Bronchial asthma is a common disease affecting 10-20% of the population. In the vast majority of cases the disease is mild and often unrecognized. There is evidence that the prevalence of asthma is increasing the reason for this being unknown. In spite of better understanding of the pathophysiological process involved in this disease, which has led to apparently improved treatment, mortality from asthma has not been influenced and in some countries has increased. It is of two major types-
1) Early onset asthma
2) Late onset asthma
Contrasting Features of the two major types of Asthma
| Feature | Extrinsic Asthma | Intrinsic Asthma |
| Age at onset | in childhood | Adult |
| Personal/family history | commonly present | Absent |
| Preceding allergic illness | Present | Absent |
| Allergens | Present | None |
| Drug Hypersensitivity | None | Present |
| Serum IgE levels | Elevated | Normal |
causes
Early onset asthma
Early onset asthma (atopic) it is common for asthma to have its onset in childhood and generally it occurs in atopic individuals who readily form IgE antibodies to commonly encountered allergens. Asthma is these individuals are after referred to as 'atopic' asthma.
The allergens responsible for asthma in atopic individuals generally enter the bronchi with inspired air and are derived from organic material such as pollen mite containing house dust, feathers, animal dander and fungal spores. This causes the release, from cells, such as the mast cell, in the bronchial wall of pharmacologically active substances which provoke bronchial construction and an inflammatory reaction of allergic type in the bronchial wall.
The mast cell does not play such a major role as once thought but eosinophils plays an important role, the asthamatic inflammatory reaction being characterized by a cellular infiltraction rich in activated corinophis. There cells release several mediactors including lipid mediators and oxygen radicals and their granules also contain basic protein including major basic protein rasinophil cationic protein, lasiophil derived neurotoxin and easionphil perovidase. T lymphocytes are present in increased numbers in asthmatic airways and immunological markers suggest that they are activated. They play an important role in orchertraing and perpetuating the chronic asthematic response.
Late onset Asthma :
Asthma can begin at any age in non atopic individuals and because the majority of these patients are adults this type of asthma is often called late onset asthma.
