A 23-year-old man comes to the office due to 3 weeks of malaise and fatigue. He says, "I've been sick with the flu for the last 3 weeks. I don't know why I'm not getting better." The patient also has profound fatigue causing difficulty with day-to-day activities. His temperature is 38.4 C (101.2 F). Cardiac auscultation reveals an apical holosystolic murmur radiating to the axilla, which was not heard during previous office visits. Laboratory evaluation shows serum creatinine of 2.3 mg/dL. Mild proteinuria and microscopic hematuria with red cell casts are present on urinalysis. Which of the following is the most likely pathogenesis of this patient's renal findings?

Question

A 23-year-old man comes to the office due to 3 weeks of malaise and fatigue.  He says, "I've been sick with the flu for the last 3 weeks.  I don't know why I'm not getting better."  The patient also has profound fatigue causing difficulty with day-to-day activities.  His temperature is 38.4 C (101.2 F).  Cardiac auscultation reveals an apical holosystolic murmur radiating to the axilla, which was not heard during previous office visits.  Laboratory evaluation shows serum creatinine of 2.3 mg/dL.  Mild proteinuria and microscopic hematuria with red cell casts are present on urinalysis.  Which of the following is the most likely pathogenesis of this patient's renal findings?

Quizplus · Accepted Answer

This young patient's constitutional (flulike) symptoms, fever, and a new systolic murmur suggest infective endocarditis (IE). Elevated serum creatinine with hematuria and proteinuria further suggest renal insufficiency due to a nephritic syndrome. In some patients, IE may be complicated by deposition of circulating immune complexes in the glomerular capillary wall, resulting in glomerulonephritis. This can be seen as capillary wall thickening with subendothelial and subepithelial deposit formation. Hypercellularity similar to that seen in poststreptococcal glomerulonephritis or membranoproliferative glomerulonephritis is revealed on light microscopy. (Choice A) Anti-glomerular basement membrane (anti-GBM) autoantibodies can also cause an acute nephritic syndrome. However, these antibodies do not affect cardiac tissues and would not cause a new cardiac murmur. Anti-GBM antibodies may target the pulmonary alveolar basement membrane, causing hemoptysis (Goodpasture syndrome). (Choice C) IE is rarely caused by gram-negative organisms, the producers of endotoxin. Furthermore, endotoxin production can cause acute tubular necrosis as part of sepsis but is unlikely to cause glomerulonephritis. (Choices D and E) Emboli from infected endocardial vegetations may metastasize via the hematogenous route to cause infarcts in the brain, kidneys, myocardium, and other tissues (eg, Janeway lesions on palms and soles). Emboli are usually small and do not cause acute renal failure. Renal failure may be seen if the infectious embolic focus develops into an abscess or the embolus is large enough to cause a sizeable infarct. However, both renal infarct and abscess present with flank pain. Educational objective: The most likely cause of fever and fatigue with new-onset cardiac murmur is infective endocarditis (IE). Diffuse, proliferative glomerulonephritis secondary to circulating immune complex deposition may complicate IE and can result in acute renal insufficiency.

A 23-Year-Old Man Comes to the Office Due to 3