depending on the severity of regurgitation. 1

• A pansystolic murmur radiating to the axilla can become holosystolic when regurgitation is more severe in MVP, even while the patient remains asymptomatic. 3

• The pansystolic murmur radiating to the axilla is characteristic of mitral regurgitation, and when MVP progresses, it can present with either a late systolic murmur or a pansystolic murmur depending on severity. 3

• In one clinical series, 16% of patients with echocardiographically confirmed MVP had pansystolic murmurs, with the incidence of murmurs rising with increasing age. 4

Why Other Options Are Unlikely

Ischemic mitral regurgitation (Option B):

• Ischemic mitral regurgitation is improbable in a young, asymptomatic adult without a history of coronary artery disease or myocardial infarction. 1
• This condition typically occurs in patients with coronary artery disease and prior myocardial infarction causing papillary muscle dysfunction. 3

Functional mitral regurgitation (Option C):

• Functional mitral regurgitation typically presents with a midsystolic murmur, not a pansystolic murmur. 1, 3
• It occurs secondary to left-ventricular dilation from cardiomyopathy or heart failure, which would usually be symptomatic. 1

Rheumatic mitral regurgitation (Option D):

• Rheumatic mitral regurgitation is rare in industrialized nations and has markedly decreased prevalence. 1, 3
• It is usually preceded by a symptomatic episode of acute rheumatic fever and often appears as mixed valvular disease. 1
• While rheumatic fever can cause MVP in some cases, the lack of documented rheumatic fever history and the isolated finding make primary MVP far more likely. 5

Diagnostic Confirmation

• Transthoracic echocardiography is recommended to confirm MVP, evaluate the severity of mitral regurgitation, assess leaflet morphology, and examine ventricular compensation. 1

• Dynamic auscultation should be performed: performing the Valsalva maneuver or standing reduces left-ventricular end-diastolic volume, causing the click-murmur complex to occur earlier in systole, while squatting increases left-ventricular volume, shifting it later in systole. 1, 3

Prognosis and Risk Stratification

• In the majority of individuals, MVP follows a benign course with age-adjusted survival comparable to that of the general population and an overall complication rate of about 2% per year. 1

• Leaflet thickness of ≥5 mm is considered abnormal and identifies patients at higher risk for complications such as infective endocarditis, progressive regurgitation requiring surgery, and arrhythmias. 1

• Approximately 5% of affected men and 1.5% of affected women eventually require mitral valve surgery. 1