Asthma

What is asthma?

Asthma is a complex clinical syndrome of chronic airway inflammation characterized by recurrent, reversible, airway obstruction. Airway inflammation also leads to airway hyperreactivity, which causes airways to narrow in response to various stimuli.

Asthma is a common chronic condition, affecting approximately 8%-10% of Americans, or an estimated 23 million Americans as of 2008. Asthma remains a leading cause of missed work days. It is responsible for 1.5 million emergency department visits annually and up to 500,000 hospitalizations. Over 3,300 Americans die annually from asthma. Furthermore, as is the case with other allergic conditions, such as eczema (atopic dermatitis), hay fever (allergic rhinitis), and food allergies, the prevalence of asthma appears to be on the rise.


What causes asthma?

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Asthma results from complex interactions between an individual's inherited genetic makeup and their interactions with the environment. The factors that cause a genetically predisposed individual to become asthmatic are poorly understood. The following are risk factors for asthma:

Family history of allergic conditions
Personal history of hay fever (allergic rhinitis)
Viral respiratory illness, such as respiratory syncytial virus (RSV), during childhood
Exposure to cigarette smoke
Obesity
Lower socioeconomic status

The many potential triggers of asthma largely explain the different ways in which asthma can present. In most cases, the disease starts in early childhood from 2-6 years of age. In this age group, the cause of asthma is often linked to exposure to allergens, such as dust mites, tobacco smoke, and viral respiratory infections. In very young children, less than 2 years of age, asthma can be difficult to diagnose with certainty. Wheezing at this age often follows a viral infection and might disappear later, without ever leading to asthma. Asthma, however, can develop again in adulthood. Adult-onset asthma occurs more often in women, mostly middle-aged, and frequently follows a respiratory tract infection. The triggers in this group are usually nonallergic in nature.

Types: allergic (extrinsic) and nonallergic (intrinsic) asthma

Your doctor may refer to asthma as being "extrinsic" or "intrinsic." A better understanding of the nature of asthma can help explain the differences between them. Extrinsic, or allergic asthma, is more common and typically develops in childhood.

Typically, there is a family history of allergies. Additionally, other allergic conditions, such as nasal allergies or eczema, are often also present. Allergic asthma often goes into remission in early adulthood. However, in many cases, the asthma reappears later.

Intrinsic asthma represents a small amount of all cases. It usually develops after the age of 30 and is not typically associated with allergies. Women are more frequently affected and many cases seem to follow a respiratory tract infection. The condition can be difficult to treat and symptoms are often chronic and year-round.

The classic signs and symptoms of asthma are shortness of breath, cough (often worse at night), and wheezing (high-pitched whistling sound produced by turbulent airflow through narrow airways, typically with exhalation). Many patients also report chest tightness. It is important to note that these symptoms are episodic, and individuals with asthma can go long periods of time without any symptoms.

Common triggers for asthmatic symptoms include exposure to allergens (pets, dust mites, cockroach, molds, and pollens), exercise, and viral infections. Tobacco use or exposure to secondhand smoke complicates asthma management.

Many of the symptoms of asthma are nonspecific and can be seen in other conditions as well. Symptoms that might suggest conditions other than asthma include new symptom onset in older age, the presence of associated symptoms (such as chest discomfort, lightheadedness, palpitations, and fatigue), and lack of response to appropriate medications for asthma.



The physical exam in asthma is often completely normal. Occasionally, wheezing is present. In an asthma exacerbation, the respiratory rate increases, the heart rate increases, and the work of respiration increases. Individuals often require accessory muscles to breathe, and breath sounds can be diminished. It is important to note that the blood oxygen level typically remains fairly normal even in the midst of a significant asthma exacerbation. Low blood oxygen level is therefore concerning for impending respiratory failure.


How is asthma diagnosed?

The diagnosis of asthma begins with a detailed history and physical examination. A typical history is an individual with a family history of allergic conditions or a personal history of allergic rhinitis who experiences coughing, wheezing, and difficulty breathing, especially with exercise or during the night. There may also be a propensity toward bronchitis or respiratory infections. In addition to a typical history, improvement with a trial of appropriate medications is very suggestive of asthma.

In addition to the history and exam, the following are diagnostic procedures that can be used to help with the diagnosis of asthma:

Lung function testing with spirometry: This test measures lung function as the patient breathes into a tube. If lung function improves significantly following the administration of a bronchodilator, such as albuterol, this essentially confirms the diagnosis of asthma. It is important to note, however, that normal lung function testing does not rule out the possibility of asthma.

Measurement of exhaled nitric oxide (FeNO): This can be performed by a quick and relatively simple breathing maneuver, similar to spirometry. Elevated levels of exhaled nitric oxide are suggestive of "allergic" inflammation seen in conditions such as asthma.
Skin testing for common aeroallergens: The presence of sensitivities to environmental allergies increases the likelihood of asthma. Of note, skin testing is generally more useful than blood work (in vitro testing) for environmental allergies. Testing for food allergies is not indicated in the diagnosis of asthma.
Other potential but less commonly used tests include provocation testing such as a methacholine challenge, which tests for airway hyperresponsiveness. Hyperresponsiveness is the tendency of the breathing tubes to constrict or narrow in response to irritants. A negative methacholine challenge makes asthma much less likely. Specialists sometimes also measure sputum eosinophils, another marker for "allergic" inflammation seen in asthma. Chest imaging may show hyperinflation, but is often normal in asthma. Tests to rule out other conditions, such as cardiac testing, may also be indicated in certain cases

As per widely used guidelines, the treatment goals for asthma are to:

adequately control symptoms,
minimize the risk of future exacerbations,
maintain normal lung function,
maintain normal activity levels, and
use the least amount of medication possible with the least amount of potential side effects.
Inhaled corticosteroids (ICS) are the most effective anti-inflammatory agents available for the chronic treatment of asthma

decreasing the risk of asthma exacerbations. Furthermore, the combination of a long-acting bronchodilator (LABA) and an ICS has a significant additional beneficial effect on improving asthma control.

