Clinical Allergy and Immunology: Key Diseases, Diagnosis, and Management Protocols

Posted on Nov 5, 2025 in Medicine & Health

Urticaria (Hives)

  • Related Condition: Angioedema.
  • Manifests as rashes all over the body.
  • Skin Layers Involved: Upper layers of the dermis.
  • Itching Mechanism: H1 receptor activation by histamine.
  • Main Symptoms of Hives: Local edema, erythema, and itching.
  • Duration of Exposure (Individual Lesion): Typically 24 to 48 hours.
  • Can be confused with urticarial vasculitis.
  • Chronic Spontaneous Urticaria (CSU): Diagnosed if symptoms persist for more than 6 weeks.
  • CSU Rash Characteristics: Size and shape of the rashes show no difference compared to acute urticaria.
  • Treatment Principle: Antihistamines (H1 receptor blockers).
  • Dosing Example: Increase dose up to 4 tablets in 7 days (Note: Specific dosing depends on the medication and patient response).

Atopic Dermatitis (Eczema)

  • Symptoms: Dry, itchy skin, often presenting as eczema.
  • Etiology: Genetically determined (familial predisposition).
  • Pathophysiology: Dry skin indicates increased intradermal water loss.
  • Onset: Clinically manifested often in infancy.
  • Presentation: Different age groups usually exhibit different predilection zones (locations of rashes).
  • Prevention: Regular use of emollients.
  • Treatment: Topical corticosteroids and oral antihistamines.
  • Environmental Management: Avoid prolonged stays in dry environments.

Bronchial Asthma

  • Affected Organ: Bronchi.
  • Pathology: Desquamation of bronchial epithelium.
  • Inflammation Marker: Eosinophils are present during chronic inflammation.
  • Triggers: Bronchospasm provoked by nonspecific irritants (e.g., cold air, strong odors).
  • Primary Treatment: Inhaled corticosteroids (affect the allergic inflammation).
  • Optimal Candidate for Allergen-Specific Immunotherapy (ASIT): A young patient with monoallergy to pollen achieves the best effect.

Anaphylactic Shock

  • Mechanism: IgE-mediated (Type I Hypersensitivity).
  • Pathogenesis: Primarily due to mast cell degranulation.
  • Progression: Typically occurs in two phases (early and late).
  • Early Phase Duration: 5 to 30 minutes.
  • Mediators:
    • Initial changes are due to histamine release.
    • Prostaglandins and leukotrienes are prominent in the late stage.
  • Defining Feature: Inability to control hypotension.
  • Systems Involved: Cardiovascular, respiratory, gastrointestinal, and skin.
  • Potential Cause: Reaction to heterologous serums.
  • Contraindication: Do not use beta blockers.
  • Emergency Management Protocol:
    1. Removal of the allergen.
    2. Trendelenburg position.
    3. Subcutaneous adrenaline (epinephrine).
    4. Infusion of saline aqueous solutions.

Drug Allergy

  • Often related to food allergy mechanisms.
  • Can occur via any of the hypersensitivity mechanisms (Type I, II, III, or IV).
  • Severe Manifestation Example: Lyell’s syndrome (Toxic Epidermal Necrolysis).
  • Common Triggers: Antibiotics of the penicillin group.
  • Testing Methods: Scarification test and provocative tests are the main approaches.
  • Pre-Surgical Management: Patients requiring surgery who are sensitive to anesthetics and muscle relaxants should be tested and pre-treated with antihistamines and corticosteroids.

Allergen-Specific Immunotherapy (ASIT)

  • Mechanism: Induces the production of IgG4 antibodies (blocking antibodies).
  • Indication: Highly successful for insect allergy (most successful).
  • Contraindication: Not used for treating Atopic Dermatitis or Food Allergy.
  • Administration: Not used intravenously.
  • Timing: Treatment for allergic rhinitis or bee/wasp sting allergy is typically started outside the pollen season.
  • Observation Period: Patients are usually observed for 30 minutes post-injection.
  • Pre-Treatment Requirement: Stop taking beta blockers before starting ASIT.
  • Most Severe Adverse Effect: Anaphylactic shock.

