A 27-year-old man who recently emigrated as a refugee from Somalia presents with fever, weight loss, fatigue, and exertional chest pain. He says his symptoms began 3 weeks ago and that his appetite has decreased and he has lost 3 kg (6.6 lb) in the last 3 weeks. He denies any history of cardiac disease. His past medical history is unremarkable. The patient admits that he has always lived in poor hygienic conditions in overcrowded quarters and in close contact with cats. His vital signs include: blood pressure 120/60 mm Hg, pulse 90/min, and temperature 38.0°C (100.4°F). Physical examination reveals generalized pallor. A cardiac examination reveals an early diastolic murmur loudest at the left third intercostal space. Abdominal examination reveals a tender and mildly enlarged spleen. Prominent axillary lymphadenopathy is noted. Laboratory investigations reveal a WBC count of 14,500/μL with 5% bands and 93% polymorphonuclear cells. An echocardiogram reveals a 5-mm vegetation on the aortic valve with moderate regurgitation. Three sets of blood cultures are taken over 24 hours followed by empiric antibiotic therapy with gentamicin and vancomycin. The blood cultures show no growth after 5 days. Following a week of empiric therapy, the patient continues to deteriorate. Which of the following would most likely confirm the diagnosis in this patient?

Epstein-Barr virus heterophile antibody

A 38-year-old female presents to the emergency room with fevers, fatigue, and anorexia for over a month. Past medical history includes mild mitral valve prolapse. She underwent an uncomplicated tooth extraction approximately 6 weeks ago. Her vital signs include a temperature of 100.8 F, pulse of 83, blood pressure of 110/77, and SpO2 of 97% on room air. On exam, you note a grade III/VI holosystolic murmur at the apex radiating to the axilla as well as several red, painful nodules on her fingers. Which of the following is the next best course of action?

Obtain blood cultures x3 sites over 1 hour and start empiric antibiotics

Blood cultures are not needed. Start empiric antibiotics

Start anticoagulation with heparin

Consult cardiothoracic surgery for mitral valve replacement

Obtain blood cultures x3 sites over 24 hours and start antibiotics after culture results are available

A 27-year-old man presents to the emergency department with weakness and a fever for the past week. The patient is homeless and has a past medical history of alcohol and IV drug abuse. His temperature is 102°F (38.9°C), blood pressure is 107/68 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for a tremulous patient with antecubital scars and a murmur over the left lower sternal border. Blood cultures are drawn and the patient is started on vancomycin and ceftriaxone and is admitted to the ICU. The patient's fever and symptoms do not improve despite antibiotic therapy for which the initial identified organism is susceptible. Cultures currently reveal MRSA as one of the infective organisms. Which of the following is the best next step in management?

Transesophageal echocardiography

Nafcillin and piperacillin-tazobactam

A 51-year-old man comes to the physician for 2 months of intermittent low-grade fever, malaise, and joint pain. He has a history of recurrent dental abscesses requiring drainage but has otherwise been healthy. His temperature is 38.3°C (100.9°F) and pulse is 112/min. Physical examination shows a new holosystolic murmur in the left midclavicular line that radiates to the axilla. There are linear reddish-brown lesions underneath the nail beds and tender violaceous nodules on the bilateral thenar eminences. Two sets of blood cultures grow Streptococcus mutans. A transthoracic echocardiogram shows moderate regurgitation of the mitral valve. Which of the following mechanisms is most likely directly involved in the pathogenesis of this patient's valvular condition?

Leaflet calcification and fibrosis

Sterile platelet thrombi deposition

A 61-year-old man with a history of stage IIIa lung adenocarcinoma that has been treated with wedge resection and chemotherapy presents to the primary care clinic. He is largely asymptomatic, but he demonstrates a persistent microcytic anemia despite iron supplementation. Colonoscopy performed 3 years earlier was unremarkable. His past medical history is significant for diabetes mellitus type II, hypertension, acute lymphoblastic leukemia as a child, and hypercholesterolemia. He currently smokes 1 pack of cigarettes per day, drinks a glass of pinot grigio per day, and currently denies any illicit drug use. His vital signs include: temperature, 36.7°C (98.0°F); blood pressure, 126/74 mm Hg; heart rate, 87/min; and respiratory rate, 17/min. On physical examination, his pulses are bounding, complexion is pale, but breath sounds remain clear. Oxygen saturation was initially 91% on room air, with a new oxygen requirement of 2 L by nasal cannula. Which of the following lab values would suggest anemia of chronic disease as the underlying etiology?

