Pediatric Annals

Allergy in Infancy and Childhood

William A Howard, MD

Abstract

Allergy is defined as an adverse physiologic or biologic reaction resulting from the interaction of antigen and humoral antibody or lymphoid cells, occurring in a host sensitized by prior exposure to the antigen.

Allergy was originally thought of as "a state of altered reactivity." Current usage employs the term for the adverse or harmful reactions resulting from interaction of antigen (allergen) with circulating antibody or lymphocytes, while immunity denotes the protective mechanisms exhibited by the body in response to second exposures to such antigens as bacteria, viruses, and fungal agents. The designation of a substance as an allergen connotes an adverse or damaging response to challenge, while antigens may elicit either harmful or protective responses.

Coombs and Geli1 have offered a very useful classification of allergic reactions based on the type of tissue damage produced and the mechanism by which it is elicited (Table 1). The classification is independent of the divisions of allergy and immunology into specific areas. When a definite lesion or noxious process is demonstrable, it should be possible to fit it into one of the four types outlined in the classification. In making rounds on a pediatric medical ward, it is interesting to see how many of the patients have problems in which the pathophysiology may be designated in whole or in part by one or more of these types of responses.

Atopy has been used to denote the common allergic diseases of man, and the term implies the presence of a constitutional abnormality. Ellis2 has suggested the following characteristics of this abnormality:

1. Hereditary tendency.

2. Eosinophilia of the blood and tissue secretions.

3. Selective synthesis of IgE antibody on exposure to environmental substances.

4. An increased irritability or hyperreactivity of certain tissues of the body, notably the airways and skin, on exposure to various physical and biochemical factors.

5. Presumed dysfunction of the adrenergic receptors, leading to a disturbance in metabolism of cyclic adenosine monophosphate (cAMP).

The classic manifestations of allergy - the atopic diseases, such as asthma and hay fever - are type-I reactions, as are some forms of urticaria and angioedema, and gastrointestinal manifestations. The role of type-I allergy in atopic dermatitis is less clear, since there is some evidence for type-IV involvement also. The well-known association of atopic dermatitis with the atopic diseases and the associated high IgE levels suggest a type-I mechanism, while the decreased number of lymphoctyes, and the decreased blast transformation in response to phytohemagglutinin stimulation3 suggest a defect in cell-mediated response. In any event, the etiology of atopic dermatitis is by no means clear, and it may well be a symptom complex, with multiple trigger mechanisms.

The incidence of atopic diseases is difficult to establish because of the occasional problems in diagnosis and the lack of adequate reporting. Various estimates suggest that as many as 20 per cent of the population may be affected by some sort of IgE-mediated allergic response. The incidence of asthma has been put at 3-7 per cent of the population, but most important from the pediatrician's point of view is the fact that as much as two-thirds of all asthma begins in childhood. The familial nature of the diseases of atopy may be inferred from the observations on family histories. With a bilateral family history, up to 60 per cent of offspring may have some allergic manifestations, while with a unilateral history, the incidence drops to 35 per cent. In the absence of positive family history, the incidence is put at no more than 10 per cent. Regardless of statistics, one may state with certainty that the diseases of atopy constitute a…

Allergy is defined as an adverse physiologic or biologic reaction resulting from the interaction of antigen and humoral antibody or lymphoid cells, occurring in a host sensitized by prior exposure to the antigen.

Allergy was originally thought of as "a state of altered reactivity." Current usage employs the term for the adverse or harmful reactions resulting from interaction of antigen (allergen) with circulating antibody or lymphocytes, while immunity denotes the protective mechanisms exhibited by the body in response to second exposures to such antigens as bacteria, viruses, and fungal agents. The designation of a substance as an allergen connotes an adverse or damaging response to challenge, while antigens may elicit either harmful or protective responses.

