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PATIENT 
Mrs. L is a 58-year-old woman who arrives at the emergency department with a chief complaint of shortness of breath. She reports that this has developed gradually over the last 3–6 months. Six months ago, she was able to walk as far as she wanted without any shortness of breath. Now she is experiencing dyspnea even walking around her house. She denies any episodes of acute shortness of breath, fever, chest pain, or hemoptysis. She denies wheezing. She has no history of MI, hypertension, or known heart disease. She smoked 1 pack of cigarettes per day for 10 years and quit when she was 28 years old. She has no history of prior venous thromboembolism (VTE), cancer, or immobilization. She drinks 1 glass of wine per week. She works as an accountant and spends her free time with her grandchildren. She has no unusual hobbies.
At this point, what is the leading hypothesis, what are the active alternatives, and is there a must not miss diagnosis? Given this differential diagnosis, what tests should be ordered?
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RANKING THE DIFFERENTIAL DIAGNOSIS
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Mrs. L’s shortness of breath is not only severe but markedly worse than baseline. Both of these features should prompt a thorough investigation. Unfortunately, the clinical information does not suggest any of the most common causes of dyspnea (HF, COPD, PE, or pneumonia) (Figure 15-1). Specifically, she has no risk factors for HF (CAD, hypertension, or alcohol abuse), no history of wheezing, or significant smoking history to suggest asthma or COPD, no fever or cough to suggest pneumonia, and no associated symptoms or risk factors to suggest PE (chest pain, cancer, immobilization, prior VTE). She also does not have chest pain that can help limit the differential diagnosis. A careful exam is vital to look for helpful clues.
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On physical exam, the patient appears comfortable at rest but becomes markedly dyspneic with ambulation. Vital signs are BP, 140/70 mm Hg; pulse, 72 bpm; temperature, 37.1°C; RR, 20 breaths per minute. Conjunctiva are pink. Lung exam is clear to percussion and auscultation. There are no crackles or wheezes. Cardiac exam reveals a regular rate and rhythm. S1 and S2 are normal. There is no JVD, S3, S4, or murmur. There is only trace peripheral edema. Abdominal exam is normal. A chest radiograph, ECG, and CBC are normal.
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Despite a thorough exam, the leading diagnosis is unclear as she has none of the pivotal findings (S3, JVD, egophony/bronchial breath sounds, crackles) (Figure 15-1). In such cases, it is particularly important to systematically review the differential diagnosis in order to arrive at the correct diagnosis (Table 15-2). Each item on the list should be reviewed in light of the history and physical to determine whether it remains in the differential and should be explored further, ...