A 35-year-old African-American female presents to the emergency room complaining of chest pain. She also complains of recent onset arthritis and increased photosensitivity. Physical examination reveals bilateral facial rash. Which of the following is most likely to be observed in this patient?

Pain relieved by sitting up and leaning forward

An autopsy of a patient's heart who recently died in a motor vehicle accident shows multiple nodules near the line of closure on the ventricular side of the mitral valve leaflet. Microscopic examination shows that these nodules are composed of immune complexes, mononuclear cells, and thrombi interwoven with fibrin strands. These nodules are most likely to be found in which of the following patients?

A 41-year-old female with a facial rash and nonerosive arthritis

A 6-year-old female with subcutaneous nodules and erythema marginatum

A 62-year-old male with Cardiobacterium hominis bacteremia

A 54-year-old male who recently underwent dental surgery

A 71-year-old male with acute-onset high fever and nail bed hemorrhages

A 16-year-old female is seen at her outpatient primary medical doctor's office complaining of a sore throat. Further history reveals that she has no cough and physical exam is notable for tonsillar exudates. Vitals in the office reveal HR 88, RR 16, and T 102.1. Using the Centor criteria for determining likelihood of Group A beta-hemolytic strep pharyngitis, the patient has a score of 3. A review of the primary literature yields the findings in Image A. What is the specificity of the Centor criteria using a score of 3 as a cutoff value?

Not enough information has been provided

A 27-year-old woman comes to the physician because of a 3-day history of a sore throat and fever. Her temperature is 38.5°C (101.3°F). Examination shows edematous oropharyngeal mucosa and enlarged tonsils with purulent exudate. There is tender cervical lymphadenopathy. If left untreated, which of the following conditions is most likely to occur in this patient?

Post-streptococcal glomerulonephritis

A 43-year-old woman presents to the emergency department complaining of palpitations, dry cough, and shortness of breath for 1 week. She immigrated to the United States from Korea at the age of 20. She says that her heart is racing and she has never felt these symptoms before. Her cough is dry and is associated with shortness of breath that occurs with minimal exertion. Her past medical history is otherwise unremarkable. She has no allergies and is not currently taking any medications. She is a nonsmoker and an occasional drinker. She denies illicit drug use. Her blood pressure is 100/65 mm Hg, pulse is 76/min, respiratory rate is 23/min, and temperature is 36.8°C (98.2°F). Her physical examination is significant for bibasilar lung crackles and a non-radiating, low-pitched, mid-diastolic rumbling murmur best heard at the apical region. In addition, she has jugular vein distention and bilateral pitting edema in her lower extremities. Which of the following best describes the infectious agent that led to this patient’s condition?

A bacterium that induces complete lysis of the red cells of a blood agar plate with an oxygen-sensitive cytotoxin

A bacterium that induces partial lysis of red cells with hydrogen peroxide

A bacterium that requires an anaerobic environment to grow properly

A bacterium that does not lyse red cells

A bacterium that induces heme degradation of the red cells of a blood agar plate

A 51-year-old woman with hyperlipidemia comes to the physician because of weakness for one month. At the end of the day, she feels too fatigued to cook dinner or carry a laundry basket up the stairs. She also complains of double vision after she reads for long periods of time. All of her symptoms improve with rest. Her only medication is pravastatin. Physical examination shows drooping of the upper eyelids. Strength is initially 5/5 in the upper and lower extremities but decreases to 4/5 after a few minutes of sustained resistance. Sensation to light touch is intact and deep tendon reflexes are normal. Which of the following best describes the pathogenesis of this patient's condition?

Type II hypersensitivity reaction

Rheumatic heart disease for USMLE Step 2 CK: High-Yield Pathology Lessons

Etiopathogenesis - Strep's Sneaky Attack

Trigger: Untreated Group A β-hemolytic Streptococcus pyogenes pharyngitis.
Mechanism: Type II Hypersensitivity via molecular mimicry.
- Strep M-protein & N-acetyl-beta-D-glucosamine resemble human cardiac antigens (myosin, laminin).
- Antibodies produced against Strep cross-react with host cardiac tissues.
Timeline: Acute rheumatic fever develops 2-4 weeks after the initial strep throat infection.

⭐ Histopathologic Hallmark: Aschoff bodies (granulomas with fibrinoid necrosis) containing Anitschkow cells ("caterpillar cells" with wavy nuclei) are pathognomonic for acute rheumatic carditis.

Acute Rheumatic Fever - Jones's Rules of the Game

Diagnosis requires evidence of a preceding Group A Strep infection + 2 major criteria OR 1 major & 2 minor criteria.

📌 Mnemonic: JONES

Major Criteria	Minor Criteria
Joints (migratory polyarthritis)	Arthralgia
O (Carditis)	Fever (≥38.5°C / 101.3°F)
Nodules (subcutaneous)	Elevated ESR or CRP
Erythema marginatum	Prolonged PR interval
Sydenham chorea

⭐ Carditis is the most severe sign, potentially affecting all heart layers (pancarditis). It is the only major criterion that can lead to permanent damage, most commonly causing mitral regurgitation in the acute phase.

Cardiac Pathology - The Heart's Scars

Gross Findings:
- Pericardium: Fibrinous pericarditis ("bread and butter" appearance).
- Valves (Chronic): Leaflet thickening, commissural fusion, and chordae tendineae shortening leading to "fish-mouth" or "buttonhole" stenosis. Most commonly affects mitral valve.
- Endocardium: MacCallum patches (irregular thickening) in the left atrium.
Microscopic Hallmark:
- Aschoff Body: The pathognomonic finding. A focus of fibrinoid necrosis surrounded by inflammatory cells.
- Anitschkow Cells: Plump macrophages with caterpillar-like chromatin found within Aschoff bodies.

Aschoff body and Anitschkow cells in rheumatic heart disease

⭐ Chronic rheumatic heart disease is overwhelmingly the most frequent cause of mitral stenosis.

Chronic RHD & Management - The Long Game

Pathology: Progressive, irreversible valve fibrosis developing years after ARF. Mitral valve is most affected (>85%), leading to classic "fish-mouth" or "buttonhole" stenosis. Aschoff bodies are replaced by fibrous scar tissue.
Clinical Course: A long latent period, often 10-20 years, between the initial ARF and the onset of clinical symptoms.
Common Sequelae:
- Mitral stenosis (most common) → LA enlargement → Atrial fibrillation → Thromboembolism risk.
- Mitral regurgitation.
- Aortic valve disease (stenosis/regurgitation) is less frequent.
Management:
- Focuses on complications: Diuretics, rate control (β-blockers), and anticoagulation for AFib.
- Surgical: Valve repair or replacement for severe, symptomatic disease.

Rheumatic Heart Disease: "Fish-Mouth" Mitral Valve

⭐ The clinical features of chronic RHD, particularly mitral stenosis, typically manifest 10-20 years after the initial episode of acute rheumatic fever, highlighting a significant asymptomatic latent period.

Results from molecular mimicry following Group A Strep pharyngitis (Type II hypersensitivity).

Aschoff bodies (pathognomonic granulomas) and Anitschkow cells are key histologic findings.

Acute phase presents as a pancarditis affecting all heart layers.

Mitral valve is most commonly affected, leading to chronic stenosis; aortic valve is second.

Diagnosis relies on Jones criteria and evidence of recent strep infection.

Chronic RHD causes "fish-mouth" deformity and ↑ risk of atrial fibrillation.

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