We define asthma to identify the disease correctly and to differentiate it from other diseases. To fulfill this goal, definition of asthma has been changing over last 40 years. The clinician, physiologist, immunologist, pathologist or epidemiologist - all view asthma from different perspectives.
In 1997, Expert Panel-2 of National Asthma Education and Prevention Program, USA formulated a working definition of asthma. In 2002, the Expert Panel-3 discussed extensively and adopted the same definition, which is as follows:Asthma is a chronic inflammatory disorder of the airways:
• Here many cells and cellular elements play a role: in particular, mast cells, eosinophils, T lymphocytes, macrophages, neutrophils and epithelial cells.
• In susceptible individuals, this inflammation causes recurrent episodes of wheezing, breathlessness, chest tightness and coughing, particularly at night or in the early morning.
• These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment.
• The inflammation also causes an associated increase in the existing bronchial hyper-responsiveness to a variety of stimuli.
• Moreover recent evidence indicates that sub-basement membrane fibrosis may occur in some patients with asthma and that these changes contribute to persistent abnormalities in lung function.
This definition focuses on five components:
- Nature of disease
- Cardinal features
- Reversible obstruction in pulmonary function testing
- Hyper responsiveness to multiple stimuli
- Cause of persistent asthma
This definition is to some extent a complete one. The critical role of inflammation in asthma is so important that it is described in the first component of the definition. We can summarize this definition in a simple form:
Asthma is a chronic inflammatory disorder causing hyper-responsiveness of airways to certain stimuli resulting in recurrent variable airflow limitation, at least partly reversible, presenting as wheezing, breathlessness, chest tightness and coughing.