Coombs and Geli1 have offered a very useful classification of allergic reactions based on the type of tissue damage produced and the mechanism by which it is elicited (Table 1). The classification is independent of the divisions of allergy and immunology into specific areas. When a definite lesion or noxious process is demonstrable, it should be possible to fit it into one of the four types outlined in the classification. In making rounds on a pediatric medical ward, it is interesting to see how many of the patients have problems in which the pathophysiology may be designated in whole or in part by one or more of these types of responses.

Atopy has been used to denote the common allergic diseases of man, and the term implies the presence of a constitutional abnormality. Ellis2 has suggested the following characteristics of this abnormality:

1. Hereditary tendency.

2. Eosinophilia of the blood and tissue secretions.

3. Selective synthesis of IgE antibody on exposure to environmental substances.

4. An increased irritability or hyperreactivity of certain tissues of the body, notably the airways and skin, on exposure to various physical and biochemical factors.

5. Presumed dysfunction of the adrenergic receptors, leading to a disturbance in metabolism of cyclic adenosine monophosphate (cAMP).

The classic manifestations of allergy - the atopic diseases, such as asthma and hay fever - are type-I reactions, as are some forms of urticaria and angioedema, and gastrointestinal manifestations. The role of type-I allergy in atopic dermatitis is less clear, since there is some evidence for type-IV involvement also. The well-known association of atopic dermatitis with the atopic diseases and the associated high IgE levels suggest a type-I mechanism, while the decreased number of lymphoctyes, and the decreased blast transformation in response to phytohemagglutinin stimulation3 suggest a defect in cell-mediated response. In any event, the etiology of atopic dermatitis is by no means clear, and it may well be a symptom complex, with multiple trigger mechanisms.

The incidence of atopic diseases is difficult to establish because of the occasional problems in diagnosis and the lack of adequate reporting. Various estimates suggest that as many as 20 per cent of the population may be affected by some sort of IgE-mediated allergic response. The incidence of asthma has been put at 3-7 per cent of the population, but most important from the pediatrician's point of view is the fact that as much as two-thirds of all asthma begins in childhood. The familial nature of the diseases of atopy may be inferred from the observations on family histories. With a bilateral family history, up to 60 per cent of offspring may have some allergic manifestations, while with a unilateral history, the incidence drops to 35 per cent. In the absence of positive family history, the incidence is put at no more than 10 per cent. Regardless of statistics, one may state with certainty that the diseases of atopy constitute a significant portion of the pediatrician's practice and that the acute attack of asthma remains a common pediatric medical emergency.

Table

TABLE 1THE FOUR TYPES OF ALLERGIC REACTIONS

TABLE 1

THE FOUR TYPES OF ALLERGIC REACTIONS

There is some evidence to indicate that respiratory allergies, especially asthma, are increasing in severity, whether or not there is an associated increase in frequency. Admissions to hospital of children in status asthmaticus have shown a five-to-sixfold increase in our own institution over the past 10-12 years, and some other children's hospitals have had a similar experience. These increases seem to have occurred without a concomitant increase in total medical admissions.

Table

ENVIRONMENTAL CONTROL CHECKLIST

ENVIRONMENTAL CONTROL CHECKLIST

TREATMENT

There are three main objectives in the management of allergic disease:

1. To eliminate causative factors from the immediate environment, insofar as is possible.

2. To decrease immunologic reactivity.

3. To reduce tissue irritability or hyperactivity - i.e., to increase the organ threshold above the reaction level.

Available means to secure these objectives include avoidance of the offending allergen, symptomatic therapy, and specific immunotherapy.

Avoidance of the offending allergen. This has the advantage of removing the causal factors in whole or in part, which may produce sufficient improvement to obviate the need for further treatment. Total avoidance is possible for relatively few allergens, such as foods or danders, but decreased exposures to dusts, molds, and pollens may be accomplished and will be helpful to a considerable degree. Instructions for the avoidance of common household allergens will be found in almost every text and may be modified to suit individual needs.

