ARTICLE
Auteur(s) : J Ring, T Reunala, B Wüthrich
Definition
The term “allergy” denotes a spectrum of diseases caused by
specific immunological hypersensitivity. Allergic diseases arise
via a host of mechanisms and are clinically complex, involving many
different organs. Most commonly, they affect the skin and the
mucous surfaces, the frontiers where patients come into direct
contact with their environment.
Allergic diseases
Allergic diseases involving the skin include:
- – Urticaria (hives) and angioedema which may herald
life-threatening anaphylactic reactions;
- – Allergic contact dermatitis, one of the common
occupational diseases;
- – Drug reactions;
- – Photo-allergic diseases where both light and a
allergic reaction are required;
- – Intolerance reactions such as severe drug reactions
(Stevens-Johnson syndrome and toxic epidermal necrolysis) and some
forms of vasculitis;
- – Atopic diseases – atopic eczema with associated
allergic rhinitis (hay fever), allergic conjunctivitis, and
allergic bronchial asthma.
Etiology
Atopy occurs in families on the basis of a genetic background
associated with increased production of a certain type of
antibodies (immunoglobulin E = IgE) and altered reactivity of skin
and mucous membranes. The different manifestations may occur
together in the same individual at the same time or in alternating
cycles over time, as well as appearing in different family members.
Atopic eczema in young children and infants often precedes
bronchial asthma and hay fever.
Allergic diseases are elicited by allergens-environmental
substances, such as proteins for IgE reactions or small chemicals
for contact dermatitis. The most important allergens include
airborne substances such as pollen, moulds, house dust mite and
animal dander, as well as foods, insect venoms and drugs. Common
causes of allergic contact dermatitis are cosmetics, drugs,
occupational substances and metals.
Management
The interdisciplinary character of many allergic diseases mandates
that various disciplines be involved in the care of allergic
patients – most commonly dermatology, internal medicine/pneumology,
otolaryngology, and pediatrics. Since the majority of allergic
patients have skin involvement, the dermatologist is on the
forefront of diagnosis, prevention and treatment of many allergic
diseases.
Proper diagnosis of an allergic disease requires a four-step
procedure:
- – History and clinical examination;
- – Skin tests;
- – In vitro allergy diagnosis;
- – Provocation tests.
History and clinical examination: History-taking is the
most important step in allergy diagnosis and requires an
understanding of both the pathophysiology of allergic diseases, as
well as of the likely allergens in the patient’s environment. It
can not be replaced by automated screening tests or
questionnaires.
Diagnosis of a clinical entity on the basis of typical symptoms
and signs is a prerequisite for further diagnostic steps. For
example, a dermatologist can usually distinguish at a glance
between atopic eczema where allergy testing is essential, and
psoriasis where it is of no benefit and wastes limited health care
resources.
Skin tests: These are the most reliable technique to
document the individual sensitization against allergens by
demonstrating a specific inflammatory response to allergen in the
skin. Several different types of skin test procedures are available
for various indications. For immediate-type reactions, the friction
test, skin prick test, scratch test and intradermal test are
employed (in increasing order of potential risk). Depending upon
the history, the performance of a skin test may be associated with
a certain risk of anaphylactic reactions. For contact dermatitis,
epidermal tests (patch tests) are performed. Special techniques are
required to study photosensitization phenomena (photopatch tests,
photo-provocation test). The performance of skin tests requires
dermatological expertise to distinguish positive reactions from
false-positive and false-negative reactions.
In vitro allergy diagnosis: In vitro diagnosis of
allergic diseases includes both serological and cellular
techniques. The most important test is the detection of specific
IgE antibodies in the serum with the Radio-Allergo-Sorbent test
(RAST) or modifications of enzyme immuno assays (EIA). While
specific antibodies of other immunoglobulin classes can be detected
with similar approaches, their relevance is unclear. Antibodies
against specific components of allergen extracts can be detected by
immunoblot analysis.
The intensity of an allergic inflammation can be monitored by
measuring products released by mediator cells such as tryptase and
histamine from mast cells or basophils, eosinophil cationic protein
(ECP) from eosinophils or cytokines from activated lymphocytes. In
addition, blood cells can be incubated with allergens to assess
their response.
Provocation tests: If history and allergy tests fail to
clearly delineate the suspected allergen, provocation tests may be
performed. These include topical, mucosal and systemic tests (e.g.
oral provocation tests for food-induced urticaria,
angioedema/anaphylaxis or atopic eczema). Provocation tests should
be performed under placebo-controlled (ideally double-blind)
conditions.
In a sub-group of patients with atopic eczema, the atopy patch
test using IgE-inducing allergens in a classical patch test
procedure has proven valuable.
