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Asthma

Etiology
A disease of chronic airway inflammation, bronchial hyperreactivity, and reversible airway obstruction
Due to combination of genetic and environmental factors
It is unclear whether severe RSV bronchiolitis directly causes increased risk of asthma or results from similar pathophysiologic mechanisms; airway hyperreactivity after RSV may persist from months to years
Tobacco exposure has been linked to the development of asthma
Extrinsic (hypersensitivity to allergens) vs. intrinsic (non-immune triggers)
Epidemiology
Affects 5 – 10% of the population
Half of cases have onset before age 10, but can develop at any age
Males > females
Often a family history of asthma or atopic diseases
Mortality has been increasing, perhaps due to overreliance on bronchodilator drugs.
Signs/Symptoms
Signs/symptoms are due to narrowing of intrathoracic airways
Cough
Polyphonic expiratory wheeze
Shortness of breath
Sputum production (mucorrhea)
Sleep disturbance/nocturnal awakenings
Exercise limitation
Expiratory prolongation
Increased AP chest diameter
Hyperinflation of percussion or X – ray
Retractions and accessory muscle use
Tachycardia/tachypnea during episodes.
Treatment
Acute treatment medications
Inhaled short acting b-agonists for bronchodilation
Anticholinergics (e.g., ipratropium bromide)
Oral/IV corticosteriods
Supplemental O2
Prophylactic medications
Long acting b-agonists (salmeterol)
Inhaled cromolyn/nedocromil (mast cell stabilizers)
Oral leukotriene inhibitors
Inhaled corticosteroids should be used for chronic therapy if patient is using bronchodilators > 2X/wk
Avoid aggravating factors (e.g., tobacco exposure, allergic rhinitis, otitis media, sinus infections, GERD)
Appropriate vaccinations, including yearly influenza vaccine
There is little or no role for allergy shots.
Differential Dx
If unresponsive to asthma therapy, consider:
Airway malacia
GERD
Vascular anomalies
Lymphadenopathy
Tumors
Intraluminal masses
Foreign body
Vocal cord bysfunction
If frequent/recurrent infections, consider:
Cystic fibrosis
Immune deficiencies
Primary ciliary dyskinesia.
Diagnosis
History and clinical exam
Reversible airway obstructions measured by spirometry
Peak expiratory flow < 80% predicted
FEV1/FVC < 80%predicted
FEF25-75% < 80% predicted
Demonstration of reversible airway dysfunction
15% increase in FEV1 after b-agonist therapy
Bronchoconstriciton in response to a methacholine or cold air challenge
CXR: Hyperinflation/flattened diaphragms, atelectasis
ABG: Respiratory alkalosis in mild exacerbations; hypoxemia and metabolic acidosis in severe disease
Sputum culture: increased eosinophils; possible secondary infection.
See National Heart Lung and Blood Institute guidelines for severity scoring.
Prognosis/Clinical Course
Episodic course with acute exacerbations separated by symptom-free periods
Severity/response to treatment is followed by measuring PEFR (peak expiratory flow rate)
Prognosis ranges from minimal symptoms to significant morbidity/mortality.
Prognostic factors: Severity of asthma, adherence to therapy, level of control, and co-morbidities (allergies, sinus disease, recurrent/chronic otitis media, obesity, GERD, airway malacia/stenosis)
Likelihood of “growing out of asthma” may depend on severity, compliance, and exposure to triggers
Status asthmaticus: Prolonged, severe attack that does not respond to initial therapy; may lead to respiratory failure and death