Priority Topic: Asthma

Key Feature 1a: In patients of all ages with respiratory symptoms (acute, chronic, recurrent): Include asthma in the differential diagnosis.
Skill: Clinical Reasoning
Phase: Hypothesis generation, Diagnosis

Key Feature 1b: In patients of all ages with respiratory symptoms (acute, chronic, recurrent): Confirm the diagnosis of asthma by appropriate use of:

1. History
   
2. Physical examination
   
3. Spirometry

Skill: Clinical Reasoning
Phase: History, Physical

My differential diagnosis to a patient who presents with dyspnea is as follows:

1. Cardiac causes 
   
   1. Myocardial dysfunction (ex: ischemic cardiomyopathy) 
      
   2. Valvular heart disease 
      
   3. Pericardial disease (ex: tamponade) 
      
   4. Increased cardiac output (ex: anemia) 
      
   5. Arrhythmia 
      
2. Pulmonary causes 
   1. Upper airway (ex: foreign body, anaphylaxis) 
      
   2. Chest wall and pleura (ex: pleural effusion) 
      
   3. Lower airway (ex: asthma, chronic obstructive pulmonary disease) 
      
   4. Alveolar (ex: pneumonia) 
3. Central causes (ex: metabolic acidosis, anxiety) 

To look for or rule out asthma, consider the illness script for asthma as follows:

History
Asthma characteristically presents as recurrent episodes of dyspnea and wheeze, with precipitants that include exercise, cold, and respiratory allergens (ex: animal dander, smoke). These patients are more likely to have a personal or family history of atopic dermatitis and allergic rhinitis, and they are likely to have family members with a history of asthma. Asthma usually presents in childhood, although presenting in adulthood is possible. Sometimes patients may have been previously given a trial of an inhaler (ex: salbutamol), and if the patient responded well, this may increase your suspicion of asthma.

Physical examination
During an acute exacerbation of asthma, the typical presentation is a diffuse musical wheeze on auscultation of the lung fields. The patient may also have respiratory distress if moderate to severe. Because of the obstructive physiology of asthma, during an acute exacerbation you would also expect a prolonged expiratory time that more closely matches the inspiratory time. Patients may have undiagnosed atopic dermatitis; the presence of associated findings on examination may increase your suspicion of asthma. 

Spirometry
If you suspect asthma based on your clinical assessment, the next step is to send the patient for spirometry testing, pre- and post-bronchodilator therapy. If a patient shows significant reversible airflow limitation (with an increase in FEV1 of more than 12 percent from the baseline measurement, following administration of 2 to 4 puffs of a quick-acting bronchodilator), this is diagnostic for asthma. If the patient did not meet the 12% improvement in FEV1 criterion, and your clinical suspicion remains high, consider sending for bronchoprovocation testing. If this is positive, then they have a diagnosis of asthma regardless of degree of reversible airflow limitation on spirometry.