Asthma

 

Asthma is a chronic inflammatory disorder of the airways, causing recurrent episodes of wheezing, breathlessness, chest tightness, and cough occurring in paroxysms, usually associated with a trigger. It usually is associated with airway hyperresponsiveness.

Incidence is highest in children, in whom it is the most common chronic disease. Up to 7% of the US is thought to have asthma.

Mortality has gone down by 50% over the last few years, but there are still 500 deaths per year in Canada.

 

 

Causes and Risk Factors

Cause of asthma remains unknown, but appears polygenic and multifactorial.

 

Enviromental allergens include air pollution, passive smoking, molds, dust mites, cockroaches, pets, and other agents. The eradication of mold and increased home ventilation can improve asthma symptoms and reduce medication use (Burr et al, 2007).

Occupational exposures are also very important.

 

Infections, such as viruses can cause bronchospasm, even without a diagnosis of asthma.

 

Genetic factors include beta-adrenergic receptor, leading to diminished beta-agonist responsiveness.

 

Atopy is strongly linked to asthma, and between 30%-80% of people with asthma also have allergic rhinitis and/or eczema (atopic dermatitis).

 

Obesity also appears linked to higher rates of asthma. Diet can also be important.

Symptoms can be triggered by cold air, exercise or exposure to allergens, and are often worse at night or in early morning.

 

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Signs, Symptoms, and Diagnosis

 

Asthma has a wide spectrum of predisposing factors and clinical presentations, making uniform classification difficult. One set of categories includes intermittent, persistently mild, persistently moderate, and severe persistent asthma, based on frequency and severity. Interference with activity, nighttime symptoms.

 

Typically, asthma is divided into extrinsic asthma, initiated by a type I hypersensitivity to atopic, occupational, or other extrinsic antigens, and intrinsic asthma, initiated by nonimmune mechanisms, including aspirin, pulmonary infections, stress, cold, and exercise.

Diagnosis requires documentation of hyperactivity and reversibility of airflow limitation, either by history or with spirometry.

  • history
  • physical exam
  • pulmonary function testing
  • differential diagnosis

History

 

Diagnosing Asthma

Classical symptoms of

Asthma classically leads to episodic attacks of severe dyspnea, coughing, and wheezing. Chest tightness may also be present.

 

 

PND can also be caused by asthma, thought to be due to decreased vital capacity, decreased body temperature, decreased endogenous vasodilators (what?) and increased exposure to bed allergens.

 

Exercise-induced asthma can cause dyspnea greater than expected with exertion, with symptoms worst 15-30 minutes after exercise cessation.

Absenteeism from school

Nighttime symptoms

Encounters with health care providers (GP, ED, admissions, ICU)

 

 

Attacks can last up to several hours, but in some people, asthma can persist at low levels all the time. Many people are asymptomatic between attacks.

 

Hemoptysis suggests Churg-Strauss vasculitis, allergic pulmonary aspergillosis, or bronchiectasis.

 

On follow-up visits, important questions include:

 

medications

  • what patient is taking
  • frequency of rescue medication use
  • technique
  • adherence to plan

activity

absenteeism

enviromental changes and triggers, stressors

complicating problems and alternative diagnoses

 

 

Pathophysiology

Asthma is an obstructive disease associated with widespread but variable bronchoconstriction and airflow limitation. This is due to hyperresponsiveness to a variety of stimuli which normally would have little or no effect.

 

Antigenic stimulation causes mast cell degranulation and leukocyte activation, resulting in inflammation. Eosinophils, mast cells, macrophages, T cells, neutrophils, and epithelial cells are all involved.

 

TH2 CD4+ cells are prominent in the asthmatic mielieu, secreting IL-4 and other cytokines promoting allergic inflammation and stimulating B cell production of IgE and other antibodies. There is evidence that deregulation of TH2 inhibition by interferon-gamma, and downregulation of the transcription factor T-bet, may be important.

 

Chronic airway remodeling also occurs with poorly managed asthma. Bronchial smooth muscle hyperplasia and hypertrophy and deposition of collagen, potentially mediated by mast cell release of growth factors and proteases, can increase the constrictive effects of inflammation.

 

Mucus collects in airways, and lungs become overinflated with mucus plugs. Goblet cell metaplasia and hypertrophy of bronchial musculature and submucosal mucus glands occurs due to increased function. The basement membranes can also thicken.

 

Chronic asthma can lead to irreversible airflow limitation, rendering bronchodilators less efficient.

 

Hypersecretory- and cough-variant asthma.

 

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Asthma Control

Control of inflammation and bronchodilation are both crucial to controlling asthma.

 

  • control targets
  • medical management
  • exercise-induced asthma
  • acute attacks
  • patient education
  • reasons for poor control

Medical Management

 

  • Mild intermittent: salbutamol, as needed
  • Mild persistent: inhaled corticosteroids (fluticasone/beclomethasone) + salbutamol PRN
  • Moderate persistent: fluticasone + salmeterol + salbutamol PRN
  • Severe persistent: fluticasone + salmeterol + oral prednisone + salbutamol PRN

 

Alternatives include ipratroprium, monoleukast, theophylline, and cromolyn sodium

Do not use LABA alone, as this increases mortality.

Ciclesonide (Alvesco)

  • given once a day
  • inert until it contacts respiratory epithelium esterases, so prevents oral thrush

A tubuhaler/discus can be beneficial for people reluctant to use MDIs.

 

Steroid-resistant asthma

Steroid-resistant asthma patients appear to produce higher levels of GRĪ², a dominant-negative corticosteriod receptor, leading to a loss of effect with administered steriods.

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Resources and References

 

Burr ML et al. 2007. Effects on patients with asthma of eradicating visible indoor mould: a randomised controlled trial. Thorax. 62(9):767-72.

 

Thomas M et al. 2009. Breathing exercises for asthma: a randomised controlled trial. Thorax. 64(1):55-61.