Asthma

Essentials of Diagnosis

• Episodic or chronic symptoms of wheezing, dyspnea, or cough

• Symptoms frequently worse at night or in the early morning

• Prolonged expiration and diffuse wheezes on physical examination

• Limitation of airflow on pulmonary function testing or positive bronchoprovocation challenge

• Reversibility of airflow obstruction, either spontaneously or following bronchodilator therapy

General Considerations

• Characterized by variable airway obstruction, airway hyperresponsiveness, and airway inflammation

• No single histopathologic feature is pathognomonic but common findings include

  • Airway inflammatory cell infiltration with eosinophils, neutrophils, and lymphocytes (especially T cells)

  • Goblet cell hyperplasia, sometimes plugging of small airways with mucus

  • Collagen deposition beneath the basement membrane

  • Hypertrophy of bronchial smooth muscle

  • Airway edema

  • Mast cell activation

  • Denudation of airway epithelium

Demographics

• Affects approximately 8–10% of the population

• Each year, approximately 10 million office visits, 1.8 million emergency department visits, and more than 3500 deaths in the United States are attributed to asthma

Symptoms and Signs

• Characterized by

  • Episodic wheezing

  • Shortness of breath

  • Chest tightness

  • Cough

• Symptoms vary over time, vary in intensity, and are often worse at night or in the early morning

Differential Diagnosis

• Upper airway disorders

  • Vocal fold paralysis, vocal fold dysfunction syndrome

  • Narrowing of the supraglottic airway

  • Laryngeal masses or dysfunction

• Lower airway disorders

  • Foreign body aspiration

  • Tracheal masses or narrowing, tracheobronchomalacia

  • Airway edema (eg, angioedema or inhalation injury)

  • Nonasthmatic chronic obstructive pulmonary disease (COPD)

  • Bronchiectasis

  • Allergic bronchopulmonary mycosis

  • Sarcoidosis

  • Cystic fibrosis

  • Eosinophilic pneumonia

  • Hypersensitivity pneumonitis

  • Bronchiolitis obliterans

• Systemic vasculitis with pulmonary involvement, such as eosinophilic granulomatosis with polyangitis

• Cardiac disorders (heart failure, pulmonary hypertension)

• Psychiatric causes include conversion disorders ("functional" asthma) and emotional laryngeal wheezing or episodic laryngeal dyskinesis

Laboratory Findings

• Arterial blood gas measurements may be normal during a mild exacerbation

• However, respiratory alkalosis and an increase in the alveolar-arterial oxygen difference (A–a–DO₂) are common

• During severe exacerbations, hypoxemia develops and the PaCO₂ returns to normal

• The combination of an increased PaCO₂ and respiratory acidosis may indicate impending respiratory failure and the need for mechanical ventilation

Pulmonary function testing

• Spirometry helps determine the presence and extent of airflow obstruction and whether it is immediately reversible

• Bronchial provocation testing may be useful when asthma is suspected but spirometry is nondiagnostic

• Peak expiratory flow (PEF) meters can

  • Establish peak flow variability

  • Quantify asthma severity

  • Provide both patient and clinician objective measurements on which to base treatment decisions

Imaging

• Chest radiographs

  • Usually normal or show only hyperinflation

  • Other findings may include bronchial wall thickening and diminished peripheral lung vascular shadows

• See Tables 9–3, 9–4, and 9–2

Mild to moderate exacerbations

• Many patients respond quickly and completely to an inhaled short-acting beta-agonist (SABA) alone

• However, an inhaled SABA may need to be continued at increased doses, eg, every 3–4 hours for 24–48 hours

• Patients may also require a short-term increase in inhaled corticosteroids to four times the usual dose

• In patients not improving after 48 hours, a 5- to 7-day course of oral corticosteroids (eg, prednisone 0.5–1.0 mg/kg/day) may be necessary

Severe exacerbations

• All patients with a severe exacerbation should immediately receive oxygen, high doses of an inhaled SABA, and systemic corticosteroids

• Intravenous magnesium sulfate

  • Is not recommended for routine use in asthma exacerbations

  • However, a 2-g infusion over 20 minutes may reduce hospitalization rates in acute severe asthma (forced expiratory volume in 1 second [FEV₁] < 25% of predicted on presentation or failure of initial treatment)

Follow-Up

• All patients should be provided with

  • Necessary medications and education in how to use them

  • Instruction in self-assessment

  • Follow-up appointment

  • An action plan for managing recurrence

Complications

• Exhaustion, dehydration

• Airway infection

• Tussive syncope

• Acute hypercapnic and hypoxemic respiratory failure (severe disease)

• Pneumothorax (rare)

When to Refer

• Atypical presentation or uncertain diagnosis of asthma, particularly if additional diagnostic testing is required

• Complicating comorbid problems, such as rhinosinusitis, tobacco use, multiple environmental allergies, suspected allergic bronchopulmonary mycosis

• Occupational asthma

• Uncontrolled symptoms despite a moderate-dose inhaled corticosteroid and a long-actomg beta-agonist

• Patient not meeting goals of asthma therapy after 3–6 months of treatment

• Frequent asthma-related healthcare utilization

• More than two courses of oral prednisone therapy in the past 12 months

• Any life-threatening asthma exacerbation or exacerbation requiring hospitalization in the past 12 months

• Presence of social or psychological issues interfering with asthma management