USMLE USMLE Certifications USMLE Questions & Answers

• Question 621:

  A 37-year-old woman presents to the emergency department with a fever. Chest x-ray film shows multiple patchy infiltrates in both lungs. Echocardiography and blood cultures suggest a diagnosis of acute bacterial endocarditis limited to the tricuspid valve. Which of the following is the most probable etiology?

  A. Congenital heart disease

  B. Illicit drug use

  C. Rheumatic fever

  D. Rheumatoid arthritis

  E. Systemic lupus erythematosus

  Correct Answer: B

  Explanation:

  The most probable etiology of bacterial endocarditis involving the tricuspid valve is illicit IV drug use, which can introduce skin organisms into the venous system that then attack the tricuspid valve. Staphylococcus aureus accounts for between 60% and 90% of cases of endocarditis in IV drug users. The endocarditis associated with congenital heart disease typically involves either damaged valves or atrial or ventricular septal defects. The tricuspid valve is not particularly vulnerable. Rheumatic fever most commonly damages the mitral and aortic valves, and tricuspid damage is usually less severe and seen only when the mitral and aortic valves are heavily involved. Consequently, secondary bacterial endocarditis involving only the tricuspid valve in a patient with history of rheumatic fever would be unusual. Rheumatoid arthritis is not associated with bacterial endocarditis. Systemic lupus erythematosus can produce small, aseptic vegetations on valves, but is not associated with bacterial endocarditis.

• Question 622:

  An adult patient presents with persistent headaches. A CT scan of the head demonstrates a 2-cm spherical mass at the junction of the white and gray matter of the lateral aspect of the cerebral hemisphere. Which of the following would most likely produce this lesion?

  A. Astrocytoma

  B. Ependymoma

  C. Glioblastoma multiforme

  D. Meningioma

  E. Metastatic carcinoma

  Correct Answer: E

  Explanation:

  Seventy percent of adult brain tumors occur above the tentorium (70% of childhood tumors occur below the tentorium). Statistically, metastases > astrocytomas (including glioblastoma) > meningioma > pituitary tumor. Location at the junction of cortical gray and white matter is also typical for metastatic disease, as is the round shape. Astrocytomas typically arise in the white matter and have an irregular shape. Ependymomas are uncommon and arise from the ependymal lining of the ventricles. Glioblastoma multiforme is an aggressive form of astrocytoma that can cause a “butterfly lesion,” crossing between the cerebral hemispheres. Meningiomas can cause spherical lesions and are usually located on the surface of the brain.