Extrinsic Versus Intrinsic Asthma
Asthma is often divided into either an allergic or “extrinsic” type that commonly has its onset in childhood, and an adult onset or “intrinsic”type. Although there is considerable overlap between these groups, it is helpful to classify patients according to several features that distinguish them.
Extrinsic Asthma
Extrinsic patients are younger and have attacks clearly triggered by exposure to allergens such as pollens, dust, animal dander, foods, and molds. These patients often have strong family histories of relatives with allergies or asthma. Allergy treatment known as desensitization has often been helpful in these patients. For many years it has been thought that the majority of these patients “outgrew” their asthma by age thirty, but recent evidence suggests that 75 percent remain asthmatic for life. These patients may have long symptom free periods.
Intrinsic Asthma
Intrinsic group patients often develop asthma as adults, and at any age. Often the trigger for these attacks is infection with involvement of the lower respiratory tract as in bronchitis or pneumonia. Some of the most severe infections of this type are viral but they may also be bacterial. Patients in the intrinsic group usually do not have histories of allergies and produce negative allergy tests. Once the diagnosis is evident, further attacks are often triggered by less severe infections. There are fewer symptom free periods in this group and these patients usually require medication for life.
Should This Classification Be Used
Many practitioners no longer use this older classification of the types of bronchial asthma. When discussing the future outlook of the disease as well as treatment options, I find it helpful to use these two general classes of asthma to provide simple guidelines that can be followed. In the younger, highly allergic, or extrinsic asthmatic, for example, emphasis on avoidance of allergens will be extremely important.
