Asthma, Definition, Background, Pathogenesis, Classification



Asthma can be defined as a chronic disease that affects the air passages, common in all ages and considered as one of the most common chronic diseases of children. The prevalence of asthma in children ranges between 10-15%. The aetiology is poorly understood as it is a complex disorder involving immunological, infectious, biochemical, genetic, and psychological factors. According to Global Alliance against Chronic Respiratory Diseases, in the year 2010, one billion people worldwide had chronic lung diseases of which 300 million were affected with asthma.

Asthma Background

The Global Initiative for Asthma Management (GINA, 2013) considers asthma as a serious worldwide health problem. This chronic disease, which affects the airways of individuals of different ages, becomes a server burden to deal with on a daily basis, raises health care costs, and sometimes increases fatality in case it is uncontrolled. An intervention is critical to provide the needed assistance to all stakeholders (individuals, families, communities, and healthcare providers) for efficiently managing and limiting the effects of asthma.

Asthma accounts for $6.2 billion worth of treatment costs. Approximately 1.81 million people each year (47.8% of individuals aged 18 years or younger) require treatment in the emergency department. Asthma is the main reason for missing up to 10 million school days among children and adolescents whose age range between 5-17 years old.

The aetiology of asthma is not fully understood, but several factors have an impact on the development and prognosis. The risk factors for asthma can be divided into host factors (genetic factors, gender, obesity) and environmental factors (allergens, infections, occupational sensitizers, outdoor/ indoor air pollution, diet). The mechanisms whereby these factors influence the development of asthma are complex.

Defining Asthma

The National Heart Lung and Blood Institute defines asthma as a chronic lung disease that inflames and narrows the airways. During an attack, the lining of the passages swells, causing the airways to narrow and reduces the air flow in and out of the lungs.

Individuals who are at risk of asthma inflammation suffer from recurrent episodes of wheezing, coughing, chest tightness, breathlessness, and that mostly take place at night or early morning hours. The cause of these episodes can be a partial or a total airflow obstruction which can be “often reversible either spontaneously or with treatment. The inflammation also causes an associated increase in the existing bronchial hyperresponsiveness to a variety of stimuli”.

Even though there are advances and recent progress in research related to asthma treatments and pathogenesis, this chronic disease is considered as one of the rising allergic diseases in terms of its incidence and recurrence. According to the NHLBI, Asthma is considered to be a major health concern due to the rising incidences of this chronic illness throughout the country. The exposure to a variety of environmental factors can trigger and intensify the illness. The American Academy of Pediatrics calls for adopting the practice of asthma management by avoiding environmental allergens and irritants.

Pathogenesis of Asthma

The airway obstruction in asthma is initiated by inflammation and muscle spasm that is mostly reversible. It is generally believed that both genetic and environmental factors, as well as the allergens, are important in the initiation and continuation of the airway inflammation. Common precipitating allergens underlie asthma pathogenesis reported by the National Heart, Lung and Blood Institute. These allergens include tobacco smoke, dust mites, animal fur, cockroaches, pollens, molds, other airborne irritants including acrylic and other aerosolized dental materials, viral respiratory infections and diet. Additional triggers leading to asthma exacerbations include wood smoke, physical activity, cold air, food additives, aspirin, emotional upset and stress such as anger and crying.

Classification of asthma

Classification of asthma according to severity of clinical features based on the guidelines of the Global Initiative for Asthma (GINA): (Tab.1)

Classification of asthma

Prevalence of asthma symptoms in children

Asthma is the most common chronic illness of childhood. During the last decades of the twentieth century, the spread to asthma has been widening around the world. The prevalence is constantly increasing in industrialized countries throughout the world .Some of the studies reported that the disease affects approximately 3 – 5% of the adult population and as much as 10% of children. Reasons behind the asthma prevalence are under epidemiology investigation worldwide.

The International Study of Asthma and Allergies in Childhood (ISAAC), which was conducted in different locations recruiting over 700.000 children, investigated asthma prevalence and concluded that asthma symptom prevalence was strikingly different around the world. Even though asthma prevalence is greater among minority groups, i.e. black children attribute by 5-8% while Hispanics children attribute by 15%, other findings indicate that recent increase in the prevalence was among white children. The death rate among blacks is consistently higher than whites.

Before puberty, the prevalence of asthma among boys is triple the number among girls. During adolescence, the prevalence value is equal across gender. Meanwhile, adult-onset asthma is more common in women than in men.

In most children, asthma develops before age five years, and, in more than half, asthma develops before age three years. The global prevalence of recent wheeze (≤ 12 months) was 11.1% amongst children aged 6-7 years and 13.2% amongst children aged 13-14 years. To observe trends in time, prevalence has been re-assessed recently with an interval of 5-10 years. Although there was little change in the overall global prevalence of current wheeze, international differences in asthma symptom prevalence have been reduced, particularly in the 13-14 year age group.

Severity and control of asthma

Asthma severity can be classified into four distinct categories varying from mild intermittent to severe persistent asthma. Another concept, which is related to yet different from asthma severity, is widely used. Asthma control reflects current functioning and may change markedly over relatively short periods of time, whereas asthma severity is a relatively stable characteristic of the individual that may change slowly over time. Control of asthma also refers to the reduction of the clinical manifestation of asthma achieved with treatment and reflects the adequacy of treatment.

Asthma control refers to the control of the clinical manifestations of the disease and is the ultimate goal of asthma management. The underlying severity of asthma in a patient may be modified by changes in the environment and by the treatment received for asthma. The undertaken changes will eventually have an effect on the patient’s symptoms and their ability to function. Asthma control reflects the combined effect of underlying disease severity, environmental exposures and the effectiveness of treatment.

A number of patient-related variables may influence asthma control. It is identified several independent patient-related determinants of inadequate asthma control, including female gender and overweight status. Control also varied according to the type of asthma supervision. Patients supervised exclusively by specialists (rather than GPs) were more likely to have their asthma properly controlled.

Patients who were dispensed combined long-acting beta-2 agonist (LABA) and inhaled corticosteroids (ICS) therapy was also more likely to have their symptoms properly controlled, particularly at higher doses. The Australian National Asthma Council (NAC) recommends the day-to-day management of asthma, including adjustment of medications, should closely depend on an ongoing assessment of asthma control.


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