notes by dr Claudio Italiano
The food allergy is a condition when a substance with antigenic determinants, parts of it that stimulate the body's immune system, comes into contact with special cells of the white series, called plasma cells, which have receptors for a particular class of immunoglobulins, the IgE. The atopic organism, in front of an allergic substance, produces this type of antibodies and when the allergen comes into contact with the antibody, which in turn is conveyed with the plasma cells, the "allergic reaction" is determined.
Even in the case of allergens introduced with food it is possible to have a reaction mediated by the reagin or IgE, especially if we are faced with individuals who have been breastfed with infant formula and not maternal, in the early stages of their lives, when it was necessary that the digestive tract matured and learned to recognize allergens from good substances. 1-2% of the population are affected, with a prevalence of females F: M = 2: 1; and a frequency peak in childhood, moreover 2/3 of you suffer from other atopic diseases (allergic rhinitis, bronchial asthma, atopic dermatitis.
Generally they are substances introduced into food by human manipulation, such as additives and dyes, or allergens naturally contained in some foods (strawberries, crustaceans, molluscs, etc.).
Frequent allergens are those of cow's milk (common allergen in children), chicken eggs, crustaceans, soybeans, nuts, cereals. In a certain sense, even celiac disease, as an intolerance to gluten gliadins, could be framed in these clinical pictures; then come celery, some fruit, spices, yeasts, molds. The majority of patients allergic to fresh fruit are also affected by cross-pollen allergy (see respiratory allergy) (eg birch pollen with apples / hazelnuts, wormwood pollen with celery / carrots and spices). Even in the case of a latex allergy, cross-reactions with food can occur, e.g. avocados, bananas, figs, etc.).
The following allergic reactions have been observed:
-
types I / immediate reaction, already after 0-1 hour IgE mediated with release
of histamine from mast cells.
- type III / intermediate reaction, after 1-20 hours, mediated by IgG
-
type IV / delayed reaction (after 20 h) = cell-medium reaction
The organic manifestations of food allergies are as follows:
1) skin: urticaria, Quincke's edema, pruritus, exanthema in 50% of cases;
Urticaria / acute angioedema. Characterized by itching, burning and swelling
that vary considerably by extension and duration. Angiooedema (skin swelling)
does not cause itching but tingling, warmth and a feeling of tension on an
edematous skin. They are among the most common symptoms of food-induced allergic
reactions. Food allergy is rarely the cause of urticaria and chronic angioedema
(symptoms that last for more than 6 weeks).
2) airways: laryngeal edema, asthma, rhinitis in 20% of cases;
Rhinoconjunctivitis. It is rarely the result of an allergic food-induced
reaction although it often manifests itself in association with other food
allergy symptoms.
Asthma. It is an uncommon manifestation of food allergy, although acute bronchospasm is usually observed with other food-induced symptoms. However, respiratory hyperreactivity and worsening of asthma can also be induced in the absence of marked bronchospasm after ingestion of small quantities of food allergens in sensitized individuals. It is interesting to note that food allergy has recently been identified as one of the major risk factors for potentially fatal asthma. Vapors and exhalations containing proteins emitted by food during cooking (eg fish) can induce asthmatic reactions and even anaphylaxis has been calculated that about 1% of asthma in adults could involve reactions to inhaled exposure to food, especially in the workplace .
3) gastrointestinal tract: "oral allergic syndrome", itching and dermatological
alterations to lips and palate (especially in case of cross-allergy with artemisia pollen); rarely vomiting, abdominal cramps, diarrhea in 20% of cases.
Allergic oral syndrome or pollen-food syndrome. It is characterized by itching
and burning of the oral mucosa and edema of the lips immediately after the
ingestion of plant foods. It is present in many pollinosic subjects and is
caused by the presence of proteins (allergens) common between pollens (eg birch,
ambrosia and artemisia) and plant foods (eg banana, melon, potato, carrot,
celery, apple, pear , hazelnut and kiwi). Because the allergens responsible for
these reactions are easily destroyed by heat or gastric enzymes, most patients
have symptoms limited to oral and pharyngeal mucosa. Gastrointestinal
anaphylaxis. It typically presents with rapid onset of nausea, colonic abdominal
pain, vomiting and diarrhea; generally occurs in conjunction with other allergic
manifestations in other target organs such as the skin and the respiratory tract.
4) systemic manifestations: tachycardia, blood pressure drop, anaphylactic shock
in 10%, fortunately less frequently.
