Asthma
last authored: Dec 2012, David LaPierre
last reviewed:
Introduction
Asthma is a chronic inflammatory disorder of the airways, causing recurrent episodes of wheezing, breathlessness, chest tightness, and cough. It usually is associated with airway hyperresponsiveness.
Incidence is highest in children, in whom it is the most common chronic disease in developed countries. Up to 7% of the US is thought to have asthma.
Asthma can be life-threatening. Mortality can be reduced dramatically with effective medication and lifestyle prevention, but there are still 300-500 deaths per year in Canada.
Medication adherence is very important, and also very challenging. Unfortunately, both patients and health care professionals frequently do not work together to ensure maximal treatment.
The Case of...
a simple case introducing clincial presentation and calling for a differential diagnosis to get students thinking.
Causes and Risk Factors
Cause of asthma remains unknown, but appears polygenic and multifactorial. Episodes usually in paroxysms, usually associated with a trigger.
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.
Symptoms can also be triggered by cold air or exercise.
Infections, such as viral respiratory tract infections can cause bronchospasm, even without a diagnosis of asthma. As a result, they can cause significant exacerbations of asthma.
Genetic factors include polymorphisms in the beta-adrenergic receptor gene. This leads to diminished beta-agonist responsiveness regarding medication.
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.
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.
Signs and Symptoms
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.
All that wheezes is not asthma.
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
History
Symptoms that suggest asthma include:
- worsen with triggers, ie allergens, irritants, or infection
- most severe at night or in the early morning
- episodic attacks of severe dyspnea, coughing, wheezing, and chest tightness
- responsiveness to medication
- worsening with laughing or playing
Paroxysmal nocturnal dyspnea can also be caused by asthma, thought to be due to decreased vital capacity, decreased body temperature, decreased endogenous vasodilators 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.
Other flags to watch for include:
- absenteeism from school
- 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.
Past medical history
- seasonal allergies
- excema
Family history
- asthma (how severe?)
- eczema
- allergies
Follow-up visits
As medications and lifestyle is optimized, ask about the following:
Symptoms and activities
daytime symptoms |
<4 days/week |
nighttime symptoms |
<1 day/week |
physical activity |
normal |
medications
- what patient is taking
- frequency of rescue medication use
- technique
- adherence to plan
absenteeism
enviromental changes and triggers, stressors
complicating problems and alternative diagnoses
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
Differential Diagnosis
Asthma cannot be diagnosed at first presentation. Instead, it is called reactive airway disease until a pattern is established.
Other diseases that could be confused for asthma include:
- bronchiolitis
- pneumonia
- reflux
- croup, epiglottitis (more stridor)
- foreign body
- cystic fibrosis
- vascular ring
- pertussis
- tuberculosis
- Churg-Strauss vasculitis
- allergic pulmonary aspergillosis
- immunodeficiencies
- bronchiectasis
Asthma Control
Control of inflammation and bronchodilation are both crucial to controlling asthma.
- targets for
control - patient
education - medical
management - children
- acute
attacks - reasons for
poor control
Targets for Control
Canada's guidelines are a bit more liberal than world standards.
Good control is:
- symptoms less than 4 times weekly
- not waking up at night
- normal activity levels
- maintain PFTs as close to normal as possible
- prevent exacerbations
- avoiding adverse effects of asthma meds
- decrease asthma mortality
Most patients and physicians think asthma is under control, but according to criteria, over 50% of patients are not (ref).
Consequences and Course
Asthma can range from mild to life-threatening. Consequences of poor control can lead to
- reduced function, for exercise and daily activities
- increased severity of infections
- multiple hospital visits and admissions, including to the intensive care unit
- death
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.
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