Food Allergy

  • Diagnosis Protocol: Often involves a 4-step protocol.
  • Pathogenesis: Related to impaired oral tolerance.
  • Mechanism: May occur by any hypersensitivity mechanism.
  • Provocative Food Test Requirement: The patient must be asymptomatic prior to testing.

Hereditary Angioedema (HAE)

  • Nature: An independent illness (not allergic).
  • Etiology: Due to C1 esterase inhibitor deficiency.
  • Affects both sexes.
  • Clinical Presentation: Can mimic an acute surgical abdomen.
  • Treatment/Prophylaxis:
    • Treatment involves infusion of fresh isogroup plasma.
    • Prophylaxis: Infuse fresh isogroup plasma 2 hours before surgery.

Allergic Rhinitis (Hay Fever)

  • Comorbidities: Related to Atopic Bronchial Asthma and Atopic Dermatitis (Atopic March).
  • Nasal Mucosa Appearance: Pale, livid, and edematous.
  • Classification: Intermittent and persistent types.
  • Association: Pollen allergic rhinitis is often associated with Oral Allergic Syndrome.
  • Diagnosis:
    • Skin tests with allergens.
    • Nasal wash analysis shows eosinophils.
    • Rhinomanometry is a test used for each type of rhinitis.
    • Wilcox test (used for classification/diagnosis of all types of rhinitis).
  • Treatment Warning: Nasal decongestants should be used only during periods of exacerbation for no more than 3–5 days to prevent rebound congestion.

Allergy Skin Testing Protocols

Immediate Hypersensitivity Tests (Type I)

Requires stopping antihistamines 5–7 days before performing the scarification, prick, or intradermal test.

  • Prick Test: Positive result is typically defined as a wheal diameter above 3 mm. Results reported in 20 minutes.
  • Scarification Test: Positive result is typically defined as a wheal diameter above 3 mm. Results reported in 20 minutes.
  • Intradermal Test: Positive result is typically defined as a wheal diameter above 7 mm. Results reported in 20 minutes.

Delayed Hypersensitivity Test (Type IV)

  • Patch Test:
    • Mechanism: Type IV Hypersensitivity.
    • Timing: Results reported after 72 hours.
    • Pre-Test Requirement: Stop corticosteroids before performing the patch test.

Bronchodilator Reversibility Test

  • Positive Result: FEV1 improvement above 15%.
  • Indication: Used in patients with reduced spirometry and changes in physical lung status.
  • Pre-Test Requirement: The patient must stop treatment with Long-Acting Beta-2 Agonists (LABAs) 12 hours before the test.

Non-Specific Bronchial Challenge Test

  • Positive Result: Reduction of the initial FEV1 by 20% when challenged with methacholine.
  • Indication: Used in asymptomatic patients who have normal spirometry but a history suggestive of asthma (e.g., chronic cough and shortness of breath).

Insect Sting Allergy

  • Most Severe Reactions: Caused by Hymenoptera (bees and wasps).
  • ASIT Timing: Allergen-Specific Immunotherapy (ASIT) to bee or wasp venom is typically started at the end of the autumn season.
  • ASIT Indication Post-Anaphylaxis: The proper medical behavior for patients who have experienced anaphylactic shock after bee or wasp stings is to conduct ASIT.
  • ASIT Contraindication: ASIT should not be conducted in case of unusual late allergic reactions after a bee or wasp sting.
  • Other Allergens: Cockroaches are insects known to cause atopic bronchial asthma.
  • Mechanism (Blood-Sucking Insects): Blood-sucking insects most often cause allergies via immune complex mechanisms (Type III Hypersensitivity).
  • Non-Bee Venom Reaction: Fredericks Syndrome is not a reaction due to bee venom.

Angioedema

  • Appearance: Pale edema, often accompanied by itching (when allergic).
  • Location: Affects the skin and mucous membranes all over the body.
  • Emergency Treatment: For angioedema of the upper respiratory tract accompanied by inspiratory dyspnea, the first drug of treatment is Adrenaline (Epinephrine).