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PATIENT 
Mr. C is a 32-year-old man with occasional wheezing.
What is the differential diagnosis of wheezing? How would you frame the differential?
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CONSTRUCTING A DIFFERENTIAL DIAGNOSIS
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Wheezing and stridor are symptoms of airflow obstruction caused by the vibration of the walls of pathologically narrow airways. Wheezing is a musical sound produced primarily during expiration by airways of any size. Stridor is a single pitch, inspiratory sound that is produced by large airways with severe narrowing; it may be caused by severe obstruction of any proximal airway (see A through D in the differential diagnosis outline below).
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Stridor is often a sign of impending airway obstruction and should be considered an emergency.
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Distinguishing between wheezing and stridor is essential. Typically, patients with either wheezing or stridor describe their symptoms simply as wheezing. The physical exam will determine whether the patient actually has wheezing or stridor. Because the differential diagnosis for airway obstruction is extensive, an anatomic approach is helpful.
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Stridor
Nasopharynx and oropharynx
Tonsillar hypertrophyb.
Pharyngitisc.
Peritonsillar abscessd.
Retropharyngeal abscess
Laryngopharynx and larynx
Epiglottitisb.
Paradoxical vocal cord movement (PVCM)
Anaphylaxis and laryngeal edemad.
Postnasal dripe.
Benign and malignant tumors of the larynx and upper airwayf.
Vocal cord paralysis
Trachea
Tracheal stenosis
Tracheomalacia
Goiter
Proximal airways
Foreign-body aspiration
Wheezing
Proximal airways: Bronchitis
Distal airways
Asthma
Chronic obstructive pulmonary disease (COPD)
Pulmonary edema
Pulmonary embolism
Bronchiectasis
Bronchiolitis
Heart failure
Sarcoid
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Mr. C has been having symptoms for 1–2 years. His symptoms have always been so mild that he has never sought care. Over the last month, he has been more symptomatic with wheezing, chest tightness, and shortness of breath. His symptoms are worse with exercise and worse at night. He notes that he often goes days without symptoms.
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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The presence of wheezing, chest tightness, and shortness of breath are pivotal clues that place asthma at the top of the differential diagnosis. Although asthma is by far the most likely diagnosis, other diseases that could account for recurrent symptoms of airway obstruction should be considered (Table 33-1). Allergic rhinitis can cause cough and wheezing, but it would be very unusual for it to cause shortness of breath. Vocal cord dysfunction, such as PVCM, is frequently confused with asthma and can cause recurrent stridor. COPD can also cause chronic wheezing and pulmonary symptoms (Figure 33-1).
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