The correct interpretation of test results can only be
accomplished by experienced specialists who can integrate the
laboratory results with patients’ history, skin and – if applicable
– provocation tests. To make a diagnosis of an allergic disorder
only on the basis of in vitro test results is not good clinical
practice.
Therapeutic strategies
The ideal management of allergic diseases is avoidance of
allergens, once they have been correctly identified, emphasizing
again the need for precise allergy diagnosis. Avoidance cannot be
achieved because of the ubiquitous nature of many allergens.
Other strategies include the elimination of non-specific
irritants, recommendation of specific diets in food allergy,
consultation for change in occupation or daily work, removal or
reduction of indoor air allergens (e.g. house dust mites) and
rehabilitation approaches in low-allergen environments (at sea
level or at high altitude over 1500 m).
The only curative strategy – besides allergy avoidance – is the
correction of the deviated immune response by allergen-specific
immunotherapy (= specific hyposensitization). This therapeutic
approach has been successfully used for decades for respiratory
allergies and insect venom anaphylaxis/urticaria. Specific
immunotherapy for food allergy and atopic eczema is under current
investigation.
Pharmacotherapy of immediate-type IgE-mediated allergic diseases
includes the prophylactic use of mast cell stabilizers
(cromoglycates) as well as specific receptor antagonists of
vasoactive mediators (e.g. antihistamines or antileukotrienes).
Emergency treatment of anaphylaxis comprises a hierarchy of 4
essential procedures: intravenous fluid application, i.v.
antihistamines, i.v. high-dose glucocorticosteroids, epinephrine
and – if applicable – cardio-pulmonary resuscitation.
Antiinflammatory treatment is the mainstay of therapy for both
allergic contact dermatitis and atopic eczema. It includes the use
of topical glucocorticosteroids or the newly-developed topical
calcineurin antagonists. Restitution of the disturbed skin barrier
function with emollients and avoidance of irritating substances is
also essential. Phototherapy or photochemotherapy (PUVA) may serve
as adjuvant modalities in chronic cases. Rarely, systemic
immunosuppression, including systemic glucocorticosteroids, may be
required in very severe cases.
Psychosomatic interactions not infrequently play a role as
trigger factors in exacerbating or maintaining allergic skin
diseases (atopic eczema, chronic urticaria and others).
Psychosomatic counseling or psychopharmacotherapy have a place in
the management of these patients. In allergic skin diseases –
probably more than in other medical conditions – there is an
increasing trend towards “complementary” medicine (also
“unconventional” or “alternative” procedures). Most of these
“miracle” treatment options are not scientifically reproducible and
cannot be recommended as serious options.
Newer options include the use of “biologicals”, such as
recombinant cytokines or monoclonal antibodies to stimulate or
suppress key steps in the allergic reaction (e.g. anti-IgE,
anti-interleukin-5, interleukin 10 and others). The exact
therapeutic role of these agents is being defined in experimental
studies and clinical trials.
Prevention strategies
The dermatologist plays an important role as “manager” or counselor
of allergic patients and their parents with regard to many aspects
of daily life. Prevention strategies are of particular importance
in allergic diseases. Early diagnosis and then allergen avoidance
are the basis of secondary and tertiary prevention. This requires
appropriate diagnosis and counseling regarding environmental
allergen sources (home, occupational setting, cosmetics, clothes).
Skin care using individually-adapted emollients as well as
appropriate hygienic measures are crucial. Two key aspects of
prevention are informing the patient about the occurrence of
allergens in his environment and insuring better content
declaration regulations (not only for drugs and cosmetics, but also
for daily life items) to make allergen avoidance easier.
Educational programs (“eczema schools”) teach the patient coping
strategies with regard to the itch-scratch cycle, stress avoidance,
and relaxation techniques. In severe cases, inpatient
rehabilitation – sometimes under climatotherapy conditions – is
indicated.
Outlook
Unfortunately, in Europe many allergic patients are still
improperly diagnosed and not adequately treated since they are not
seen by specialists. Although allergic diseases have increased in
prevalence over the last decades, they are not properly represented
in the curriculum of medical students in many European
universities. This has to be changed. Experimental and clinical
allergology has to be included in teaching programs for medical
students with obligatory examinations. In training programs for
residents in dermatology, management of allergic diseases must be
an integral part of the training. Certification for residency
training in dermatology should include criteria regarding the
performance of allergy diagnosis and treatment.
The interdisciplinary character of allergology implies a close
cooperation between relevant disciplines in the management of
allergic patients. Increasing efforts are required in basic
research, education and patient care in order to assure better care
for the large and rapidly increasing number of patients with
allergic disease in Europe.
|
Printable version
Version PDF