Regardless of other methods of treatment employed, environmental control measures are an important part of management, and should be stressed early. Handouts are helpful, but not entirely adequate, and parents should be furnished full explanations for the need for such control measures, and the methods used should be explained carefully. Parents should also have a chance to read the instructions and then ask appropriate questions to clarify any misunderstandings. It is appropriate to indicate that not only are there numerous allergens about the house but that there may also be other trigger mechanisms about the house that may adversely influence any allergic problem (see box).

Symptomatic therapy. This is the sheet anchor of management and revolves around a pharmacologic attack on the allergic mechanisms and the manifestations of allergic disease. In addition, one will seek control of infection when it is present, and will pay attention to other physical factors that may influence the allergic response. These mechanisms, when combined, will tend to lessen tissue irritability and increase organ threshold. Drug therapy is discussed in detail in subsequent pages of this issue.

Specific immunotherapy. To decrease the immunologic reactivity of the shock tissue requires an attempt at decreasing host response to the antigen. Immunotherapy should be used only when cause-and-effect relationships are reasonably certain and in situations where environmental control measures are inadequate or not feasible. Immunotherapy should not be used without every effort's being made to avoid the offending allergen. This form of treatment is applicable to such antigens as dusts, pollens and molds, and, under certain circumstances, animal danders.

The pediatrician's role in immunotherapy is suggested in Table 2. A pediatrician may elect to test and treat the allergic patient himself rather than referring him to a specialist. To do so requires only that one have the appropriate interest in and knowledge of the subject and the amount of time necessary to do the job adequately.

As the table indicates, selection of appropriate patients is important. A careful history must be taken and appropriate physical and laboratory examinations made, and whatever tests are needed to make the differential diagnosis ordered. Patients who do not respond to treatment, those with a history of hospitalization for allergic status, intractable asthmatics, and those with multiple allergies should be referred.

PROGNOSIS

The outlook for the child with significant allergies will depend on many factors, including:

1. Socioeconomic status.

2. Patient and/or parent compliance, based both on willingness and ability to carry out the responsibilities of treatment.

3. Severity of the allergic manifestations.

4. Nature of the disease - e.g., asthma, rhinitis, eczema.

5. Degree of allergic involvement, as opposed to other etiologic or triggering factors that may be present.

6. The interest of the physician and his willingness to guide and supervise total management.

Whether or not the allergist is involved in overall management, the pediatrician's knowledge of the patient and the family makes him the logical person to assume primary responsibility for the patient. With cooperation and assistance from the allergist when needed, the outlook can be excellent. Experience suggests that 80-90 per cent of these patients can be helped, and with appropriate treatment one may eventually expect 80-90 per cent relief of symptoms. No Can be "cured" of his allergies. In spite of spontaneous changes in allergic reactivity and such success as may be achieved in agement, the allergic state remains and become overt at any time.

Table

TABLE 2THE PEDIATRICIAN'S PARTICIPATION IN IMMUNOTHERAPY

TABLE 2

THE PEDIATRICIAN'S PARTICIPATION IN IMMUNOTHERAPY

BIBLIOGRAPHY

1. Coombs R. R. A., and Gell, P. G. H. classification of allergic reactions responsible for clinical hypersensitivity and disease. In Cell, P. G. H., Coombs, R. R. A., and Lachman, P. J. (eds.). Clinical Aspects of Immunology. London: Blackwell Scientific Publications, 1975.

2. Ellis, E. F. Allergic disorders. In Vaughan, V. C., and McKay, R. J. (eds.). Nelson Textbook of Pediatrics, 10th edition. Philadelphia: W. B. Saunders company, 1975, p. 493.

TABLE 1

THE FOUR TYPES OF ALLERGIC REACTIONS

ENVIRONMENTAL CONTROL CHECKLIST

TABLE 2

THE PEDIATRICIAN'S PARTICIPATION IN IMMUNOTHERAPY

10.3928/0090-4481-19790801-05

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