Infective endocarditis: Clinical

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Infective endocarditis: Clinical

USMLE® Step 2 questions

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A 67-year-old man presents to the primary care physician with a several week history of worsening fatigue, blurry vision, and rectal bleeding. Medical history is notable for ulcerative colitis, hypertension, and hyperlipidemia. The patient’s last colonoscopy was at age 50. Temperature is 37.6°C (99.7°F), pulse is 96/min, respirations are 18/min, and blood pressure is 122/63 mmHg. BMI is 34 kg/m2. Physical examination demonstrates an obese habitus. The patient’s skin appears pale with noted conjunctival pallor. Cardiopulmonary examination demonstrates a 3/6 holosystolic murmur best at the cardiac apex which was not present at the previous office visit 3 months ago. Retinal examination demonstrates round white spots on the retina surrounded by hemorrhage. Rectal examination is positive for scant blood in the rectal vault. Laboratory values are demonstrated below:  
Laboratory value  Result 
Complete Blood Count, Serum 
Hemoglobin  11.5 g/dL 
 Hematocrit  39.5% 
 Leukocyte count  14,100 /mm3 
 Platelet count  155,000/mm3 
Electrolytes, Serum 
                  Sodium                134 mEq/L 
               Potassium                 3.6 mEq/L 
                 Chloride                 97 mEq/L  
              Bicarbonate                 22 mEq/L 
                 Calcium                8.4 mg/dL 
Blood is drawn and sent for culture. Two days later, 3 of 4 blood cultures obtained grow Streptococcus gallolyticus (Streptococcus bovis biotype I). Which of the following studies is most likely to reveal the etiology of this patient’s infection?  


Infective endocarditis is an infection of the endocardium, the inner layer of the heart.

Most cases are due to a bacterial or fungal infection of the endocardial lining the heart valves.

But in order to reach the heart valves, a microbe has to first get into the bloodstream.

There are a few ways that might happen - microbes can hop into a blood vessel near an open wound or an abscess, or during a dental or surgical procedure, or they can go directly in when a person gets injected with an infected needle which sometimes happens while using illicit drugs.

Microbes generally like to latch onto heart valves that are already damaged, because it makes it easier for them to adhere and form vegetations.

Risk factors for infective endocarditis include cardiac factors, like prior infective endocarditis, a prosthetic valve or implantable cardiac device like a pacemaker, or valvular or congenital heart disease; and noncardiac factors like intravenous drug use, having an intravenous catheter, immunosuppression, or a recent dental or surgical procedure.

Clinically, infective endocarditis is categorized as either native valve endocarditis when it affects a previously normal heart valve, or prosthetic valve endocarditis when it affects an artificial heart valve.

Native valve endocarditis is mainly caused by Staphylococcus aureus, viridans Streptococci, and is often seen in intravenous drug users, since these bacteria are normally present in the skin.

Prosthetic valve endocarditis is mostly caused by Staphylococcus aureus as well - specifically methicillin resistant Staphylococcus Aureus or MRSA, since it’s frequently nosocomial.


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