Asthma

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Basics

Description

  • A heterogeneous disease characterized as chronic inflammation of the airway; patients present with history of wheeze, shortness of breath (SOB), chest tightness, and cough which varies in time and intensity along with variable expiratory flow (1).
  • Common triggers: exercise, allergen-irritant exposure, change in weather, laughter, or viral respiratory infections
  • Patient may experience symptoms-free periods alternating with sporadic flare-up (exacerbations).
  • Most common asthma phenotypes (1):
    • Allergic asthma: usually present since childhood and has strong family history of allergic diseases
    • Nonallergic asthma
    • Late-onset asthma: more common in females
    • Asthma with fixed airflow limitation: due to airway remodeling
    • Asthma with obesity
  • Four major classifications of asthma severity used primarily to initiate therapy (2):
    • Intermittent: symptoms ≤2 days/week, nighttime awakenings ≤2 times per month, short-acting β-agonist (SABA) use ≤2 days/week, no interference with normal activity, and normal forced expiratory volume in 1 second (FEV1) between exacerbations with FEV1 (predicted) >80% and FEV1/forced vital capacity (FVC) normal for age
    • Mild persistent: symptoms >2 days/week but not daily, nighttime awakenings 3 to 4 times per month, SABA use >2 days/week but not daily, minor limitations in normal activity, and FEV1 (predicted) >80% and FEV1/FVC normal for age
    • Moderate persistent: daily symptoms, nighttime awakenings >1 times per week but not nightly, daily use of SABA, some limitation in normal activity, and FEV1 (predicted) 60–80% and FEV1/FVC reduced 5% for age
    • Severe persistent: symptoms throughout the day, nighttime awakenings often 7 times per week, SABA use several times a day, extremely limited normal activity, and FEV1 (predicted) <60% and FEV1/FVC reduced >5% for age

Epidemiology

Prevalence

Asthma affects 235 million individuals worldwide.

  • 383,000 deaths worldwide reported in 2015
  • Asthma affects about 10% of children ages 5 to 18 years in the United States.
  • Asthma prevalence is greater in boys than girls; however, in adults, women are more affected.
  • Obesity is associated with increased prevalence and incidence of asthma, especially in women with abdominal obesity.

Etiology and Pathophysiology

Airway hyperreaction begins with inflammatory cell infiltration and degranulation, subbasement fibrosis, mucus hypersecretion, epithelial injury, significant smooth muscle hypertrophy and hyperreactivity, angiogenesis that then leads to intermittent airflow obstruction due to reversible bronchospasm (3).

Genetics
  • Genetic association with increased interleukin (IL) production and airway hyperresponsiveness leading to asthma; genome-wide association studies (GWAS) show genetic predisposition leading to increased production of IgE, which increased chances of developing the disease (1).
  • Variations in genetic coding have been linked to different levels of response to treatment, which is a key factor for controlling the disease and decreasing rates of exacerbation (1).

Risk Factors

  • Host factors: genetic predisposition, sex, race, obesity, preterm or small for gestational age (SGA)
  • Environmental: viral infections, animal and airborne allergens, tobacco smoke exposure, pollution, stress
  • Aspirin or NSAIDs hypersensitivity or β-blockers
  • Persons with food allergies and asthma are at increased risk for fatal anaphylaxis from those foods (1,2).

Commonly Associated Conditions

  • Atopy: eczema, allergic conjunctivitis, allergic rhinitis
  • Obesity (associated with higher asthma rates)
  • Sinusitis
  • Gastroesophageal reflux disease (GERD)
  • Obstructive sleep apnea (OSA)
  • Depression

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