2016 Section 5 Green Book

Comorbidities of asthma and the unified airway

FIGURE 1. (A) Bronchial airway: asthma. (B) Chronic rhinosinusitis: sinonasal epithelium. Note the similarities and the chronic inflammatory infiltrates with increased numbers of eosinophils in both A and B. Note the remodeling and narrowing of the airway in A.

associated with subjective and objective improvements in asthma. 24,32

childhood. 45 Other factors including prematurity, air pol- lution, and atopy help to contribute to the development of asthma.

Epidemiologic relationships AR has a prevalence of between 15% and 40%. 33,34 Asthma affects 7% to 8% of the population. 33,34 Between 75% and 80% of atopic and nonatopic people with asthma have rhinitis. Rhinitis is also a risk factor for developing asthma. 35 In children aged 6 to 11 years the male to female ratio of asthma is 3:2 for affected individuals. Older chil- dren (aged 12 to 17 years) have a male to female ratio of 8:5. 36 It is theorized that males have smaller airways for a given lung size than females. 37 The smaller airways may predispose males to more wheezing and lower respiratory illnesses. As the males grow older, the ratio normalizes then reverses later in life, resulting in a larger female component. The development of atopy in early childhood, before 6 years of age, is a risk factor for increased bronchial hy- perresponsiveness in late childhood. 37 The presence of AR predisposes one to a greater risk of bronchial hyperactivity even before asthma is diagnosed. Eleven percent (11%) to 32% of patients who have seasonal AR will have bronchial hyperresponsiveness with a methacholine challenge outside of their allergic season. During the season, 48% will have a positive methacholine challenge test. 38 About 50% of patients with perennial AR without asthma showed hyper- responsiveness to bronchial challenge. Only 25% of sensi- tized individuals sensitized to 1 or more allergens go on to develop asthma. 39 Linneberg et al. 40 showed that sensitiv- ity to perennial allergens significantly increases one’s risk of developing asthma compared to those sensitized to sea- sonal allergens. Seasonal AR patients had a 10-fold greater risk of developing asthma, compared to a 50-fold increase in risk for those who have perennial allergies. 41 Certain risk factors have been noted for the development of asthma. Tobacco exposure is a significant risk factor in the development of asthma in children 42 and the mor- bidity of asthma in adults. 43 Obesity is a risk factor for development of and the expression of asthma. 44 Recur- rent viral throat infections, ie, respiratory syncytial virus (RSV), increases a child’s risk of developing asthma later in

Morbidity and mortality There were 13.9 million outpatient visits for asthma in 2002. Most visits were in children under the age of 18 years (687 per 10,000) compared to those older than 18 years (181 per 10,000). 36 The utilization of emergency room (ER) services is increasing over time. Unscheduled visits to the ER increased to 1.9 million in 2002. Children under the age of 4 years were most affected. African American children were 4 times as likely as Caucasian children to go to the ER for their asthma. Hospitalizations for asthma increased 200% in children and 50% in adults from 1960 to 1980. 45 The cost of asthma continues to climb over time. Per person costs per year for asthmatics are $1300. Asthma-related costs have risen over 50% from 1984 to 1994. The direct and indirect costs in the United States were $12 billion. Only 10% to 20% of patients have severe asthma, which accounts for 50% of the total cost of treatment rendered to this population. Fortunately, asthma deaths are rare under the age of 15 years. The 1978 mortality rate from asthma was 0.8/100,000, and increased to 2.0/100,000 in 1989. It went up to 2.1/100,000 in 1994. A drop in the year 2000, to 1.6/10,000, was noted. The 2002 mortality rate for asthma was noted to be 1.5 per 100,000. The African American mortality rate is 200% higher than the rate in Caucasian children at 3.7 per 100,000. 36 Clearly some racial disparity exists between the patients afflicted with this disease.

Pathophysiology There are 2 key mechanisms that are proposed to explain the pathophysiology of asthma: inflammatory mechanisms, which include local reactions and distal crosstalk in the airway; and systemic, neurogenic mechanisms.

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