Decreased serum iron and transferrin, increased ferritin, normal serum transferrin receptor

Decreased serum iron and transferrin, decreased ferritin, normal serum transferrin receptor

Increased serum iron and transferrin, increased ferritin, normal serum transferrin receptor

Decreased serum iron, increased transferrin, decreased ferritin, increased serum transferrin receptor

Decreased serum iron, decreased transferrin, increased ferritin, increased serum transferrin receptor

Infective endocarditis for USMLE Step 1: High-Yield Pathology Lessons

Infective Endocarditis - Heart's Unwanted Guests

Microbial invasion of heart valves or endocardium, forming vegetations (platelet-fibrin-microbe mesh).
Acute: S. aureus (high virulence, native valves). Subacute: S. viridans (low virulence, damaged valves). Prosthetic valve: S. epidermidis. IVDU: S. aureus (tricuspid).
📌 FROM JANE: Fever, Roth spots, Osler nodes, Murmur, Janeway lesions, Anemia, Nail-bed hemorrhages, Emboli.

⭐ Streptococcus bovis (gallolyticus) endocarditis has a strong association with colorectal cancer; colonoscopy is mandatory.

Pathophysiology - Seeding the Valves

Starts with endothelial injury (e.g., turbulent flow, catheter).
This triggers platelet-fibrin deposition, forming a sterile thrombus (Nonbacterial Thrombotic Endocarditis, NBTE).
Transient bacteremia introduces microorganisms.
Bacteria adhere to the NBTE nidus via adhesin proteins.
Proliferation within a biofilm creates the mature, protected vegetation.

Infective Endocarditis Pathophysiology

⭐ Staphylococcus aureus is highly virulent; its fibronectin-binding proteins allow it to adhere directly to both damaged and intact endothelium, bypassing the need for prior NBTE.

Clinical Features - FROM JANE with Love

📌 FROM JANE

Fever: Most common finding.
Roth spots: Retinal hemorrhages with pale centers.
Osler nodes: Tender subcutaneous nodules on digits (Ouch!).
Murmur: New or worsening heart murmur (usually regurgitant).
Janeway lesions: Non-tender erythematous macules on palms/soles.
Anemia: Anemia of chronic disease.
Nail-bed hemorrhages: Splinter hemorrhages.
Emboli: Septic emboli to brain, spleen, kidney.

Clinical signs of infective endocarditis

⭐ In IV drug users, suspect tricuspid valve endocarditis, often caused by S. aureus. Murmur may be subtle or absent.

Diagnosis - The Duke's Decree

Requires: 2 Major, OR 1 Major + 3 Minor, OR 5 Minor criteria.

Major Criteria:
- Blood cultures positive for typical IE organisms from 2 separate samples.
- Evidence of endocardial involvement on echocardiogram (vegetation, abscess) or new valvular regurgitation.
Minor Criteria: 📌 FROM JANE
- Fever >38°C
- Risk factor (e.g., IVDU, prosthetic valve)
- Osler's nodes, Microbiologic evidence (not major)
- Janeway lesions, Arterial emboli, Nephritis (glomerulo-), Echo findings (not major)

Modified Duke Criteria for Infective Endocarditis

⭐ Culture-negative endocarditis is often caused by Coxiella burnetii, Bartonella spp., or the HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella).

Management & Prophylaxis - Bug Battle Plan

Specific Therapy:
- Staph aureus (MSSA): Nafcillin/Oxacillin
- Strep viridans: Penicillin G or Ceftriaxone
Prophylaxis: Amoxicillin for high-risk patients (prosthetic valves, prior IE) before dental or respiratory procedures.

⭐ Aminoglycosides (e.g., Gentamicin) create pores in the bacterial cell wall, enhancing the entry of cell-wall active agents like Penicillin or Vancomycin.

S. aureus is the most common cause, especially in IV drug users affecting the tricuspid valve.

Strep viridans causes subacute IE, typically after dental procedures on damaged native valves.

S. epidermidis is a primary cause of prosthetic valve endocarditis.

An association with S. bovis (gallolyticus) strongly suggests underlying colon cancer.

Classic signs: Fever, new murmur, Janeway lesions (painless), Osler nodes (painful), Roth spots.

Diagnosis is based on Duke criteria, requiring positive blood cultures and echocardiogram findings.

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