USMLE Step 3 - Question 4

A 62 year old male with a history of mitral valve prolapse, rhematoid arhtritis, and colon cancer presents to the emergency room with increased dyspnea on exertion, lower extremity swelling, and fevers slowly worsening over the past month. His temperature is 38.0 C, blood pressure 95/65, heart rate 80, respirations 20, and oxygen saturation 92% on room air. Physical examination reveals normal breath sounds, a II/VI holosystolic murmur at the apex, and 1+ bilateral lower extremity pitting edema. Laboratory studies show a WBC count of 20 thousand and an ESR of 100. A transesophageal  echocardiogram reveals an 8 mm mobile vegitation on the anterior leaflet of the mitral valve. Blood cultures grow Streptococcus bovis and he is treated appropriately with IV antibiotics for endocarditis. Which of the following further diagnostic work-up should be performed?

A. Coronary angiography

B. MRI of the brain

C. Pulmonary function testing

D. Colonoscopy

This case is a classic presentation of subacute endocarditis. Some pathogens are more aggressive than others and can actually present with septic shock such as Staph aureus and Pseudomonas auriginosa. Candidal endocarditis is rare in immunocompetent persons and the vegetation seen are quite large (usually > 1 cm). Streptococcus viridins group is the most common cause of endocarditis and presents in a subacute fashion (similar to Enterococcus endocarditis). Specifically, Streptococcus bovis (a type of Strep viridins) is strongly correlated with active colon cancer, thus if blood cultures were indeed positive for this organism, a colonoscopy should be performed at some point. Remember that the anterior leaflet of the mitral valve is the most common site for endocarditis. The holosystolic murmur at the apex likely represents mitral regurgitation due to valve destruction by the organism. Treatment includes at least 4-6 weeks of IV antibiotics which include penicillins or a third generation cephalosporin for Strep viridins, the combination ampicillin plus gentamicin for Enterococcus, nafcillin or oxacillin for penicillin sensitive Staph aureus, and vancomycin plus gentamicin for methacillin resistant Staph aureus (MRSA).