ملخص

Allergy is a medical term which means that the patient develops symptoms upon contact with allergens to which he/she is sensitized

Atopy is inappropriate (exaggerated) IgE antibody production to harmless environmental substances (allergens) in a genetically predisposed individual but not necessarily develops symptoms (silent).
So, atopy is a condition for the development of allergy but is not itself allergy (i.e. you need to be atopic to become allergic, but not all atopic people develop allergy).

Pseudo-allergy/anaphylactoid

Cause similar symptoms to allergy They are caused by the release of histamine and results in a spectrum of symptoms vary from rash to anaphylaxis. They are usually caused by aspirin, NSAIDs

allergic reaction occurs within minutes after exposure to allergens

Management urticaria
1. Non-sedative antihistamine
2. If no response, add H2-blocker
3. Mast cell stabilizers or leukotriene inhibitors (montelukast ).
4. Systemic corticosteroids are widely used.

Urticaria

Is an area of focal dermal oedema secondary to transient increase in capillary permeability. When present for <6 weeks it is an acute urticaria (may be associate with angioedema of lips, face or throat), and for >6 weeks it s a chronic urticaria. Urticaria is characterized by itching.


Types of angioedema
1. Allergic reaction to specific triggers; treated with anti-histamine
2. Idiopathic angioedema; treated with anti-histamine
3. Hereditary angioedema; treated with modified androgen derivative (danazol),
4. ACE-inhibitor (ACEI) associated angioedema ; stop the medication

Angioedema

localized, non-pitting swelling of submucous or subcutaneous tissues. characterized by pain without itching.

Anaphylaxis

It is a potentially life- threatening, systemic allergic reaction caused by degranulation of mast cells and release of vasoactive amines. Death may occur if the patient has a preexisting asthma or adrenaline (epinephrine) administration is delayed.

Anaphylaxis starts in few minutes up to one hour

Management of Anaphylaxis
Anaphylaxis is an acute medical emergency, and should be handled immediately:
1. Prevent further contact with allergen
2. Ensure airway
3. Administration of I.M. adrenaline immediately
4. Administration of antihistamine
5. Administration of corticosteroids
6. Supportive treatments including:
A. Nebulised beta2-agonist to decrease brochocontriction
B. I.V. fluid to restore or maintain B.P.
C. Oxygen
D. Keep the patient in an Intensive Care Unit (ICU) for 12 hours.


General investigations for allergic diseases

Skin prick test

Specific IgE tests
Total serum IgE and eosinophilia
Raised or normal IgE level may present in allergy. Eosinophilia is common in atopic individuals, but >20% may be due to non-atopic causes.
Challenge test
Mast cell tryptase
The peak of serum level is after 1-2 hours of exposure .

General management of allergy

1. Avoidance in the main step in the management.
2. Antihistamine (block H1 receptors) in particular the long acting, non-sedating
3. Corticosteroids decrease pro-inflammatory cytokines.
4. Sodium cromoglicate used only for prophylaxis against asthma .
5. Antigen-specific immunotherapy (hypo-sensitization/ de-sensitization)
6. Omalizumab (Xolair) is humanized monoclonal antibody (IgG1) that inhibits the binding of IgE to mast cells and basophils.