The most commonly used asthma medications include the following:

Short-acting bronchodilators (albuterol [Proventil, Ventolin, ProAir, Maxair, Xopenex]) provide quick relief and can be used in conjunction for exercise-induced symptoms.
Inhaled steroids (budesonide [Pulmicort Turbuhaler, Pulmicort Respules], fluticasone [Flonase, Veramyst], beclomethasone [Vanceril, Beconase AQ, QNASL, Quvar], mometasone [Nasonex], ciclesonide [Alvesco]) are first-line anti-inflammatory therapy.
Long-acting bronchodilators (salmeterol [Serevent], formoterol [Foradil]) can be added to ICS as additive therapy. LABAs should never be used alone for the treatment of asthma.
Leukotriene modifiers (montelukast [Singulair], zafirlukast [Accolate]) can also serve as anti-inflammatory agents.
Anticholinergic agents (ipratropium [Atrovent, Atrovent HFA], tiotropium [Spiriva]) can help decrease sputum production.
Anti-IgE treatment (omalizumab [Xolair]) can be used in allergic asthma.
Chromones (cromolyn [Intal, Opticrom, Gastrocrom], nedocromil [Alocril]) stabilize mast cells (allergic cells) but are rarely used in clinical practice.
Theophylline (Respbid, Slo-Bid, Theo-24) also helps with bronchodilation (opening the airways) but again is rarely used in clinical practice due to an unfavorable side-effect profile.
Systemic steroids (prednisone [Deltasone, Liquid Pred], prednisolone [Flo-Pred, Pediapred, Orapred, Orapred ODT], methylprednisolone [Medrol, Depo-Medrol, Solu-Medrol], dexamethasone [DexPak]) are potent anti-inflammatory agents that are routinely used to treat asthma exacerbations but pose numerous unwanted side effects if used repeatedly or chronically.
Numerous other monoclonal antibodies are currently being studied but none are currently commercially available for routine asthma therapy.
There is often concern about potential long-term side effects of inhaled corticosteroids. Numerous studies have repeatedly shown that even long-term use of inhaled corticosteroids has very few if any sustained, clinically significant side effects, including changes in bone health, growth, or weight. However, the goal always remains to treat all individuals with the least amount of medication that is effective. Patients with asthma should be routinely reassessed for any appropriate changes to their medical regimen.

Asthma medications can be administered via inhalers either with or without an AeroChamber or nebulized solution. It is important to note that if an individual has proper technique with an inhaler, the amount of medication deposited in the lungs is no different than that when using a nebulized solution. When prescribing asthma medications, it is essential to provide the appropriate teaching on proper delivery technique.

Smoking cessation and/or minimizing exposure to secondhand smoke are critical when treating asthma. Treating concurrent conditions such as allergic rhinitis and gastroesophageal reflux disease (GERD) may also improve asthma control. Vaccinations such as the annual influenza vaccination are also indicated.

Although the vast majority of individuals with asthma are treated as outpatients, treatment of severe exacerbations can require management in the emergency department or inpatient hospitalization. These individuals typically require use of supplemental oxygen, early administration of systemic steroids, and frequent or even continuous administration of bronchodilators via a nebulized solution. Individuals at high risk for poor asthma outcomes are referred to a specialist (pulmonologist or allergist). The following factors should prompt consideration or referral:

History of ICU admission or multiple hospitalizations for asthma
History of multiple visits to the emergency department for asthma
History of frequent use of systemic steroids for asthma
Ongoing symptoms despite the use of appropriate medication

Patient education is a critical component in the successful management of asthma. An asthma action plan provides an individual with specific directions for daily management of their asthma and for adjusting medications in response to increasing symptoms or decreasing lung function, as usually measured by a peak flow meter.


What is the prognosis for asthma?

The prognosis for asthma is generally favorable. Children experience complete remission more often than adults. Although adults with asthma experience a greater rate of loss in their lung function as compared to age-controlled counterparts, this decline is usually not as severe as seen in other conditions, such as chronic obstructive pulmonary disease (COPD) or emphysema. Asthma in the absence of other comorbidities does not appear to shorten life expectancy. Risk factors for poor prognosis from asthma include

a history of hospitalizations, especially ICU admissions or intubation,
frequent reliance on systemic steroids,
significant medical comorbidities.

Can asthma be prevented?

With the increasing prevalence of asthma, numerous studies have looked for risk factors and ways to potentially prevent asthma. It has been shown that individuals living on farms are protected against wheezing, asthma, and even environmental allergies. The role of air pollution has been questioned in both the increased incidence of asthma and in regards to asthma exacerbations.

Climate change is also being studied as a factor in the increased incidence of asthma. Maternal smoking during pregnancy is a risk factor for asthma and poor outcomes. Tobacco smoke is also a significant risk factor for the development and progression of asthma. The development of asthma is ultimately a complex process influenced by many environmental and genetic factors, and currently there is no proven way to decrease an individual's risk of developing asthma