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Difficulty: HardFormulating a Differential Diagnosis

A 42-year-old woman presents to the clinic complaining of progressively worsening fatigue, low-grade fevers, and intermittent pain in her wrists and knees for the past 8 weeks. She also reports a 4-kg (9-lb) unintentional weight loss during this period. Over the last week, she has experienced three episodes of lightheadedness and transient shortness of breath. These episodes notably occur when she sits upright in a chair and resolve rapidly when she lies flat. Her temperature is 37.8°C (100.0°F), blood pressure is 110/70 mm Hg, and pulse is 88/min. Cardiac auscultation reveals a low-pitched, mid-diastolic rumble at the apex. A distinct, low-frequency sound is heard shortly after the second heart sound. The intensity of the diastolic murmur noticeably increases when she sits up. Lungs are clear to auscultation. Skin examination reveals scattered petechiae on her lower extremities. Laboratory studies show:

Hemoglobin: 10.4 g/dL
Leukocytes: 11,200/mm³
Erythrocyte sedimentation rate: 85 mm/h
Rheumatoid factor: Positive
Blood cultures: Pending

Which of the following is the most likely diagnosis?

  1. Left atrial myxomaAnswer
  2. B
    Infective endocarditis
  3. C
    Rheumatoid arthritis
  4. D
    Nonbacterial thrombotic endocarditis
  5. E
    Acute rheumatic fever

Answer

The most likely diagnosis is a left atrial myxoma.
The correct answer perfectly unifies the patient's seemingly disparate symptoms. Left atrial myxomas are the most common primary cardiac tumors. They frequently secrete interleukin-6 (IL-6), a pro-inflammatory cytokine that leads to constitutional symptoms (fever, weight loss), arthralgias, elevated ESR, and even a reactive positive rheumatoid factor—often leading to misdiagnosis of an autoimmune disease or infective endocarditis. The mobile nature of the tumor on a stalk allows it to prolapse into the mitral valve orifice during diastole. This causes a mid-diastolic rumble mimicking mitral stenosis, and the impact of the tumor against the valve produces a characteristic early diastolic 'tumor plop'. Because gravity affects the tumor's position, the obstruction—and consequently the murmur, dyspnea, and lightheadedness—is highly dependent on body position, typically worsening when the patient is upright. Finally, friable tumor fragments can embolize, causing petechiae.

Step-by-Step Solution

1
Analyze the systemic and laboratory findings.
The patient has subacute fever, weight loss, fatigue, an elevated ESR, and a positive rheumatoid factor, indicating a profound systemic inflammatory state.
Identifying the systemic component helps narrow the differential to infectious, autoimmune, or specific neoplastic etiologies.
2
Evaluate the cardiac auscultatory findings.
A mid-diastolic rumble with an early diastolic sound (tumor plop) is present.
These findings localize the pathology to the mitral valve region, mimicking mitral stenosis.
3
Synthesize the mechanical/positional clues with the systemic presentation.
The patient experiences dyspnea and lightheadedness when upright that resolves when supine, and the murmur intensity changes with position. This highly specific positional dependence points to a mobile mass obstructing the mitral orifice rather than a fixed valvular lesion.
Left atrial myxomas frequently secrete interleukin-6 (IL-6), which explains all the systemic autoimmune/infectious-like symptoms (including the reactive positive RF), while the physical mass effect explains the positional obstruction and embolic petechiae.

Key Concept

Clinical presentation and differential diagnosis of cardiac myxomas
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Topics

Formulating a Differential Diagnosis

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