Anaphylaxis. The generalized anaphylaxis caused by food allergies is responsible
for at least one third by at least half the cases of anaphylaxis seen in the
hospital emergency units. In addition to the different expressions of skin,
respiratory and gastrointestinal symptoms, patients may have cardiovascular
symptoms including hypotension, vascular collapse and arrhythmias. Curiously,
serum beta-tryptase levels are rarely increased in food-induced anaphylaxis. In
an observational study of food induced anaphylaxis, a number of risk factors
emerged for food-induced anaphylaxis:
There are pseudo-allergic reactions that have the same symptoms with respect to
allergy, as both reactions are triggered by the release of histamine from tissue
mast cells. The degranulation of mast cells in case of allergy is triggered, as
said, by the binding of the allergen to the IgE present on the mast cell
membrane. In the pseudo-allergic reaction, degranulation, on the other hand, is
induced directly (= irrespective of any antibodies) with a pharmacological
mechanism:
- pseudo-allergic reactions from non-specific histamine liberators present in
foods (eg strawberries, tomatoes)
- pseudo-allergic reactions from vasoactive substances present in food, e.g.
histamine sauerkraut cheese, wine, canned fish), serotonin (bananas, walnuts),
tyramine (cheese, chocolate, red wine) (see also headache crisis). Some drugs
inhibit the intestinal diamino-oxidase enzyme. In this case the histamine
catabolism is inhibited, which is thus absorbed in greater quantities by food.
This can trigger, in predisposed patients, heart and circulatory disorders due
to histamine.
Diagnosis: based on dietary and pharmacological history + demonstration of the
increase in plasma levels of histamine at the time of symptoms.
- pseudo-allergic reactions from food additives: e.g. tartrazine (E102), benzoic
acid (E124-219), sulphite (E220-227), bisulfate (in white wine)
- pseudo-allergic reactions from naturally occurring salicylates, e.g. in the
fruit
- pseudo-allergic reactions from sodium glutamate (Chinese restaurant syndrome)
Following the consumption of foods containing monosodium glutamate (soy sauce!),
The following typical symptoms may occur in case of individual predisposition:
feeling of weakness, sweating, palpitation, headache, etc.
2. Lactase deficiency
Note: there are two causes of cow's milk intolerance: lactase deficiency (frequent)
and milk protein allergy (casein in 70% of cases, less frequently lactobumin,
rarely beta-lactoglobulin). While the patient with lactase deficiency can still
withstand small amounts of milk, the allergic person reacts to the slightest
amount of milk and experiences disturbances.
History:
identification of suspicious foods that cause gastrointestinal disorders
protocol for the patient).
Exclusion of other gastrointestinal diseases.
Elimination and provocation diet:
the patient must follow a low allergen-based diet for 7 days (eg diet based on
rice, potatoes, water). If the symptoms persist, then it is unlikely that the
food allergy is the cause (except in cases of allergy to rice or potatoes, which
can be excluded by RAST or skin tests.If the symptoms disappear, then add man
hand single foods until the disturbances appear again Criteria for a positive
provocation test:
-
new manifestation of gastrointestinal or extraintestinal disorders
- laboratory parameters:
-
decrease in thrombocytes and / or leukocytes
- increase in plasma histamine.
4. Skin tests + RAST (demonstration of specific IgE antibodies) to identify
possible allergens Only the positivity test proves the clinical significance of
an allergen identified by RAST or skin test. In atopic subjects RAST often
documents a sensitization to various food allergens, even if the corresponding
foods are taken without the appearance of symptoms.
5. Evtl. Colonscope allergic provocation test: exposure of intestinal mucosa to
suspected allergens under colonscopic control.
The most important measure is the elimination from the allergen diet!
In the case of ubiquitous basic foods, such as milk and eggs, elimination is
difficult.
General dietary advice:
when identification and elimination of the allergen diet are not possible, it is
recommended to try to eliminate the following foods / beverages
• raw food or freshly heated food (adequate heating inactivates some allergens)
• fruit salad and exotic fruits
• alcoholic drinks, fruit juices
• cold and abundant meals.
In case of anaphylactic reaction from food, provide adequate dietary
instructions to the patient and prescribe the drugs to be kept ready for any
emergency treatment (adrenaline a phial diluted in physiological by aerosols,
water-soluble corticosteroids, antihistamines); do not prescribe beta-blockers
(reduce the effect of any adrenaline therapy). Hyposensitizing therapy can be
useful in case of allergy to cow's milk cross-allergic with pollen; it is
however of specialized competence.
Attempt to pharmacological prophylaxis:
- antihistamines
- mast cell stabilizers, e.g. disodiocromoglycate, ketotifen.
Useful for the newborn with a positive family history of atopic conditions: do
not keep pets and give up smoking; in the first 6 months of life only milk but-
and simultaneous elimination diet in the mother (no cow's milk, peanut eggs);
for the child, it may also be supplied with hydrolysates that are poor in
allergens. By avoiding exposure to responsible allergens for many years, the
allergy can also disappear (in children in 50% of cases, in adults in 30%).
index topic on gastroenterology